Updated on 2021/11/13

写真a

 
MIZUGUCHI Masaki
 
Organization
Institute of Materials and Systems for Sustainability Division of Materials Research (DM) Professor
Graduate School
Graduate School of Engineering
Graduate School of Engineering
Title
Professor
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Degree 2

  1. 博士(工学) ( 2003.3   東京大学 ) 

  2. 修士(工学) ( 2000.3   東京大学 ) 

Research Interests 8

  1. 薄膜

  2. 磁性材料

  3. 磁性

  4. 熱電変換

  5. 熱磁気効果

  6. スピントロニクス

  7. スピンカロリトロニクス

  8. エネルギー材料

Research Areas 10

  1. Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Electric and electronic materials

  2. Nanotechnology/Materials / Metallic material properties

  3. Energy Engineering / Quantum beam science

  4. Nanotechnology/Materials / Thin film/surface and interfacial physical properties

  5. Nanotechnology/Materials / Crystal engineering

  6. Natural Science / Magnetism, superconductivity and strongly correlated systems

  7. Nanotechnology/Materials / Inorganic compounds and inorganic materials chemistry

  8. Nanotechnology/Materials / Applied physical properties

  9. Nanotechnology/Materials / Fundamental physical chemistry

  10. Nanotechnology/Materials / Nanomaterials

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Current Research Project and SDGs 1

  1. 熱磁気効果を利用した環境発電技術の開発

Research History 5

  1. Nagoya University Graduate School of Engineering Materials Process Engineering   Professor

    2020.5

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  2. Tohoku University   Institute for Materials Research   Associate professor

    2009.5 - 2020.4

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  3. 量子科学技術研究開発機構   先端機能材料研究部   客員研究員 (兼任)

    2020.5

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  4. 東京大学 大学院   工学系研究科   非常勤講師 (兼任)

    2015.10 - 2016.3

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  5. Kagoshima University

    2014.11 - 2015.3

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Education 1

  1. 東京大学 大学院   工学系研究科   応用化学専攻 博士課程

    2000.4 - 2003.3

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Professional Memberships 8

  1. Institute of Electrical and Electronics Engineers

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  2. THE JAPAN INSTITUTE OF METALS AND MATERIALS

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  3. The Japan Society of Vacuum and Surface Science

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  4. THE MAGNETICS SOCIETY OF JAPAN

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  5. THE PHYSICAL SOCIETY OF JAPAN

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  6. THE JAPANESE SOCIETY FOR SYNCHROTRON RADIATION RESEARCH

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  7. THE CHEMICAL SOCIETY OF JAPAN

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  8. THE JAPAN SOCIETY OF APPLIED PHYSICS

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Committee Memberships 10

  1.   IEEE MAG-33 Nagoya Secretary & Treasurer  

    2021.1   

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  2. SPRUC ナノスピントロニクス研究会   代表  

    2020.4   

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  3. 文部科学省 科学技術・学術政策研究所科学技術予測センター   専門調査員  

    2019.6   

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    Committee type:Government

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  4. 国際会議: ISSS-9 (9th International Symposium on Surface Science)   Program Committee  

    2019.1   

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    Committee type:Academic society

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  5. 次世代放射光施設利用検討委員会   分科会委員  

    2019.1   

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    Committee type:Other

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  6. SPring-8ユーザー協同体   利用委員会委員 (分野融合担当 (ナノデバイス科学))  

    2017.8 - 2019.9   

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    Committee type:Academic society

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  7. 国際論文誌: Science and Technology of Advanced Materials (STAM)   編集委員  

    2017.4   

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    Committee type:Academic society

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  8. 日本物理学会   領域3 運営委員  

    2017.4 - 2018.3   

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    Committee type:Academic society

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  9. 応用物理学会 スピントロニクス研究会   幹事  

    2013.9   

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    Committee type:Academic society

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  10. 日本磁気学会   スピントロニクス専門研究会 世話人  

    2011.4   

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Awards 5

  1. 永井科学技術財団賞 学術賞

    2021.3   公益財団法人永井科学技術財団  

    水口将輝

  2. 永井科学技術財団賞 学術賞

    2021.3   永井科学技術財団  

    水口将輝

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  3. 第5回テクノバ賞

    2020.12   株式会社 テクノバ  

    水口 将輝

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  4. 2019年度 矢崎学術賞(功績賞)

    2020.3   公益財団法人 矢崎科学技術振興記念財団  

    水口 将輝

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  5. 2019年度(第9回)RIEC Award 東北大学研究者賞

    2019.11   一般財団法人 電気通信工学振興会  

    MIZUGUCHI Masaki

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Papers 179

  1. Nanostructure design for high performance thermoelectric materials based on anomalous Nernst effect using metal/semiconductor multilayer

    Reona Kitaura, Takafumi Ishibe, Himanshu Sharma, Masaki Mizuguchi, Yoshiaki Nakamura

    Applied Physics Express   Vol. 14 ( 7 ) page: 075002 - 075002   2021.7

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    Publishing type:Research paper (scientific journal)   Publisher:IOP Publishing  

    DOI: 10.35848/1882-0786/ac05db

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    Other Link: https://iopscience.iop.org/article/10.35848/1882-0786/ac05db/pdf

  2. MgO template effect for perpendicular magnetic anisotropy in (001)-textured poly-crystalline MnAlGe films Reviewed

    Takahide Kubota, Keita Ito, Rie Y. Umetsu, Masaki Mizuguchi, Koki Takanashi

    AIP Advances   Vol. 11 ( 1 ) page: 015124 - 015124   2021.1

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    Magnetic thin films showing high perpendicular magnetic anisotropy, K-u, and low saturation magnetization, M-s, are essential for realizing a small switching current in spintronic devices utilizing the current induced magnetization switching phenomena. The Cu2Sb-type MnAlGe intermetallic compound is a material showing uniaxial magnetocrystalline anisotropy with a relatively low M-s, which is attractive for spintronic application. In this study, the layer thickness dependence of K-u was investigated in poly-crystalline MnAlGe films, and the MgO template effect is discussed to achieve perpendicularly magnetized films in a few-nanometer thickness range. Experimental results suggested that the (001)-texture for the perpendicular magnetization was promoted by the MgO(001) template through the solid-phase epitaxy growth by annealing, which is similar with that in conventionally used CoFeB|MgO layered samples. K-u of about 2 x 10(6) erg/cm(3) was achieved in a 5 nm-thick MnAlGe film using MgO buffer and capping exhibiting a low M-s value of approximately 200 emu/cm(3) at room temperature. Although the magnitude of K-u is still in a moderate range, the low M-s is a promising feature for spintronic application.

    DOI: 10.1063/9.0000138

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  3. Synthesis of Ferromagnetic τ-Mn–Al–C by Reactive Sintering Reviewed

    Ryota Kobayashi, Yoshifuru Mitsui, Rie Y. Umetsu, Masaki Mizuguchi, Keiichi Koyama

    MATERIALS TRANSACTIONS   Vol. 62 ( 1 ) page: 130 - 134   2021.1

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    Publishing type:Research paper (scientific journal)   Publisher:Japan Institute of Metals  

    DOI: 10.2320/matertrans.mt-m2020166

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  4. Dual Acceleration of ε-τ Transformation in Mn–Al Induced by Zn-Addition and In-Magnetic-Field Annealing Reviewed

    Ryota Kobayashi, Akio Takaki, Yoshifuru Mitsui, Rie Y. Umetsu, Kohki Takahashi, Masaki Mizuguchi, Keiichi Koyama

    MATERIALS TRANSACTIONS   Vol. 62 ( 1 ) page: 124 - 129   2021.1

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Japan Institute of Metals  

    Combined accelerating effects of epsilon-tau phase transformation by in-magnetic-field annealing and Zn-addition were investigated for Mn53Zn2Al45 in magnetic fields up to 15 T. The in-field annealing for Zn-added sample accelerated the epsilon-tau transformation 16 times faster than Mn53Zn2Al45 at annealing temperature of 623 K. The reduction of magnetization after finishing epsilon-tau transformation was also more rapid than that of Mn53Zn2Al45. However, magnetic-field-induced acceleration of epsilon-tau phase transformation and suppression of precipitation of beta-phase were observed for Zn-added alloy Mn53Zn2Al45 annealed at 573 K. The obtained results suggested that the beta-phase stabilized against both alpha- and epsilon-phases by Zn-addition. Therefore, although the epsilon-tau transformation was efficiently accelerated by in-field annealing of Mn53Zn2Al45, more precisely control of annealing time is required for obtaining high fraction of ferromagnetic tau-phase.

    DOI: 10.2320/matertrans.mt-m2020235

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  5. Scanning magneto-optical Kerr effect (MOKE) measurement with element-selectivity by using a soft x-ray free-electron laser and an ellipsoidal mirror Reviewed

    Yuya Kubota, Hiroto Motoyama, Gota Yamaguchi, Satoru Egawa, Yoko Takeo, Masaki Mizuguchi, Himanshu Sharma, Shigeki Owada, Kensuke Tono, Hidekazu Mimura, Iwao Matsuda, Makina Yabashi

    Applied Physics Letters   Vol. 117 ( 4 ) page: 042405 - 042405   2020.7

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    DOI: 10.1063/5.0012348

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  6. Epitaxial L10-FeNi films with high degree of order and large uniaxial magnetic anisotropy fabricated by denitriding FeNiN films Reviewed

    Keita Ito, Masahiro Hayashida, Hiroto Masuda, Takahiro Nishio, Sho Goto, Hiroaki Kura, Tomoyuki Koganezawa, Masaki Mizuguchi, Yusuke Shimada, Toyohiko J. Konno, Hideto Yanagihara, Koki Takanashi

    Applied Physics Letters   Vol. 116 ( 24 ) page: 242404 - 242404   2020.6

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    DOI: 10.1063/5.0011875

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  7. Anomalous Nernst effect in Co-x(MgO)(1-x) granular thin films Reviewed

    P. Sheng, T. Fujita, M. Mizuguchi

    APPLIED PHYSICS LETTERS   Vol. 116 ( 14 ) page: 142403   2020.4

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    Authorship:Last author   Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER INST PHYSICS  

    The anomalous Nernst effect (ANE) is investigated for 100nm Co-x(MgO)(1-x) granular films as a function of the Co volume fraction (x) changes. The results show that by slightly adding MgO into the Co matrix, the anomalous Nernst angle (theta(AN)) can be largely enhanced more than three times compared with that of pure Co, which also results in the obvious change in ANE voltage. The transverse conductivity sigma XYA sigma XX shows distinct linear behavior in three regimes, which indicates different anomalous Hall effect (AHE) mechanisms. By qualitative Mott-relation analysis, we found that the non-monotonic dependence of ANE on x is associated with the change in AHE mechanisms.

    DOI: 10.1063/1.5140461

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  8. Perpendicular magnetic anisotropy of (001)-textured poly-crystalline MnAlGe films Reviewed

    Takahide Kubota, Yohei Kota, Keita Ito, Rie Y. Umetsu, Mingling Sun, Masaki Mizuguchi, Koki Takanashi

    AIP ADVANCES   Vol. 10 ( 1 )   2020.1

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    Cu2Sb-type intermetallic compound, MnAlGe, is known to exhibit uniaxial magnetocrystalline anisotropy and relatively small saturation magnetization, which is suitable for spintronic application, e.g. spin-transfer phenomena requiring small critical current density. Ge-concentration dependence of the crystal structures, saturation magnetization, M-s, and perpendicular magnetic anisotropy, K-u was investigated for MnAlGe films prepared onto silicon substrates with a thermally oxidized amorphous layer. For the stoichiometric and Ge-rich samples, the films exhibited (001)-texture with perpendicular magnetization. The maximum values of M-s and K-u were 270 emu/cm(3) and 4.8 x 106 erg/cm(3), respectively, which were comparable values with those reported for bulk and epitaxially grown films in literatures. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

    DOI: 10.1063/1.5130388

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  9. Non-chemical fluorination of hexagonal boron nitride by high-energy ion irradiation Reviewed

    S. Entani, K. V. Larionov, Z. I. Popov, M. Takizawa, M. Mizuguchi, H. Watanabe, S. Li, H. Naramoto, P. B. Sorokin, S. Sakai

    Nanotechnology   Vol. 31 ( 12 )   2020

  10. Different magnetic field effects on the ϵ-τ Phase transformation between (mn,zn)-al and mn-al-c Reviewed

    Yoshifuru Mitsui, Ryota Kobayashi, Yudai Takanaga, Akio Takaki, Rie Y. Umetsu, Kohki Takahashi, Masaki Mizuguchi, Keiichi Koyama

    IEEE Transactions on Magnetics   Vol. 55 ( 2 )   2019.2

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    © 1965-2012 IEEE. In-magnetic-field annealing (IFA) effects on Zn-modified Mn-Al and Mn-Al-C were investigated at the annealing temperature of 573 K, which was around their $_Rftxt-{\mathrm {C } }$. Mn53Zn2Al45 showed the magnetic-field-induced acceleration of the phase transformation to $\text{L}1-{0}$ -phase ( $\tau $ -phase) and the suppression of that to nonferromagnetic equilibrium phase. For Mn55Al45C2, IFA effects were not clearly detected. These different magnetic field effects were discussed by the difference of the mechanism in stabilization of $\tau $ -phase. It is found by a thermal analysis that the modification of Zn stabilized $\tau $ -phase against $\epsilon $ -phase, realizing acceleration of transformation to $\tau $ -phase. The addition of carbon stabilized $\epsilon $ -phase against $\tau $ -phase. The ineffectiveness of in-field annealing for Mn-Al-C is due to the stabilization of $\epsilon $ -phase and the reduction of the Curie temperature. The combination of Zn modification and IFA is realized to synthesize high fraction of $\tau $ -phase for short annealing time and low annealing temperature.

    DOI: 10.1109/TMAG.2018.2860559

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  11. The Accumulation of Heparan Sulfate S-Domains in Kidney Transthyretin Deposits Accelerates Fibril Formation and Promotes Cytotoxicity

    Kameyama H.

    American Journal of Pathology   Vol. 189 ( 2 ) page: 308 - 319   2019.2

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    DOI: 10.1016/j.ajpath.2018.09.015

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  12. "Fabrication of L10-FeNi by pulsed-laser deposition Reviewed

    M. Saito, H. Ito, Y. Suzuki, M. Mizuguchi, T. Koganezawa, T. Miyamachi, F. Komori, K. Takanashi, M. Kotsugi

    Applied Physics Letters   Vol. 114 ( 7 )   2019

  13. Anomaly in anomalous Nernst effect at low temperature for C1b-type NiMnSb half-Heusler alloy thin film Reviewed

    H. Sharma, Z. Wen, K. Takanashi, M. Mizuguchi

    Japanese Journal of Applied Physics   Vol. 58   2019

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    DOI: 10.7567/1347-4065/aafe68

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  14. Perpendicularly Magnetized Cu2Sb Type (Mn-Cr)AlGe Films onto Amorphous SiO2 Reviewed

    T. Kubota, Y. Kota, K. Ito, R. Umetsu, M. Sun, M. Mizuguchi, K. Takanashi

    Applied Physics Express   Vol. 12 ( 10 )   2019

  15. Magnetization reversal, damping properties and magnetic anisotropy of L10–ordered FeNi thin films Reviewed

    V. Thiruvengadam, B. B. Singh, T. Kojima, K. Takanashi, M. Mizuguchi, S. Bedanta

    Applied Physics Letters   Vol. 115 ( 20 )   2019

  16. FeNi and Fe16N2 Magnets Prepared Using Leaching Reviewed

    T. Kojima, S. Kameoka, M. Mizuguchi, K. Takanashi, A. P. Tsai

    Materials Transactions   Vol. 60 ( 6 ) page: 1066 - 1071   2019

  17. Fabrication of L10-type FeCo ordered structure using a periodic Ni buffer layer Reviewed

    H. Ito, M. Saito, T. Miyamachi, F. Komori, T. Koganezawa, M. Mizuguchi, M. Kotsugi

    AIP Advances   Vol. 9 ( 4 )   2019

  18. Fabrication of L10-FeNi films by denitriding FeNiN films Reviewed

    K. Ito, M. Hayashida, M. Mizuguchi, T. Suemasu, H. Yanagihara, K. Takanashi

    Journal of the Magnetics Society of Japan     2019

  19. Energy-harvesting materials based on the anomalous Nernst effect Invited Reviewed

    M. Mizuguchi, S. Nakatsuji

    Science and Technology of Advanced Materials   Vol. 20 ( 1 ) page: 262 - 275   2019

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    DOI: 10.1080/14686996.2019.1585143

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  20. Electronic structures of MgO/Fe interfaces with perpendicular magnetization revealed by hard X-ray photoemission with an applied magnetic field Reviewed

    S. Ueda, M. Mizuguchi, M. Tsujikawa, M. Shirai

    Science and Technology of Advanced Materials   Vol. 20 ( 1 ) page: 796 - 804   2019

  21. Control of anomalous Nernst effect in spintronic materials

    Mizuguchi Masaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 57 ( 9 )   2018.9

  22. Fabrication of L1(0)-FeNi phase by sputtering with rapid thermal annealing Reviewed

    Takayuki Tashiro, Masaki Mizuguchi, Takayuki Kojima, Tomoyuki Koganezawa, Masato Kotsugi, Takumi Ohtsuki, Kazuhisa Sato, Toyohiko Konno, Koki Takanashi

    JOURNAL OF ALLOYS AND COMPOUNDS   Vol. 750   page: 164 - 170   2018.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE SA  

    FeNi films were directly deposited on MgO(001) substrates by co-sputtering and rapid thermal annealing (RTA). The formation of the L1(0) phase was investigated for films with different thicknesses and different annealing conditions by grazing incidence X-ray diffraction. For the FeNi films with a thickness of 5 nm, superlattice 001 and 110 peaks were observed after annealing at a heating rate of 50 degrees C/s, which indicates that three variants of L1(0) grains were formed in the films. The maximum long-range order parameter, which corresponded to a volume-averaged parameter, was approximately 0.11. For the FeNi films with a thickness of 30 nm, a superlattice 110 peak was only observed after annealing at a heating rate of 50 degrees C/s, and the formation of 001 textured grains was clarified. Magnetic properties also changed depending on the FeNi film structures. The formation mechanism of L1(0)-FeNi is discussed based on the strain caused by RTA in the FeNi films. (C) 2018 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jallcom.2018.02.318

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  23. X-ray magnetic circular dichroism and hard X-ray photoelectron spectroscopy of tetragonal Mn72Ge28 epitaxial thin film Reviewed

    Jinhyeok Kim, Masaki Mizuguchi, Nobuhito Inami, Tetsuro Ueno, Shigenori Ueda, Koki Takanashi

    Japanese Journal of Applied Physics   Vol. 57 ( 4 )   2018.4

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    An epitaxially grown Mn72Ge28 film with a tetragonal crystal structure was fabricated. It was clarified that the film had a perpendicular magnetization and a high perpendicular magnetic anisotropy energy of 14.3 Merg/cm3. The electronic structure was investigated by X-ray magnetic circular dichroism and hard X-ray photoelectron spectroscopy. The obtained X-ray magnetic circular dichroism spectrum revealed that the Mn orbital magnetic moment governed the magnetocrystalline anisotropy of the Mn72Ge28 film. A doublet structure was observed for the Mn 2p3/2 peak of hard X-ray photoelectron spectrum, indicating the spin exchange interaction between the 2p core-hole and 3d valence electrons.

    DOI: 10.7567/JJAP.57.04FN10

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  24. MYRF is associated with encephalopathy with reversible myelin vacuolization

    Kurahashi H.

    Annals of Neurology   Vol. 83 ( 1 ) page: 98 - 106   2018.1

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    Publisher:Annals of Neurology  

    DOI: 10.1002/ana.25125

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  25. Focus on Advanced Materials for Energy Harvesting -Prospects and Approaches of Energy Harvesting Technologies- Reviewed

    H. Akinaga, H. Fujita, M. Mizuguchi, T. Mori

    Science and Technology of Advanced Materials   Vol. 19 ( 1 ) page: 543 - 544   2018

  26. Valence Sensitive X-ray Fluorescence Holography of Fe3O4 Reviewed

    A. K. R. Ang, T. Matsushita, Y. Hashimoto, N. Happo, Y. Yamamoto, M. Mizuguchi, A. Sato-Tomita, N. Shibayama, Y. C. Sasaki, K. Kimura, M. Taguchi, H. Daimon, K. Hayashi

    Physica Status Solidi (b)   Vol. 255 ( 11 )   2018

  27. Fabrication and characterization of L1(0)-ordered FeNi thin films Reviewed

    Koki Takanashi, Masaki Mizuguchi, Takayuki Kojima, Takayuki Tashiro

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 50 ( 48 )   2017.12

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    L1(0)-ordered FeNi, showing high uniaxial magnetic anisotropy (K-u), is promising as a 'rare metal-free' high K-u material. We have worked on L1(0)-ordered FeNi thin films prepared by two methods: one is molecular beam epitaxy (MBE) with alternate deposition of Fe and Ni monatomic layers, and the other is sputtering with co-deposition or multilayer-deposition of Fe and Ni followed by rapid thermal annealing (RTA). For the MBE films prepared by alternate monatomic layer deposition (leading to the stoichiometric composition: Fe 50 at.%-Ni 50 at.%), a clear relationship between K-u and the long-range order parameter S estimated by synchrotron x-ray diffraction (XRD) was found with maximum values of S = 0.48 and K-u = 7.0 x 10(6) erg cm(-3). The composition dependence of K-u was also investigated by deviating the thickness from monatomic layer, showing a maximum of 9.3 x 10(6) erg cm(-3) around 60 at.% Fe. In addition, the effect of Co addition to L1(0)-ordered FeNi was investigated, suggesting that a small amount (< 10 at.%) of Co substitution for Ni would enhance K-u if S keeps the same. The experiments were in qualitatively good agreement with the first-principles calculations. The magnetic damping constant a was also measured to be approximately 0.01 irrespective of S, suggesting that L1(0)-FeNi is a candidate material with high K-u and low a. For the sputtered films with RTA, no major difference between co-deposition and multilayer-deposition was found: in both cases the formation of L1(0)-ordered phase after RTA was definitely confirmed by XRD. Transmission electron microscopy observations indicated that nanometer-sized L1(0)-ordered clusters were dispersed in a disordered phase, in contrast to that of MBE films showing the homogeneous formation of L1(0)-ordered phase. The enhancement of coercivity (H-c) and residual magnetization (M-r/M-s) was observed associated with the appearance of L1(0)-ordered phase. The maxima of H-c and M-r/M-s were obtained to be 1.35 kOe and 0.22, respectively.

    DOI: 10.1088/1361-6463/aa8ff6

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  28. Synthesis of single-phase L1(0)-FeNi magnet powder by nitrogen insertion and topotactic extraction Reviewed

    Sho Goto, Hiroaki Kura, Eiji Watanabe, Yasushi Hayashi, Hideto Yanagihara, Yusuke Shimada, Masaki Mizuguchi, Koki Takanashi, Eiji Kita

    SCIENTIFIC REPORTS   Vol. 7   2017.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:NATURE PUBLISHING GROUP  

    Tetrataenite (L1(0)-FeNi) is a promising candidate for use as a permanent magnet free of rare-earth elements because of its favorable properties. In this study, single-phase L1(0)-FeNi powder with a high degree of order was synthesized through a new method, nitrogen insertion and topotactic extraction (NITE). In the method, FeNiN, which has the same ordered arrangement as L1(0)-FeNi, is formed by nitriding A1-FeNi powder with ammonia gas. Subsequently, FeNiN is denitrided by topotactic reaction to derive single-phase L1(0)-FeNi with an order parameter of 0.71. The transformation of disordered-phase FeNi into the L1(0) phase increased the coercive force from 14.5 kA/m to 142 kA/m. The proposed method not only significantly accelerates the development of magnets using L1(0)-FeNi but also offers a new synthesis route to obtain ordered alloys in non-equilibrium states.

    DOI: 10.1038/s41598-017-13562-2

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  29. Dependence of anomalous Nernst effect on crystal orientation in highly ordered gamma '-Fe4N films with anti-perovskite structure Reviewed

    Shinji Isogami, Koki Takanashi, Masaki Mizuguchi

    APPLIED PHYSICS EXPRESS   Vol. 10 ( 7 )   2017.7

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    The anomalous Nernst effect (ANE) in highly ordered Fe4N films was examined in the measurement configuration with an in-plane temperature gradient (del T-x). The anomalous Nernst coefficient (Q(s)) in the case of del T-x parallel to Fe4N[110] was clearly larger than that in the case of del x parallel to Fe4N[100]. Note here that no reports on the Q(s) in Fe4N films have been presented. This anisotropic Q(s) (Q(ani)) was also observed in a different configuration with an out-of-plane temperature gradient. Unlike Fe4N, pure Fe and A2-FeAl systems showed a negligible Q(ani). This Q(ani) might be attributed to the specific hybridization effects between the 3d orbitals of Fe and the 2p orbitals of N. (C) 2017 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.10.073005

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  30. Effects of Annealing Temperature and Magnetic Field on the ϵ-τ Phase Transformation in Mn-Al Alloys Reviewed

    Ryota Kobayashi, Yoshifuru Mitsui, Rie Y. Umetsu, Kohki Takahashi, Masaki Mizuguchi, Keiichi Koyama

    IEEE Magnetics Letters   Vol. 8   2017

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    © 2010-2012 IEEE. Magnetic field effects on the transformation from the hexagonal close-packed ϵ-phase to the ferromagnetic L10 τ-phase were evaluated for Mn-Al alloys annealed at 573, 623 and 673 K in magnetic fields up to 15 T. The phase transformation from the ϵ-phase to the τ-phase was enhanced by the magnetic field for the 623 K annealing temperature. These in-field annealing effects are explained by the Zeeman energy of the ferromagnetic τ -phase.

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  31. Magnetic-Field-Induced Acceleration of Phase Formation in tau-Mn-Al Reviewed

    Ryota Kobayashi, Yoshifuru Mitsui, Rie Y. Umetsu, Kohki Takahashi, Masaki Mizuguchi, Keiichi Koyama

    MATERIALS TRANSACTIONS   Vol. 58 ( 11 ) page: 1511 - 1518   2017

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    The phase formation of ferromagnetic L1(0)-MnAl (tau-phase) was accelerated by annealing in magnetic field. With in-field annealing at 623 K, the magnetization of the t-phase annealed at 15 T was a maximum of 72.2 A.m(2)/kg at 1.5 T, which is over 4 times larger than that annealed without an external magnetic field for the same annealing time. On the other hand, the transformation from tau-phase to beta-phase was suppressed under magnetic field. The obtained bulk sample did not show magnetic anisotropy because of the epsilon-tau solid-state transformation. Obtained results suggested that magnetic field induced acceleration of transformation was due to the gain of Zeeman energy, which increases the driving force of the epsilon-tau transformation.

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  32. Microstructural evolution and correlated magnetic domain configuration of nanoparticles embedded in a single crystal of Cu-75-Ni-20-Fe-5 alloy Reviewed

    Jun-Seop Kim, Toshiyuki Taniuchi, Masaki Mizuguchi, Shik Shin, Koki Takanashi, Mahoto Takeda

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 49 ( 33 )   2016.8

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    We have investigated the microstructural evolution and magnetic domain configurations in nano-scale Fe-Ni rich precipitates formed in a single-crystal specimen of Cu-20at%Ni-5at%Fe alloy on isothermal annealing at 873 K and 973 K, using a combination of transmission electron microscopy (TEM), electron backscattering diffraction, field-emission scanning electron microscopy (FE-SEM), and laser-based photoemission electron microscopy (laser-PEEM). The TEM and FE-SEM observations showed that small, spherical solute-rich particles formed randomly in the initial stage of the precipitation, but on isothermal annealing, cubic, rectangular, plate-shaped and rod-shaped precipitates appeared and aligned along the < 1 0 0 > directions in the copper-rich matrix. Laser-PEEM was applied to single-crystal specimens of the alloy and allowed direct observations of magnetic domain configurations in individual ferromagnetic particles at the nanometer scale. This revealed that cubic particles of size approximately 50-60 nm consist of single magnetic domains, but particles of size 100 nm have a closed spin structure (e.g. vortex or multiple domains).

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  33. Electronic structure and magnetic anisotropy of L1(o)-FePt thin film studied by hard x-ray photoemission spectroscopy and first-principles calculations Reviewed

    S. Ueda, M. Mizuguchi, Y. Miura, J. G. Kang, M. Shirai, K. Takanashi

    APPLIED PHYSICS LETTERS   Vol. 109 ( 4 )   2016.7

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    We have studied the electronic structure of the L1(o) ordered FePt thin film by hard x-ray photoemission spectroscopy (HAXPES), cluster model, and first-principles calculations to investigate the relationship between the electronic structure and perpendicular magneto-crystalline anisotropy (MCA). The Fe 2p core-level HAXPES spectrum of the ordered film revealed the strong electron correlation in the Fe 3d states and the hybridization between the Fe 3d and Pt 5d states. By comparing the experimental valence band structure with the theoretical density of states, the strong electron correlation in the Fe 3d states modifies the valence band electronic structure of the L1(o) ordered FePt thin film through the Fe 3d-Pt 5d hybridization. These results strongly suggest that the strong electron correlation effect in the Fe 3d states and the Fe 3d-Pt 5d hybridization as well as the spin-orbit interaction in the Pt 5d states play important roles in the perpendicular MCA for L1(o)-FePt. Published by AIP Publishing.

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  34. Growth of L1(0)-FeNi thin films on Cu(001) single crystal substrates using oxygen and gold surfactants Reviewed

    Takayuki Kojima, Masaki Mizuguchi, Koki Takanashi

    THIN SOLID FILMS   Vol. 603   page: 348 - 352   2016.3

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    We alternately deposited Ni and Fe monatomic layers on Cu(001) single crystal substrates and also performed surfactant-mediated growth. FeNi films exhibited a large uniaxial magnetic anisotropy (K-u) of over 0.1 MJ/m(3) by using an oxygen or a gold surfactant, although K-u was almost zero without surfactants. Reflection high-energy electron diffraction and atomic force microscopy indicated surfactant effects of oxygen and gold. Synchrotron X-ray diffraction indicated a formation of an L1(o)-type ordered FeNi phase having a large K-u. We have considered that the surfactants enhanced layer-by-layer growth leading to the L1(o)-ordering by changing a diffusion scenario of Fe and Ni atoms. (C) 2016 Elsevier B.V. All rights reserved.

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  35. Temperature dependence of enhanced spin relaxation time in metallic nanoparticles: Experiment and theory Reviewed

    T. Koda, S. Mitani, S. Takahashi, M. Mizuguchi, K. Sato, T. J. Konno, S. Maekawa, K. Takanashi

    PHYSICAL REVIEW B   Vol. 93 ( 8 )   2016.2

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    We study the enhanced spin relaxation time of Au nanoparticles in nanopillar-shaped double-barrier junction devices with a stacked Fe/MgO/Au-nanoparticle/MgO/Fe structure. The size of Au nanoparticles located in a current path is deduced from a transmission electron micrograph and the Coulomb blockade behavior in the current-voltage characteristics of the devices. A finite tunnel magnetoresistance (TMR) is observed above a critical current and is attributable to spin accumulation in Au nanoparticles. Based on a simple model of TMR due to spin accumulation in a nanoparticle, the spin relaxation time tau(s) is estimated from the magnitude of the critical current. The temperature and bias-voltage region where TMR appears are determined from systematic observations, showing that the appearance of TMR is not associated with the Coulomb blockade but with spin accumulation. We find that the obtained tau(s) is anomalously extended (similar to 800 ns) at low temperatures and abruptly decreases above a critical temperature. Interestingly, the critical temperature strongly depends on the size of the Au nanoparticles and is much lower than the effective temperature corresponding to the discrete energy spacing. A theoretical analysis for the spin relaxation of electrons with discrete energy levels shows that not only the anomalously extended spin relaxation time, but also the strong temperature dependence of tau(s) arise from the broadening of discrete energy levels due to coupling with phonons in the surrounding matrix. Numerical calculations using reasonable parameter values well reproduce the observed temperature and size dependence of the spin relaxation time in Au nanoparticles.

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  36. Anomalous Nernst effect in epitaxial Co/Ni multilayer films

    Mizuguchi Masaki, Suzuki Hidenobu, Takanashi Koki

    Meeting Abstracts of the Physical Society of Japan   Vol. 71   page: 925 - 925   2016

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    DOI: 10.11316/jpsgaiyo.71.2.0_925

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  37. Effective fluorination of single-layer graphene by high-energy ion irradiation through a LiF overlayer Reviewed

    Shiro Entani, Masaki Mizuguchi, Hideo Watanabe, Liubov Yu. Antipina, Pavel B. Sorokin, Pavel V. Avramov, Hiroshi Naramoto, Seiji Sakai

    RSC ADVANCES   Vol. 6 ( 72 ) page: 68525 - 68529   2016

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    A new non-chemical method for heteroatom doping into single-layer graphene was demonstrated by high-energy ion irradiation of the graphene-based heterostructure. The heterostructure was fabricated by depositing a LiF layer on a single-layer graphene sheet which was grown on a Cu substrate by chemical vapor deposition. We successfully obtained fluorinated graphene by 2.4 MeV Cu-63(2+) ion irradiation through the LiF overlayer. Raman spectroscopy, near edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy revealed that 20%-fluorinated graphene is obtained superior to the defect formation by the high-energy ion irradiation up to 1014 ions per cm(2). It was also shown that the F atoms are chemically adsorbed on single-layer graphene by the C-F bonds in a similar manner to the fluorinated graphene synthesized by the purely chemical route. The mechanism of the fluorination by the ion irradiation is discussed in terms of electronic excitations of carbon and heteroatoms based on the spectroscopic results.

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  38. Structural and Magnetic Depth Profile Analysis of L10 FeNi Film by Polarized Neutron Reflectometry Reviewed

    Tetsuro Ueno, Kotaro Saito, Nobuhito Inami, Takayuki Kojima, Masaki Mizuguchi, Noboru Miyata, Kazuhiro Akutsu, Masayasu Takeda, Koki Takanashi, Kanta Ono

    JPS Conference Proceedings   Vol. 8   page: 034008   2015.9

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    DOI: 10.7566/JPSCP.8.034008

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  39. Material dependence of anomalous Nernst effect in perpendicularly magnetized ordered-alloy thin films Reviewed

    K. Hasegawa, M. Mizuguchi, Y. Sakuraba, T. Kamada, T. Kojima, T. Kubota, S. Mizukami, T. Miyazaki, K. Takanashi

    APPLIED PHYSICS LETTERS   Vol. 106 ( 25 )   2015.6

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    Material dependence of the anomalous Nernst effect (ANE) in perpendicularly magnetized ordered-alloy thin films is systematically investigated. The ANE was found to have a tendency to increase simply as uniaxial magnetic anisotropy increased at room temperature. The ANE increases as temperature increases from 10 to 300K for all the materials. However, the signs of the ANE in Fe-based ordered-alloys (L1(0)-FePt and L1(0)-FePd) and in a Co/Ni multilayer are opposite to those in Mn-based ordered-alloys (L1(0)-MnGa and D0(22)-Mn2Ga). Ordered-alloys with larger uniaxial magnetic anisotropies reveal larger ANE and might be desirable for thermoelectric applications. (C) 2015 AIP Publishing LLC.

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  40. Local structure and magnetism of L1(0)-type FeNi alloy films with perpendicular magnetic anisotropy studied through Fe-57 nuclear probes Reviewed

    K. Mibu, T. Kojima, M. Mizuguchi, K. Takanashi

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 48 ( 20 )   2015.5

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    The local structure and magnetism of FeNi alloy films prepared by alternate deposition of Fe and Ni monatomic layers, where perpendicular magnetic anisotropy has been observed, were investigated through Fe-57 nuclear probes using Mossbauer spectroscopy. It was confirmed that the films are composed of L1(0)-type ordered FeNi phase and A1-type disordered FeNi phase. For the films grown at 40-70 degrees C, which have no perpendicular anisotropy, the A1-disordered phase is dominant, whereas for the films grown at 100-190 degrees C, which have a stronger perpendicular anisotropy, the relative amount of the L1(0)-ordered phase reaches 40% or more. It was clearly shown that the magnetic anisotropy of these films is strongly correlated with the local environments of Fe in the films. The results imply that if a further increase in the ratio of the L1(0)-ordered phase is successfully achieved, one would obtain films with a stronger magnetic anisotropy applicable to perpendicular magnetic recording.

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  41. Structural and magnetic properties of FeNi thin films fabricated on amorphous substrates Reviewed

    T. Y. Tashiro, M. Mizuguchi, T. Kojima, T. Koganezawa, M. Kotsugi, T. Ohtsuki, K. Takanashi

    JOURNAL OF APPLIED PHYSICS   Vol. 117 ( 17 )   2015.5

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    FeNi films were fabricated by sputtering and rapid thermal annealing on thermally amorphous substrates to realize the formation of an L1(0)-FeNi phase by a simple method. Structural and magnetic properties of FeNi films were investigated by varying the annealing temperature. L1(0)-FeNi superlattice peaks were not observed in X-ray diffraction patterns, indicating no formation of L1(0)-ordered phase, however, the surface structure systematically changed with the annealing temperature. Magnetization curves also revealed a drastic change depending on the annealing temperature, which indicates the close relation between the morphology and magnetic properties of FeNi films fabricated on amorphous substrates. (C) 2015 AIP Publishing LLC.

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  42. Comparison of electrical and optical detection of spin injection in L1(0)-FePt/MgO/GaAs hybrid structures Reviewed

    R. Ohsugi, J. Shiogai, Y. Kunihashi, M. Kohda, H. Sanada, T. Seki, M. Mizuguchi, H. Gotoh, K. Takanashi, J. Nitta

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 48 ( 16 )   2015.4

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    We have investigated comparative experiments for spin injection into semiconductor in an ordered L1(0)-FePt/MgO/n-GaAs hybrid structure using electrical and optical detection methods. Spatial-resolved Kerr rotation microscope image clearly demonstrates accumulation of perpendicularly oriented spins in an n-GaAs channel at zero magnetic field. On the other hand, electrical three-terminal Hanle measurement shows shorter spin lifetime than that of the optical measurement. It suggests that the spin lifetime obtained from three-terminal Hanle method originates from spins at the MgO/GaAs interface but not in the bulk GaAs channel.

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  43. Cu75-Ni20-Fe5合金単結晶における微視的組織と磁気特性 Reviewed

    金俊燮, 水口将輝, 竹田真帆人

    銅と銅合金     2015

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  44. Addition of Co to L1(0)-ordered FeNi films: influences on magnetic properties and ordered structures Reviewed

    Takayuki Kojima, Masaki Mizuguchi, Tomoyuki Koganezawa, Misako Ogiwara, Masato Kotsugi, Takumi Ohtsuki, Taka-Yuki Tashiro, Koki Takanashi

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 47 ( 42 )   2014.10

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    L1(0)-type ordered FeNi alloy is a good candidate material for rare-earth-free permanent magnets due to its large saturation magnetization, large uniaxial magnetic anisotropy (K-u) and high Curie temperature. Previously, we investigated the fundamental properties of L1(0)-FeNi by preparing single crystal films by alternate deposition of Fe and Ni monatomic layers. In the present study, we investigated the influences of the addition of Co on the magnetic and structural properties of L1(0)-type ordered FeNi films. Three types of Co addition, with the substitution of Fe layers, Ni layers and both layers, were performed. X-ray diffraction using synchrotron radiation indicated that Co atoms were randomly distributed in films in all addition processes. A long-range order parameter of the L1(0)-FeNi phase and K-u showed a tendency to decrease with the amount of Co for additions substituting Fe layers and both layers. However, K-u showed no decrease with Co addition substituting <= 10% of Ni layers, even though the order parameter notably decreased. This indicates that an achievement of the Co addition substituting Ni atoms without any reduction of the order parameter enhances K-u in L1(0)-FeNi.

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  45. Formation of FeNi with L1(0)-ordered structure using high-pressure torsion Reviewed

    Seungwon Lee, Kaveh Edalati, Hideaki Iwaoka, Zenji Horita, Takumi Ohtsuki, Takuo Ohkochi, Masato Kotsugi, Takayuki Kojima, Masaki Mizuguchi, Koki Takanashi

    PHILOSOPHICAL MAGAZINE LETTERS   Vol. 94 ( 10 ) page: 639 - 646   2014.10

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    FeNi with the L1(0)-ordered structure is formed over an astronomical timescale in meteorites. In this study, severe plastic deformation using high-pressure torsion (HPT) is employed for the production of the L1(0) structure in the laboratory. Its formation is confirmed by X-ray diffraction analysis and transmission electron microscopy. Processing of elemental nanopowders by HPT is an effective method for the formation of the L1(0) phase, which is enhanced by the addition of Co to FeNi or annealing after HPT. The formation of the phase must be associated with enhanced diffusion through HPT.

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  46. Detection of spin-resolved electronic structures from a buried ferromagnetic layer utilizing forward Mott scattering Reviewed

    S. Ueda, M. Mizuguchi, T. Kojima, S. Ishimaru, M. Tsujikawa, M. Shirai, K. Takanashi

    APPLIED PHYSICS LETTERS   Vol. 104 ( 13 )   2014.3

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    We report ultrahigh-resolution spin-resolved hard X-ray photoemission (HAXPES) for a buried FeNi alloy film. By utilizing the forward Mott scattering in a Au layer on FeNi, our spin-resolved HAXPES method does not require a standard spin detector and allows us to use the multi-channel electron detection system for the high-efficient electron detection as used in conventional photoemission spectroscopy. A combination of the forward Mott scattering and multi-channel detection leads us to measure a clear spin polarization as well as spin-resolved majority and minority states in the Fe 2p core-level spectra without using the standard spin detector. This method enables us to measure spin-resolved core-level spectra for buried ferromagnetic materials. (C) 2014 AIP Publishing LLC.

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  47. 064206Structural, magnetic and electronic state characterization of L1(0)-type ordered FeNi alloy extracted from a natural meteorite Reviewed

    M. Kotsugi, H. Maruyama, N. Ishimatsu, N. Kawamura, M. Suzuki, M. Mizumaki, K. Osaka, T. Matsumoto, T. Ohkochi, T. Ohtsuki, T. Kojima, M. Mizuguchi, K. Takanashi, Y. Watanabe

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 26 ( 6 )   2014.2

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    To understand the hard magnetism of L1(0)-type ordered FeNi alloy, we extracted the L1(0)-FeNi phase from a natural meteorite, and evaluated its fundamental solid-state properties: sample composition, magnetic hysteresis, crystal structure and electronic structure. We executed multidirectional analyses using scanning electron microscopy with an electron probe micro-analyzer (SEM-EPMA), a superconducting quantum interference device (SQUID), x-ray diffraction (XRD) and magnetic circular dichroism (MCD). As a result, we found that the composition was Fe: 50 : 47 +/- 1 : 98 at.%, Ni: 49 : 60 +/- 1 : 49 at.%, and an obvious superlattice peak is confirmed. The estimated degree of order was 0.608, with lattice constants a = b = 3 : 582 angstrom and c = 3 : 607 angstrom. The obtained coercivity was more than 500 Oe. MCD analysis using the K absorption edge suggests that the magnetic anisotropy could originate from the orbital magnetic moment of 3d electrons in Fe; this result is consistent with that in a previous report obtained with synthetic L1(0)-FeNi.

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  48. Fe-Ni composition dependence of magnetic anisotropy in artificially fabricated L1(0)-ordered FeNi films Reviewed

    Takayuki Kojima, Misako Ogiwara, Masaki Mizuguchi, Masato Kotsugi, Tomoyuki Koganezawa, Takumi Ohtsuki, Taka-Yuki Tashiro, Koki Takanashi

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 26 ( 6 )   2014.2

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    We prepared L1(0)-ordered FeNi alloy films by alternate deposition of Fe and Ni monatomic layers, and investigated their magnetic anisotropy. We employed a non-ferromagnetic Au-Cu-Ni buffer layer with a flat surface and good lattice matching to L1(0)-FeNi. An L1(0)-FeNi film grown on Au6Cu51Ni43 showed a large uniaxial magnetic anisotropy energy (K-u = 7.0 x 10(6) erg cm(-3)). K-u monotonically increased with the long-range order parameter ( S) of the L1(0) phase. We investigated the Fe-Ni composition dependence by alternating the deposition of Fe 1 - x and Ni 1 + x monatomic layers ( -0.4 < x < 0.4). Saturation magnetization (M-s) and K-u showed maxima (M-s = 1470 emu cm(-3), K-u = 9.3 x 10(6) erg cm (-3)) for Fe60Ni40 (x = -0.2) while S showed a maximum at the stoichiometric composition (x = 0). The change in the ratio of lattice parameters (c/a) was small for all compositions. We found that enrichment of Fe is very effective to enhance Ku. The large Ms and Ku of Fe60Ni40 indicate that Fe-rich L10-FeNi is promising as a rare-earth-free permanent magnet.

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  49. Magnetic domain observation of FeCo thin films fabricated by alternate monoatomic layer deposition Reviewed

    T. Ohtsuki, T. Kojima, M. Kotsugi, T. Ohkochi, M. Mizuguchi, K. Takanashi

    JOURNAL OF APPLIED PHYSICS   Vol. 115 ( 4 )   2014.1

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    FeCo thin films are fabricated by alternate monoatomic layer deposition method on a Cu3Au buffer layer, which in-plane lattice constant is very close to the predicted value to obtain a large magnetic anisotropy constant. The variation of the in-plane lattice constant during the deposition process is investigated by reflection high-energy electron diffraction. The magnetic domain images are also observed by a photoelectron emission microscope in order to microscopically understand the magnetic structure. As a result, element-specific magnetic domain images show that Fe and Co magnetic moments align parallel. A series of images obtained with various azimuth reveal that the FeCo thin films show fourfold in-plane magnetic anisotropy along < 110 > direction, and that the magnetic domain structure is composed only of 90 degrees wall. (C) 2014 AIP Publishing LLC.

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  50. Significant surface flattening effect by Au addition for Cu growth on Cu3Au(001) Reviewed

    Takayuki Kojima, Masaki Mizuguchi, Koki Takanashi

    SURFACE SCIENCE   Vol. 619   page: 44 - 48   2014.1

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    To prepare a flat surface of Cu film on Cu3Au(001), we utilized the effect of Au addition to Cu, and investigated the dependence of the growth mode on the amount of Au added. We grew Cu-x%Au (x = 0-20) films on Cu3Au(001) underlayers by co-deposition and observed the surface morphology by scanning tunneling microscopy. For Cu film without Au addition, three-dimensional islands were observed on the surface while flat two-dimensional surfaces were observed for Cu film with only 2.5%Au addition. This difference in the growth mode was found to be due to surface segregation of Au revealed by in situ Auger electron spectroscopy. It was considered that the Au atoms acted like a surfactant and avoided three-dimensional island growth by suppression of the accumulation of epitaxial strain in Cu-x%Au films. However, the terrace size decreased with x. This decrease was thought to be due to an increase in an effective Ehrlich-Schwoebel barrier. The surface flattening effect by addition of another element would be obtained in other systems as well by employing a suitable element. (C) 2013 Elsevier B.V. All rights reserved.

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  51. Magnetization damping of an L1(0)-FeNi thin film with perpendicular magnetic anisotropy Reviewed

    Misako Ogiwara, Satoshi Iihama, Takeshi Seki, Takayuki Kojima, Shigemi Mizukami, Masaki Mizuguchi, Koki Takanashi

    APPLIED PHYSICS LETTERS   Vol. 103 ( 24 )   2013.12

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    We studied on the magnetic damping constants (alpha) for L1(0)-FeNi and disordered FeNi employing three kinds of measurement methods. An L1(0)-FeNi thin film exhibited high perpendicular magnetic anisotropy of 7.1 x 10(6) erg cm(-3). At magnetic fields (H) lower than 2 kOe, alpha was estimated to be 0.091 +/- 0.003. However, it was reduced down to 0.013 +/- 0.001 with H, indicating that extrinsic contributions enhance alpha. The intrinsic alpha = 0.013 +/- 0.001 was comparable to alpha = 0.009 +/- 0.002 for the disordered FeNi. This suggests that L1(0)-FeNi is a candidate achieving high magnetic anisotropy and low magnetization damping simultaneously. (C) 2013 AIP Publishing LLC.

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  52. Ion-irradiation enhancement of materials degradation in Fe-Cr single crystals detected by magnetic technique Reviewed

    Yasuhiro Kamada, Hideo Watanabe, Seiji Mitani, Jitendra Narayana Mohapatra, Hiroaki Kikuchi, Satoru Kobayashi, Masaki Mizuguchi, Koki Takanashi

    JOURNAL OF NUCLEAR MATERIALS   Vol. 442 ( 1-3 ) page: S861 - S864   2013.11

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    Single crystalline Fe-20% Cr film was prepared using a molecular beam epitaxy technique, and 2.4 MeV Cu2+ ion-irradiation was subsequently carried out at room temperature and at 748 K. Magnetic hysteresis measurement and magnetic domain observation showed that room-temperature irradiation did not have a large effect on the magnetic properties of Fe-20% Cr films. However, irradiation at 748 K caused a significant magnetic hardening and a drastic change in domain structures. It is assumed that the domain characteristics reflect the formation of chromium-rich precipitates due to the phase separation accelerated by irradiation. This study demonstrates the feasibility of nondestructive magnetic techniques for evaluating the materials degradation of Fe-Cr alloys under the irradiation environment. (C) 2012 Elsevier B.V. All rights reserved.

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  53. Relationship between the microstructure and the magnetic properties of nano-scale magnetic particles formed in a Cu-10 at% Ni-5 at% Co alloy Reviewed

    Dong-Hae Lee, Takahiro Moriki, Mahoto Takeda, Sung Kang, Dong-Sik Bae, Masaki Mizuguchi, Koki Takanashi

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   Vol. 63 ( 3 ) page: 555 - 558   2013.8

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    Cu-10 at% Ni-5 at% Co specimens containing nano-scale magnetic particles were investigated with respect to the relationship between the microstructure and the magnetic properties, by using a transmission electron microscope (TEM), a SQUID magnetometer and a magnetic thermobalance. The present TEM observations revealed that small magnetic precipitates were formed in a copper matrix in a specific manner that has never been reported in conventional precipitation alloys consisting of non-magnetic elements. The SQUID measurements indicated that a specimen annealed for a short period had a large coercive force, although the force decreased for longer annealing treatments. The magnetic thermogravity scan in the temperature range of 300-1223 K showed that the alloy specimen had a paramagnetic state between two ferromagnetic regions.

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  54. Magneto-Optical Properties and Size Effect of Ferromagnetic Metal Nanoparticles Reviewed

    Terunori Kaihara, Masaki Mizuguchi, Koki Takanashi, Hiromasa Shimizu

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 52 ( 7 )   2013.7

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    We investigated the magneto-optical (MO) effect with localized surface plasmon resonance (LSPR) on ferromagnetic metal (Fe and Co) nanoparticles. We estimated the electric-field enhancement of the ferromagnetic metal nanoparticles caused by LSPR based on Mie scattering theory and compared it with that of Au nanoparticles. The electric-field enhancement of the ferromagnetic metal nanoparticles was 15-17, which is half of that of the Au nanoparticles. In order to explain the calculated results, we prepared ferromagnetic metal nanoparticles by a self-assembly process. We measured the optical transmission spectra and Faraday effect of the ferromagnetic nanoparticles. Although remarkable MO enhancement was not observed, we found characteristic MO spectra and a peak shift at wavelengths longer than 800 nm in samples whose thickness was less than 6 nm. We numerically investigated the size effect and reproduced the experimental results. We concluded that localized plasmons of ferromagnetic metal nanoparticles can produce electric-field enhancement, but the enhancement is not enough to increase the MO effect, and that the MO effect of nanosized ferromagnetic metals could be influenced by size effects rather than by LSPR. (C) 2013 The Japan Society of Applied Physics

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  55. Erratum: Anomalous nernst effect in an l10-ordered epitaxial fept thin film (Applied Physics Express (2012) 5 (093002)) Reviewed

    Masaki Mizuguchi, Satoko Ohata, Kota Hasegawa, Ken Ichi Uchida, Eiji Saitoh, Koki Takanashi

    Applied Physics Express   Vol. 6 ( 4 )   2013.4

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  56. Anomalous nernst effect in L10-FePt/MnGa thermopiles for new thermoelectric applications Reviewed

    Yuya Sakuraba, Kota Hasegawa, Masaki Mizuguchi, Takahide Kubota, Shigemi Mizukami, Terunobu Miyazaki, Koki Takanashi

    Applied Physics Express   Vol. 6 ( 3 )   2013.3

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    We propose a new-type of thermopile consisting of two ferromagnetic materials with anomalous Nernst effects (ANEs) of opposite signs. L1 0-FePt and L10-MnGa have been chosen as the materials because they show large ANEs with opposite signs. The combination of perpendicularly magnetized FePt and MnGa wires enhances the ANE voltage effectively. The ANE in in-plane magnetized FePt films induced by applying a perpendicular temperature difference shows no variation against the film thickness, which is a promising characteristic for thermoelectric applications because the internal resistance of the thermopile, which determines the extractable electric power, can be reduced by increasing the thickness of ferromagnetic wires. © 2013 The Japan Society of Applied Physics.

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  57. Origin of strong magnetic anisotropy in L1(0)-FeNi probed by angular-dependent magnetic circular dichroism Reviewed

    Masato Kotsugi, Masaki Mizuguchi, Shigeki Sekiya, Masaichiro Mizumaki, Takayuki Kojima, Tetsuya Nakamura, Hitoshi Osawa, Kenji Kodama, Takumi Ohtsuki, Takuo Ohkochi, Koki Takanashi, Yoshio Watanabe

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 326   page: 235 - 239   2013.1

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    We investigated the origin of strong magnetic anisotropy energy (MAE) in L1(0)-type ordered FeNi phase by angular-dependent magnetic circular dichroism. Our findings showed that the orbital magnetic moment of Fe has a significant angular dependence that exhibits a maximum value at the [001] direction corresponding perpendicular to the plane. The calculated uniaxial anisotropy energy when considering spin-orbit (SO) interaction shows quantitatively good agreement with the volume MAE. We concluded that the orbital anisotropy in 3d Fe electrons results in the strong MAE in L1(0)-FeNi and ascribe this to the spin-orbit interaction via structural ordering. (C) 2012 Elsevier BY. All rights reserved.

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  58. Fabrication of highly L10-ordered FePt thin films by low-temperature rapid thermal annealing Reviewed

    M. Mizuguchi, T. Sakurada, T. Y. Tashiro, K. Sato, T. J. Konno, K. Takanashi

    APL Materials   Vol. 1 ( 3 )   2013

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    Highly L10-ordered FePt thin films with a strong (001) texture were successfully fabricated on amorphous substrates simply by co-sputtering and rapid thermal annealing at a low temperature of 400â°C. The morphology of FePt thin films depended strongly on the heating rate, changing from a continuous structure with an atomically flat surface to an island-like structure. The change of the morphology resulted in a drastic increase of coercivity, indicating that the magnetization process could be controlled by the heating condition. This fabrication method of ordered FePt thin films is favorable in view of the compatibility for a practical device fabrication process. © 2013 Author(s).

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  59. Synthesis and Characterization of L10-FeNi Powders Reviewed

    Y. Hayashi, S. Gotou, M. Mizuguchi, M. Kotsugi, Y. Kitou, E. Okuno, K. Takanashi

    Journal of the Magnetics Society of Japan     2013

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  60. Direct imaging of atomic clusters in an amorphous matrix: A Co-C granular thin film Reviewed

    Kazuhisa Sato, Masaki Mizuguchi, Ruihe Tang, Jung-Goo Kang, Manabu Ishimaru, Koki Takanashi, Toyohiko J. Konno

    APPLIED PHYSICS LETTERS   Vol. 101 ( 19 )   2012.11

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    The atomic structure of extremely small cobalt (Co) nanoparticles embedded in an amorphous carbon (C) matrix has been studied by spherical aberration (C-s) corrected high-resolution transmission electron microscopy and focal-series restoration. The Co nanoparticles, 1-3 nm in diameter, are crystalline with the face centered cubic structure, while the radial distribution function analysis revealed the existence of a Co-C bond. The reconstructed phase images of the exit-wave function clearly show the projected potential distribution within the Co nanoparticles. The C-s-correction has hence a benefit to visualize embedded crystalline clusters unambiguously, which are responsible for the magnetotransport properties of the Co-C films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765362]

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  61. Low-Temperature Magnetotransport and Magnetic Properties of Cobalt-Doped Amorphous Carbon Thin Films Reviewed

    Tang Ruihe, Liu Wei, Zhang Zhengjun, Yu Ronghai, Liu Xiaofang, Yang Bai, Mizuguchi Masaki, Takanashi Koki

    RARE METAL MATERIALS AND ENGINEERING   Vol. 41 ( 11 ) page: 1887 - 1890   2012.11

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    A series of Co-doped amorphous carbon granular thin films with various Co contents (x, at%) were deposited on n-type Si (100) substrates by a magnetron co-sputtering technique at room temperature. The microstructure, magnetotransport and magnetic properties of the Co-C films have been characterized. By optimizing Co content, giant negative magnetoresistances (MRs) were observed at low temperature, with a maximum MR ratio of 27.6% at 2 K under an applied magnetic field of 90x79.6 kA.m(-1) for the film with Co content of 6.4 at%. As Co content increases from 6.4 at% to 16.4 at%, the MR ratio decreases gradually from 27.6% to 2.2%. A linear In rho-T-1/2 relationship indicates that the spin transport in Co6.4C93.6 thin film agrees well with tunneling conductance.

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  62. Simple Analysis for Frequency Increase in Spin Torque Oscillation Reviewed

    Chiharu Mitsumata, Satoshi Tomita, Takeshi Seki, Masaki Mizuguchi

    IEEE TRANSACTIONS ON MAGNETICS   Vol. 48 ( 11 ) page: 3955 - 3957   2012.11

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    The spin torque oscillation (STO) due to magnetic resonance is investigated in term of the Landau-Lifshitz-Gilbert (LLG) equation. An analytic formula of the LLG equation with macro-spins describes a spin state that involves information of an oscillation frequency. The LLG equation can be transformed into an equation of a forced oscillation. The obtained equation includes a frequency of STO, an effective Gilbert damping factor, and an injected spin current. We show that the effective Gilbert damping is given by a linear function of the spin current. Contrastingly, the frequency of STO is not affected by the injected spin current. However, the time-dependent variation of the spin current, e. g., the pulsated spin current, possibly increases the frequency of STO.

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  63. Anomalous nernst effect in an L1 <inf>0</inf>-ordered epitaxial FePt thin film Reviewed

    Masaki Mizuguchi, Satoko Ohata, Ken Ichi Uchida, Eiji Saitoh, Koki Takanashi

    Applied Physics Express   Vol. 5 ( 9 )   2012.9

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    The anomalous Nernst effect in a perpendicularly magnetized L1 0-ordered epitaxial FePt(001) thin film has been investigated, and the anomalous Nernst coefficient and the anomalous Nernst angle of the FePt thin film were experimentally evaluated. Furthermore, the voltage due to the anomalous Nernst effect in the spin-Hall device was simulated by the finite element method. A good agreement between the experiment and the simulation was found. It was revealed that the anomalous Nernst effect could be quantitatively discussed even in nanoscale devices. © 2012 The Japan Society of Applied Physics.

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  64. Barrier height imaging of magnetic films: Use for studying the initial growth of Co films and the surface structure of FePt films Reviewed

    T. Kawagoe, E. Wakabayashi, Y. Murasawa, T. Sakata, M. Mizuguchi, K. Takanashi

    SURFACE SCIENCE   Vol. 606 ( 3-4 ) page: 226 - 232   2012.2

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    Barrier-height (BH) imaging using scanning tunneling microscopy (STM) was used to study the growth of Co films on Au(001) surfaces. We have observed BH of metastable bcc Co film (&gt;1 ML) for the first time, and that showed a large BH value (similar to 6 eV), whereas the observed BH of the Au(001) surface (similar to 3.5 eV) was consistent with the previous results. The origin of the large BH was qualitatively understood by considering that 3d electrons for tunneling are dominant for the Co(001) surface. We have observed numerous islands with different sizes and heights after 0.15 ML Co coverage and successfully obtained, from the BH imaging, an element-specific contrast, i.e. recognizing aggregated Au islands and Co islands, and information about inhomogenities of BH with proper consideration of the artifacts near the step edges. The height modification by the large BH difference is discussed.
    STM/BH studies of FePt films revealed two kinds of monolayer heights, the sum which was equal to the c axis lattice constant of L1(O) FePt. Two different dl/dz signal levels were observed on atomically flat terraces. (C) 2011 Elsevier B.V. All rights reserved.

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  65. MgO Layer Thickness Dependence of Structure and Magnetic Properties of L1(0)-FePt/MgO/GaAs Structures Reviewed

    Rento Ohsugi, Makoto Kohda, Takeshi Seki, Akihiko Ohtsu, Masaki Mizuguchi, Koki Takanashi, Junsaku Nitta

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 51 ( 2 )   2012.2

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    We investigated the MgO layer thickness dependences of the structure and magnetic properties of L1(0)-FePt/MgO/GaAs structures. To examine how the crystallinity and growth morphology of the MgO layer affect the L1(0)-FePt layer, two kinds of preparation method were employed for MgO deposition: electron beam (EB) evaporation and sputter deposition. The MgO layer deposited by EB evaporation included a large strain because of the cube-on-cube epitaxial relationship despite a large lattice mismatch between MgO and GaAs. For the MgO layer prepared by sputtering, on the other hand, an amorphous MgO layer was initially grown on the GaAs substrate. Subsequently, a crystalline MgO layer was grown in the (001) direction. In the case of the EB-deposited MgO, as the MgO layer thickness increased, the degree of chemical order of the L1(0)-FePt layer increased from 55 to 81% owing to the improvement of the crystallinity of the MgO layer. The improvement of chemical order also led to the increase in the remanent magnetization of L1(0)-FePt from 84 to 98%. (C) 2012 The Japan Society of Applied Physics

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  66. Magnetic Anisotropy and Chemical Order of Artificially Synthesized L1(0)-Ordered FeNi Films on Au-Cu-Ni Buffer Layers Reviewed

    Takayuki Kojima, Masaki Mizuguchi, Tomoyuki Koganezawa, Keiichi Osaka, Masato Kotsugi, Koki Takanashi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 51 ( 1 )   2012.1

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    L1(0)-FeNi films were grown by alternate monatomic layer deposition on Au-Cu-Ni buffer layers at several substrate temperatures (T-s), and the relation between the uniaxial magnetic anisotropy energy (K-u) and the long-range chemical order parameter (S) was investigated. A large K-u of (7.0 +/- 0.2) x 10(6) erg/cm(3) and S of 0.48 +/- 0.05 were obtained. The value of K-u was larger than those reported previously for artificially synthesized FeNi films. It was first found that both K-u and S increased with T-s, and K-u was roughly proportional to S. (C) 2012 The Japan Society of Applied Physics

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  67. Ferromagnetic resonance study on FePt thin films with in-plane magnetization using coplanar waveguide Reviewed

    J. G. Kang, M. Mizuguchi, K. Takanashi

    MATERIALS INTEGRATION   Vol. 508   page: 261 - 265   2012

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    Ferromagnetic resonance (FMR) of epitaxial FePt thin films with in-plane magnetization was investigated by measuring the reflection coefficient (S-11) using coplanar waveguides. FMR signals of four FePt films grown on MgO (001) substrates with different post-annealing temperatures were measured, and the resonant peaks of FePt were successfully observed. Annealing temperature dependence was found in the peak frequency shift depending on the magnetic field applied in the film-plane, which is attributable to the difference of magnetic anisotropy of FePt thin films.

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  68. Magnetotransport properties of Co-C granular thin films depending on the carbon sputtering power Reviewed

    J. G. Kang, M. Mizuguchi, K. Takanashi

    Materials Research Society Symposium Proceedings   Vol. 1458   page: 1 - 6   2012

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    CoxC1-x granular films were deposited on Si substrates by a co-sputtering method. A large negative MR of 30.3% was obtained at 2 K for the sample prepared with the sputtering power of 50 W (C) and 4 W (Co). We have studied structural properties of Co-C granular films by Raman spectroscopy. Two peaks (D and G modes) from carbon bonds were clearly observed, and the intensity ratio of two peaks changed with the sputtering power, suggesting that the graphitization was promoted with the sputtering power. It was also revealed that the transport mechanism changed from tunneling to Mott's variable range hopping and MR decreased with the sputtering power. © 2012 Materials Research Society.

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  69. High-power rf oscillation induced in half-metallic Co2MnSi layer by spin-transfer torque Reviewed

    R. Okura, Y. Sakuraba, T. Seki, K. Izumi, M. Mizuguchi, K. Takanashi

    APPLIED PHYSICS LETTERS   Vol. 99 ( 5 )   2011.8

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    The rf oscillation induced in a current-perpendicular-to-plane device with Co2MnSi (CMS) layers by spin-transfer torque was investigated to enhance the rf output power due to the large magnetoresistance (MR) ratio. A large MR ratio of 12.5% was obtained due to the large spin-polarization of CMS, and fundamental and second harmonic rf oscillations were clearly observed in the CMS layer. A high rf output power of 1.1 nW was achieved in spite of a small precession angle of 8.6 degrees. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624470]

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  70. Co Content Effect on Magnetic Properties and Magnetoresistance of Co-C Nanocomposite Thin Films Reviewed

    Tang Ruihe, Wu Zhangben, Jiang He, Yang Zhigang, Zhang Chi, Mizuguchi Masaki, Takanashi Koki, Yang Bai, Yu Ronghai

    RARE METAL MATERIALS AND ENGINEERING   Vol. 40   page: 89 - 92   2011.6

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    Co-C nanocomposite thin films with Co content of 6.4 at%-16.4 at% were fabricated by magneton co-sputtering. TEM images show that the Co nanoparticles are dispersed uniformly in a carbon matrix, indicating typical granular characteristics. The average Co particle size is enlarged by increasing the Co content. Magnetic hysteresis loops reveal that, as Co content increases, magnetization of Co-C thin films is enhanced distinctly. The samples show high magnetization at low temperature and low magnetization at room temperature. Negative MR of 9.1%, 4.3% and 1.9% were observed for Co-C nanocomposite thin films with Co contents of 6.4 at%, 8.3 at% and 9.6 at%, respectively, at 4.2 K under an applied field of 90x79.6 kA.m(-1). The MR value is decreased with increasing Co content, which can be attributed to the evolution of microstructure.

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  71. Microstructure Affecting Magnetoresistance of a Cu-75-Fe-5-Ni-20 Alloy Reviewed

    Sung Kang, Mahoto Takeda, Dong-Sik Bae, Koki Takanashi, Masaki Mizuguchi

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 50 ( 4 )   2011.4

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    The electromagnetic properties of a Cu-75-Fe-5-Ni-20 alloy have been investigated upon isothermal annealing of the alloy at 873 K, using a superconducting quantum interference device (SQUID) magnetometer and a physical property measurement system (PPMS) instrument. Magnetoresistance (MR) was closely related to the magnetization value in specimens of the alloy. The most striking finding of the present work is that the as-quenched specimen with no visible precipitates attains the largest MR (similar to 16% at H = 7T and T = 10 K), although fine precipitates with a proper size were thought to be essential in our previous studies. The present investigation also revealed that several significant effects accompanied the magnetic and magnetoresistive properties, with microstructural evolution occurring during the phase decomposition of a Cu-75-Fe-5- Ni-20 alloy. (C) 2011 The Japan Society of Applied Physics

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  72. Ferromagnetic resonance of epitaxial Fe nanodots grown on MgO measured using coplanar waveguides Invited Reviewed

    M. Mizuguchi, K. Takanashi

    JOURNAL OF PHYSICS D-APPLIED PHYSICS   Vol. 44 ( 6 )   2011.2

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    Ferromagnetic resonance measurements of Fe nanodots epitaxially grown on a MgO layer were carried out using a coplanar waveguide to investigate the dynamic behaviours of spins in a magnetic dot assembly. The resonant peaks of Fe nanodots with an average diameter of 10 nm were successfully observed, and a strong magnetic anisotropy was found in the peak frequency shift depending on the magnetic field applied in the film plane. A difference was clearly seen in the peak shift behaviour between Fe nanodots and continuous Fe thin films. The Gilbert damping parameter of the Fe nanodots (nominal thickness: 3 nm) was estimated to be 0.008 12 from the width of the resonant peaks, substantially larger than that of a continuous Fe thin film with a thickness of 8 nm. This difference in damping is attributed to the distribution of the effective field in each nanodot due to size dispersion. Ferromagnetic resonance studies using coplanar waveguides thus enable clarification of the spin dynamics of magnetic dot arrays and the fundamental spin dynamics of a single nanodot.

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  73. Artificial Fabrication and Order Parameter Estimation of L10-ordered FeNi Thin Film Grown on a AuNi Buffer Layer Reviewed

    M. Mizuguchi, T. Kojima, M. Kotsugi, T. Koganezawa, K. Osaka, K. Takanashi

    Journal of the Magnetics Society of Japan     2011

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  74. Determination of local magnetic moment in L1(0)-FeNi using photoelectron emission microscopy (PEEM) Reviewed

    Masato Kotsugi, Masaki Mizuguchi, Shigeki Sekiya, Takuo Ohkouchi, Takayuki Kojima, Koki Takanashi, Yoshio Watanabe

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010)   Vol. 266   2011

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    Magnetic domain structure of L1(0)-type FeNi is observed by angular dependent photoelectron emission microscopy. It reveals the perpendicular magnetic component in magnetic domain structure with Bloch wall. The formation of Bloch wall is ascribed to the large magnetic anisotropy energy of L1(0)-FeNi.

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  75. L1(0)-ordered FeNi film grown on Cu-Ni binary buffer layer Reviewed

    T. Kojima, M. Mizuguchi, K. Takanashi

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010)   Vol. 266   2011

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    An FeNi film with a metastable L1(0)-ordered phase was fabricated by an alternate monatomic layer deposition. An Fe monolayer and a Ni monolayer were alternately grown on a Cu0.6Ni0.4 binary buffer layer. A (001) L1(0)-FeNi superlattice peak, which indicates the formation of a L1(0) phase, was clearly observed by an X-ray diffraction. A long-range order parameter S of L1(0)-FeNi was estimated to be 0.5 +/- 0.1. It was found that the film has a uniaxial magnetic anisotropy along c-axis by magnetization measurement. The uniaxial magnetic anisotropy energy K-u was evaluated to be (5.0 +/- 0.1) x 10(6) erg/cc.

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  76. Surface morphology and transport properties of Cr nanoparticles in single electron tunneling regime Reviewed

    Tetsunori Koda, Seiji Mitani, Masaki Mizuguchi, Koki Takanashi

    2ND INTERNATIONAL SYMPOSIUM ON ADVANCED MAGNETIC MATERIALS AND APPLICATIONS (ISAMMA 2010)   Vol. 266   2011

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    We have carried out an investigation of surface structures of Cr nanoparticles grown on a MgO layer for studying single electron tunneling (SET). Reflection high-energy electron diffraction pattern changes from spotty to streak with decreasing Cr nominal thickness, while Cr forms nano size particles with the size of around 3.5 nm in diameter for all the samples. The double tunnel junctions for the Cr nominal thickness of 0.1 nm show clear Coulomb blockade with the threshold voltage of 50 mV, indicating that this Cr nanoparticle satisfies the condition for the appearance of SET. The relatively large volume of the Cr nanoparticles may be related with the fact that tunnel magnetoresistance due to spin accumulation in Cr nanoparticles is small.

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  77. Spin Accumulation in Cr Nanoparticles in Single Electron Tunneling Regime Reviewed

    Tetsunori Koda, Seiji Mitani, Masaki Mizuguchi, Koki Takanashi

    IEEE TRANSACTIONS ON MAGNETICS   Vol. 46 ( 6 ) page: 2060 - 2062   2010.6

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    We have studied spin-dependent single electron tunneling in Cr nanoparticles with a diameter of 4 nm using Fe/MgO/Cr-nanoparticles/MgO/Fe double tunnel junctions. The transport properties are governed by the Coulomb blockade, showing suppression of current at low bias voltages. Magnetoresistance is clearly observed at a bias voltage over 0.25 V, and the magnetoresistance ratio increases with increasing bias voltage. These results suggest that the magnetoresistance is due to the spin accumulation in Cr nanoparticles. With some assumption, the minimum value of spin relaxation time in Cr nanoparticles is roughly estimated to be on the order of tens of nanoseconds.

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  78. Strong Temperature Dependence of Magnetoresistance in Co-C Granular Thin Films Reviewed

    Ruihe Tang, Masaki Mizuguchi, Hai Wang, Ronghai Yu, Koki Takanashi

    IEEE TRANSACTIONS ON MAGNETICS   Vol. 46 ( 6 ) page: 2144 - 2147   2010.6

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    Co-C granular thin films with a Co content of 6.4 at.% were deposited at room temperature by co-sputtering. The magnetotransport properties of the thin films were investigated within 2-300 K under magnetic fields up to 90 kOe. A large negative magnetoresistance (MR) of 27.6% was successfully observed at 2 K. As temperature (T) increased, negative MR decreased drastically. Meanwhile, positive MR with an organic MR (OMAR)-like shape emerged in a low magnetic field region. Ordinary MR (OMR) appeared in a high magnetic field region and can be verified by MR proportional to H(2) fitting. When reached 10 K, MR became completely positive. The MR effect showed strong temperature dependence. The interesting phenomena may help us gain a new insight into the spin-dependent transport in ferromagnetic metal (FM)/amorphous-carbon (alpha-C) system.

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  79. Characterization of Cu buffer layers for growth of L1(0)-FeNi thin films Reviewed

    M. Mizuguchi, S. Sekiya, K. Takanashi

    JOURNAL OF APPLIED PHYSICS   Vol. 107 ( 9 )   2010.5

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    A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L1(0)-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L1(0)-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L1(0)-FeNi thin films. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3337649]

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  80. Transmission of electrical signals by spin-wave interconversion in a magnetic insulator Reviewed

    Y. Kajiwara, K. Harii, S. Takahashi, J. Ohe, K. Uchida, M. Mizuguchi, H. Umezawa, H. Kawai, K. Ando, K. Takanashi, S. Maekawa, E. Saitoh

    Nature   Vol. 464 ( 7286 ) page: 262 - 266   2010.3

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    The energy bandgap of an insulator is large enough to prevent electron excitation and electrical conduction. But in addition to charge, an electron also has spin, and the collective motion of spin can propagateand so transfer a signalin some insulators. This motion is called a spin wave and is usually excited using magnetic fields. Here we show that a spin wave in an insulator can be generated and detected using spin-Hall effects, which enable the direct conversion of an electric signal into a spin wave, and its subsequent transmission through (and recovery from) an insulator over macroscopic distances. First, we show evidence for the transfer of spin angular momentum between an insulator magnet Y 3 Fe 5 O 12 and a platinum film. This transfer allows direct conversion of an electric current in the platinum film to a spin wave in the Y 3 Fe 5 O 12 via spin-Hall effects4-11. Second, making use of the transfer in a Pt/Y 3 Fe 5 O 12 /Pt system, we demonstrate that an electric current in one metal film induces voltage in the other, far distant, metal film. Specifically, the applied electric current is converted into spin angular momentum owing to the spin-Hall effect in the first platinum film; the angular momentum is then carried by a spin wave in the insulating Y 3 Fe 5 O 12 layer; at the distant platinum film, the spin angular momentum of the spin wave is converted back to an electric voltage. This effect can be switched on and off using a magnetic field. Weak spin damping in Y 3 Fe 5 O 12 is responsible for its transparency for the transmission of spin angular momentum. This hybrid electrical transmission method potentially offers a means of innovative signal delivery in electrical circuits and devices. © 2010 Macmillan Publishers Limited. All rights reserved.

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  81. Growth and Characterization of Ultrathin Fe Films on Molecule-Adsorbed MgO Surfaces Reviewed

    Takayuki Kojima, Masaki Mizuguchi, Kohei Oka, Seiji Mitani, Koki Takanashi

    MATERIALS TRANSACTIONS   Vol. 50 ( 11 ) page: 2512 - 2514   2009.11

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    Effects of the molecule-adsorption on a MgO surface on the growth of ultra-thin Fe films were investigated. Surface observation by reflection high-energy electron diffraction and ultra-high vacuum atomic force microscopy showed that the adsorption of molecules on the MgO surface affected the morphology of Fe films grown on the MgO surface. It was revealed that the surface flatness of Fe films was improved by appropriate molecule-adsorption on the MgO surface. [doi: 10.2320/matertrans.M2009218]

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  82. Large voltage-induced magnetic anisotropy change in a few atomic layers of iron Reviewed

    T. Maruyama, Y. Shiota, T. Nozaki, K. Ohta, N. Toda, M. Mizuguchi, A. A. Tulapurkar, T. Shinjo, M. Shiraishi, S. Mizukami, Y. Ando, Y. Suzuki

    NATURE NANOTECHNOLOGY   Vol. 4 ( 3 ) page: 158 - 161   2009.3

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    In the field of spintronics, researchers have manipulated magnetization using spin-polarized currents(1-3). Another option is to use a voltage-induced symmetry change in a ferromagnetic material to cause changes in magnetization or in magnetic anisotropy(4-14). However, a significant improvement in efficiency is needed before this approach can be used in memory devices with ultralow power consumption. Here, we show that a relatively small electric field (less than 100 mV nm(-1)) can cause a large change (similar to 40%) in the magnetic anisotropy of a bcc Fe(001)/MgO(001) junction. The effect is tentatively attributed to the change in the relative occupation of 3d orbitals of Fe atoms adjacent to the MgO barrier. Simulations confirm that voltage-controlled magnetization switching in magnetic tunnel junctions is possible using the anisotropy change demonstrated here, which could be of use in the development of low-power logic devices and non-volatile memory cells.

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  83. Detection of current-driven magnetic domain wall deformation using anisotropic magnetoresistance effect Reviewed

    H. Maekawa, T. Nozaki, S. Kasai, M. Mizuguchi, M. Shiraishi, T. Ono, Y. Suzuki

    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE   Vol. 204 ( 12 ) page: 3987 - 3990   2007.12

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    We report on an electrical detection of current driven domain wall (DW) deformation induced by a current pulse injection in arc-shaped permalloy (Py) submicron wires. Current polarity and pulse length dependence were investigated under an assisting external magnetic field. Initial DW states prepared by an application of a large magnetic field were distributed to two distinct DW states. A current pulse application promoted transition between them. In addition, the third DW state was established only by an application of the short pulses (&lt; 50 ns). This result suggests the possibility of the high-speed control of the DW dynamics. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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  84. Tunnel magnetoresistance of C(60)-Co nanocomposites and spin-dependent transport in organic semiconductors Reviewed

    Shinji Miwa, Masashi Shiraishi, Shinichi Tanabe, Masaki Mizuguchi, Teruya Shinjo, Yoshishige Suzuki

    PHYSICAL REVIEW B   Vol. 76 ( 21 ) page: 214414-1 - 214414-7   2007.12

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    Magnetization, electrical conduction, and magnetoresistance (MR) of C(60)-Co nanocomposites, where Co nanoparticles are dispersed in C(60) molecules, have been investigated over a wide temperature range and Co volume fraction. The C(60)-Co nanocomposites exhibit MR when the Co volume fraction is controlled in such a way that the conduction mechanism is dominated by tunneling of carriers between Co nanoparticles in the C(60) matrix. The MR, which is attributed to spin-polarized tunneling through the C(60) molecules, shows strong temperature dependence. Our results indicate that some paramagnetic components contribute to the observed MR. The material-dependent bias-voltage dependence of the MR ratio suggests that these paramagnetic components originate from the interface between organics and ferromagnets. The present study advances the fundamental understanding of spin-dependent transport in organic semiconductors.

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  85. Large magnetoresistance in rubrene-Co nano-composites Reviewed

    Haruka Kusai, Shinji Miwa, Masaki Mizuguchi, Teruya Shinjo, Yoshishige Suzuki, Masashi Shiraishi

    CHEMICAL PHYSICS LETTERS   Vol. 448 ( 1-3 ) page: 106 - 110   2007.11

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    We demonstrate fabrication of rubrene-Co nano-composites, yielding an introduction of a spin degree of freedom in rubrene-based, electronics devices, and report on large magnetoresistance (MR) ratio of 78% at 4.2 K. It is elucidated that the observed MR effect is ascribed to the magnetization of the Co nano-particles, and this indicates spin-dependent transport via rubrene molecules is achieved. In addition, the MR effect can be observed even at room temperature. (c) 2007 Elsevier B.V. All rights reserved.

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  86. Dependence on annealing temperatures of tunneling spectra in high-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions Reviewed

    Rie Matsumoto, Shingo Nishiokaa, Masaki Mizuguchi, Masashi Shiraishi, Hiroki Maehara, Koji Tsunekawa, David D. Djayaprawira, Naoki Watanabe, Yuichi Otani, Taro Nagahama, Akio Fukushima, Hitoshi Kubota, Shinji Yuasa, Yoshishige Suzuki

    SOLID STATE COMMUNICATIONS   Vol. 143 ( 11-12 ) page: 574 - 578   2007.9

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    We investigated the annealing temperature dependence of differential tunneling conductance spectra (dI/dV as a function of V) in CoFeB/teXtUred MgO(001)/CoFeB magnetic tunnel junctions (MTJs) that exhibit the giant tunneling magnetoresistance (TMR) effect at room temperature. The spectra were strongly affected by annealing the MTJs. A reduction in dI/dV at around 300 mV was observed only in annealed MTJs in which the CoFeB electrodes were crystallized in a bcc(001) structure. Because the reduction in conductance was observed in both MTJs that have a 1.8-nm-thick MgO barrier and MTJs that have a 3.2-nm-thick MgO barrier, we concluded that Delta(5) and Delta(2') evanescent states, which rapidly decay in the MgO tunneling barrier, are not the cause of the reduction in conductance. We believe the cause of the reduction is either the electronic structure of the interfaces between MgO(001)/bcc CoFeB(001) after annealing or a particular feature of Delta(1) states in MgO(001) or bee CoFeB(001). () 2007 Published by Elsevier Ltd

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  87. Spin-dependent transport in nanocomposites of Alq(3) molecules and cobalt nanoparticles Reviewed

    Shinichi Tanabe, Shinji Miwa, Masaki Mizuguchi, Teruya Shinjo, Yoshishige Suzuki, Masashi Shiraishia

    APPLIED PHYSICS LETTERS   Vol. 91 ( 6 ) page: 063123-1 - 063123-3   2007.8

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    The authors have observed magnetoresistance (MR) ratios of 12% and 0.1% at 4.2 and 290 K, respectively, in a nanocomposite in which Co nanoparticles are embedded in the fine molecular structure of a tris(8-hydroxyquinoline) aluminum (Alq(3)) matrix. Structural analyses, magnetization measurements, and conduction properties of the device reveal that the MR effect is induced by spin-dependent transport in the Alq(3). (c) 2007 American Institute of Physics.

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  88. Substantial reduction in the depinning field of vortex domain walls triggered by spin-transfer induced resonance Reviewed

    T. Nozaki, H. Maekawa, M. Mizuguchi, M. Shiraishi, T. Shinjo, Y. Suzuki, H. Maehara, S. Kasai, T. Ono

    APPLIED PHYSICS LETTERS   Vol. 91 ( 8 ) page: 082502-1 - 082502-3   2007.8

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    An influence of spin-transfer-induced resonant excitation of a vortex magnetic domain wall on magnetization reversal process was investigated in Permalloy nanowires. Sizable reduction of the depinning field was observed under an application of radio frequency current when the frequency coincided with resonance of the vortex core. The resonant frequency was found to increase by shrinking the wire width. These results lead the authors to conclude that the spin-transfer-induced resonant excitation assists the depinning of the vortex domain walls. This provides an important insight for the realization of novel magnetic memory and logic devices based on current-driven domain wall manipulation.

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  89. In situ scanning tunneling microscopy observations of polycrystalline MgO(001) tunneling barriers grown on amorphous CoFeB electrode Reviewed

    M. Mizuguchi, Y. Suzuki, T. Nagahama, S. Yuasa

    APPLIED PHYSICS LETTERS   Vol. 91 ( 1 ) page: 012507-1 - 012507-3   2007.7

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    Topological surface analysis using in situ scanning tunneling microscopy was performed for highly oriented polycrystalline (textured) MgO(001) tunneling barrier layers grown on amorphous CoFeB electrode layers. The microscopy revealed a MgO surface structure in which nanosized grains were dispersed on clusters that originated from the CoFeB underlayer. In situ annealing reduced this surface roughness. Local tunneling spectroscopy measurements revealed the formation of a nearly perfect and uniform tunneling barrier in spite of grain boundaries in the textured MgO(001) layer, which is consistent with the fact that textured CoFeB/MgO/CoFeB and fully epitaxial MgO-based magnetic tunnel junctions exhibit comparable spin-dependent tunneling properties. (c) 2007 American Institute of Physics.

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  90. Differential conductance measurements of low-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions Reviewed

    S. Nishioka, Y. V. Hamada, R. Matsumoto, M. Mizuguchi, M. Shiraishi, A. Fukushima, H. Kubota, T. Nagahama, S. Yuasa, H. Maehara, Y. Nagamine, K. Tsunekawa, D. D. Djayaprawira, N. Watanabe, Y. Suzuki

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 310 ( 2 ) page: E649 - E651   2007.3

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    We measured differential conductance spectra of magnetic tunnel junctions (MTJs) with thin MgO barrier and low-resistance area product. The spectra of MTJs with MgO barrier thicker than 1.05 nm were essentially the same except for slight decrease of contributions from low-energy excitations, such as magnons. The spectra of MTJ with 1.01 nm MgO barrier were thoroughly different from the MTJs with thicker barrier. The result reveals that an MTJ with very thin MgO barrier thickness has different conduction characteristics from those with thicker MgO barriers. (C) 2006 Elsevier B.V. All rights reserved.

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  91. Surface morphology of epitaxial magnetic tunnel junctions Invited Reviewed

    M. Mizuguchi, Y. Suzuki, T. Nagahama, S. Yuasa

    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY   Vol. 7 ( 1 ) page: 255 - 258   2007.1

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    The surface morphology of epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions, which show the giant tunneling magnetoresistance effect, was investigated by in situ scanning tunneling microscopy. It was observed that an epitaxial MgO barrier layer forms flat surface structures. The surface was flatter with distinct steps and terraces after annealing, which would lead to an increase of the tunneling magnetoresistance ratio. Examination of the local electronic structures of 1.05-nm-thick MgO barrier layers by scanning tunneling spectroscopy revealed no pinholes in the layers, so they would be perfect barriers in magnetic tunnel junctions.

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  92. コプレーナウェーブガイドを用いた強磁性共鳴の高感度測定 Reviewed

    戸田順之, 斉藤和広, 太田健太, 前川裕昭, 水口将輝, 白石誠司, 鈴木義茂

    日本応用磁気学会誌   Vol. 31   page: 435 - 438   2007

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  93. Spin-dependent transport in C-60-Co nano-composites Reviewed

    Shinji Miwa, Masashi Shiraishi, Masaki Mizuguchi, Teruya Shinjo, Yoshishige Suzuki

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   Vol. 45 ( 24-28 ) page: L717 - L719   2006.7

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    C-60-Co nano-composites, in which Co nano-particles are embedded in C-60 molecules, have been fabricated and a magnetoresistance (MR) ratio of 8% has been observed at T = 4.2 K. In addition, we have succeeded in observing a clear MR curve even at room temperature (RT). The MR effect is ascribed to magnetization of the Co nano-particles and spin-dependent transport in C-60 molecules. This study directly indicates that RT operation of molecular spin devices can be realized.

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  94. Microscopic structures of MgO barrier layers in single-crystal Fe/MgO/Fe magnetic tunnel junctions showing giant tunneling magnetoresistance Reviewed

    M. Mizuguchi, Y. Suzuki, T. Nagahama, S. Yuasa

    APPLIED PHYSICS LETTERS   Vol. 88 ( 25 ) page: 251901ー1 - 251901ー3   2006.6

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    The microscopic structures of MgO(001) barrier layers in magnetic tunnel junctions showing giant tunneling magnetoresistance were characterized by in situ scanning tunneling microscopy. The MgO thin films formed exceedingly flat surfaces, and their terraces were made even flatter by annealing after deposition. This flattening of MgO surfaces apparently promotes coherent transport of electrons, which should enhance the tunneling magnetoresistance ratio. Local tunneling spectroscopy revealed that an annealed MgO layer has a critical thickness between 3 and 5 ML (monolayer), and a continuous film without pinholes can be formed over the thickness. (c) 2006 American Institute of Physics.

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  95. 金属スピントロニクス素子の新しい展開ースピントルクダイオードー Reviewed

    鈴木義茂, Tulapurlar Ashwin, 水口将輝, 久保田均, 福島章雄, 湯浅新治, 前原大樹, 恒川孝二, ダビッド・ジャヤプラウィラ, 渡辺直樹

    キャノンアネルバ技報   Vol. Vol.12,   page: 5 - 10   2006.5

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  96. Fluorescence EXAFS analysis of local structures around Cr atoms in (Ga,Cr)As Reviewed

    H Ofuchi, M Yamada, J Okabayashi, M Mizuguchi, K Ono, Y Takeda, M Oshima, H Akinaga

    PHYSICA B-CONDENSED MATTER   Vol. 376   page: 651 - 653   2006.4

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    In this work, geometric structures for diluted magnetic semiconductor (Ga,Cr)As films grown by low-temperature molecular beam epitaxy were investigated by fluorescence extended X-ray absorption fine structure (EXAFS) measurements. The XAFS analysis has revealed that the majority of Cr atoms in the (Ga,Cr)As film substitute the Ga atoms in the GaAs lattice up to the Cr content x = 0.145. The abrupt change of the Cr-As bond lengths was observed between Cr content x = 0.06 and 0.145, which is due to inhomogeneous distribution of Cr atoms in GaAs matrix. It is expected that the paramagnetic behavior at room temperature in the samples above x = 0.145 is due to the inhomogeneous distribution of the Cr atoms doped in the GaAs matrix. (c) 2006 Elsevier B.V. All rights reserved.

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  97. Scanning tunneling microscopy observations of single-crystal Fe/MgO/Fe magnetic tunnel junctions Reviewed

    M Mizuguchi, Y Suzuki, T Nagahama, S Yuasa

    JOURNAL OF APPLIED PHYSICS   Vol. 99 ( 8 ) page: 08T308ー1 - 08T308ー3   2006.4

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    Scanning tunneling microscopy observations of a single-crystal Fe(001)/MgO(001)/Fe(001) magnetic tunnel junction which shows a large tunnel magnetoresistance effect were performed. Step-and-terrace structures of an epitaxial MgO barrier layer, which are very similar to surfaces of a bottom Fe underlayer, were observed. This indicates that the MgO terraces were grown flatly on each terrace of the Fe electrode. It is supposed that these atomically flat terraces enable a coherent tunneling of electrons through magnetic tunnel junctions. (C) 2006 American Institute of Physics.

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  98. Tunneling spectroscopy of magnetic tunnel junctions: Comparison between CoFeB/MgO/CoFeB and CoFeB/Al-O/CoFeB Reviewed

    M Mizuguchi, Y Hamada, R Matsumoto, S Nishioka, H Maehara, K Tsunekawa, DD Djayaprawira, N Watanabe, T Nagahama, A Fukushima, H Kubota, S Yuasa, M Shiraishi, Y Suzuki

    JOURNAL OF APPLIED PHYSICS   Vol. 99 ( 8 ) page: 08T309ー1 - 08T309ー3   2006.4

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    Tunneling spectroscopy measurements of magnetic tunneling junctions including two different barrier layers were performed. Intense dips at bias voltages of +/- 0.3 V were observed in second derivative conductance spectra only for a magnetic tunneling junction with a MgO barrier. It was concluded that the electronic structure of the MgO barrier has significant influence on the tunneling process of electrons through magnetic tunnel junctions. (C) 2006 American Institute of Physics.

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  99. スピン注入磁化反転素子の高周波特性 Reviewed

    鈴木義茂, A. Tulapurlar, 水口将輝, 久保田均, 福島章雄, 湯浅新治, 前原大樹, 恒川孝二, D. Djayaprawira, 渡辺直樹

    応磁研究会   Vol. 145回研究会   page: 49 - 55   2006.1

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  100. Tunneling spectra of sputter-deposited CoFeB/MgO/CoFeB magnetic tunnel junctions showing giant tunneling magnetoresistance effect Reviewed

    R Matsumoto, Y Hamada, M Mizuguchi, M Shiraishi, H Maehara, K Tsunekawa, DD Djayaprawira, N Watanabe, Y Kurosaki, T Nagahama, A Fukushima, H Kubota, S Yuasa, Y Suzuki

    SOLID STATE COMMUNICATIONS   Vol. 136 ( 11-12 ) page: 611 - 615   2005.12

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    We measured differential tunneling conductance (dI/dV, d(2)I/dV(2)) spectra of spin-valve-type magnetic tunnel junctions (MTJs) with a MgO(001) tunnel barrier layer and amorphous CoFeB ferromagnetic electrodes that show 315% magnetoresistance (MR) ratio at 4.3 K. The dI/dV spectra showed clear reduction in the conductance at around +/- 400 mV for a parallel magnetic configuration. Such anomalous spectra have never been observed for MTJs with an amorphous Al-O barrier. The d(2)I/dV(2) spectra showed several distinct peaks between 5 and 100 mv. Magnon excitations are assigned to an origin of those peaks and thought to be a dominant process to reduce MR at finite bias voltage. (c) 2005 Elsevier Ltd. All rights reserved.

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  101. Atomically flat aluminum-oxide barrier layers constituting magnetic tunnel junctions observed by in situ scanning tunneling microscopy Reviewed

    M Mizuguchi, Y Suzuki, T Nagahama, S Yuasa

    APPLIED PHYSICS LETTERS   Vol. 87 ( 17 ) page: 171909ー1 - 171909ー3   2005.10

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    Observation using in situ scanning tunneling microscopy of the layers constituting a magnetic tunnel junction with a naturally oxidized aluminum barrier layer revealed an extremely flat aluminum-oxide surface. It was clarified from line-scan images that the aluminum-oxide barrier layer has atomic steps. This flatness, which is surprising given that the aluminum-oxide film is amorphous, reduced electron scattering within the barrier, leading to momentum-dependent tunneling, which should enable the fabrication of advanced devices, such as spin-polarized resonant tunneling transistors. (C) 2005 American Institute of Physics.

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  102. Fluorescence EXAFS analysis of nanoscale zinc-blende MnAs dots grown on GaAs(001) by molecular beam epitaxy Reviewed

    H. Ofuchi, J. Okabayashi, M. Mizuguchi, M. Yamada, K. Ono, Y. Takeda, M. Oshima, H. Akinaga

    PHYSICA SCRIPTA   Vol. T115   page: 431 - 432   2005

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    In this work, geometric structures for ferromagnetic nanoscale zinc-blende MnAs dots grown on a sulfur-passivated GaAs(001) were investigated by using fluorescence EXAFS measurement. EXAFS measurements revealed that MnAs dots grown on GaAs(001) substrate did not form NiAs-type structure but zinc-blende structure. The Mn-As bond length in the MnAs dots is about 2.48 angstrom, which is close to that which was estimated from lattice constant of zinc-blende MnAs obtained by density-functional calculations. Existence of zinc-blende MnS (beta-MnS) phase was also observed by EXAFS measurements.

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  103. Magnetoresistive switch effect and its application to magnetic field sensors Reviewed

    ZG Sun, M Mizuguchi, H Akinaga

    PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5   Vol. 475-479   page: 2223 - 2226   2005

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    Magnetoresistive switch effect (MRS effect) devices containing two gold (Au) electrodes with a gap less than 2 gm were successfully fabricated on semi-insulting GaAs substrates by wet etching method. Huge MRS effect was observed. Magnetoresistance (MR) ratio reached 1,000,000% under the magnetic filed of 1.5 T when the devices were operated just above the threshold voltage. The magnetic field sensitivity at small magnetic fields was significantly improved. MR ratio of more than 1000% was achieved at 0.03 T. A relative high MR ratio of 100,000% under the magnetic filed of 1.5 T was also achieved when the devices operating before the threshold voltage.

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  104. Magnetoresistive switch effect and its application to magnetic field sensors

    Sun ZG, Mizuguchi M, Akinaga H

    PRICM 5: THE FIFTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-5   Vol. 475-479   page: 2223 - 2226   2005

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  105. Fluorescence EXAFS analysis of nanoscale zinc-blende MnAs dots grown on GaAs(001) by molecular beam epitaxy

    Ofuchi H., Okabayashi J., Mizuguchi M., Yamada M., Ono K., Takeda Y., Oshima M., Akinaga H.

    PHYSICA SCRIPTA   Vol. T115   page: 431 - 432   2005

  106. Fluorescence EXAFS analysis of nanoscale zinc-blende MnAs dots grown on GaAs(001) by molecular beam epitaxy Reviewed

    H. Ofuchi, J. Okabayashi, M. Mizuguchi, M. Yamada, K. Ono, Y. Takeda, M. Oshima, H. Akinaga

    Physica Scripta T   Vol. T115   page: 431 - 432   2005

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    In this work, geometric structures for ferromagnetic nanoscale zinc-blende MnAs dots grown on a sulfur-passivated GaAs(001) were investigated by using fluorescence EXAFS measurement. EXAFS measurements revealed that MnAs dots grown on GaAs(001) substrate did not form NiAs-type structure but zinc-blende structure. The MnAs bond length in the MnAs dots is about 2.48 Å which is close to that which was estimated from lattice constant of zinc-blende MnAs obtained by density-functional calculations. Existence of zinc-blende MnS (β-MnS) phase was also observed by EXAFS measurements. © Physica Scripta 2005.

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  107. Density-dependent electronic structure of zinc-blende-type MnAs dots on GaAs(001) studied by in situ photoemission spectroscopy Reviewed

    J Okabayashi, M Mizuguchi, K Ono, M Oshima, A Fujimori, H Kuramochi, H Akinaga

    PHYSICAL REVIEW B   Vol. 70 ( 23 ) page: 233305ー1 - 233305ー4   2004.12

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    We report on the density dependence of the morphology and electronic structure of zinc-blende-type MnAs dots using in situ photoemission spectroscopy combined with molecular-beam epitaxy. Transmission electron microscopy images showed the zinc-blende-type crystalline structure of 10-nm diameter for each dot on sulfur-passivated GaAs(001) surface. The valence-band photoemission spectra of the MnAs dots were similar to those of the diluted magnetic semiconductor Ga1-xMnxAs. With increasing dot density, the characteristic spectra of the zinc-blende-type MnAs persist but a weak Fermi edge appears, suggesting a metallic behavior as a result of percolation between the dots or the appearance of hexagonal MnAs as a minority phase.

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  108. Magnetic-field-controllable avalanche breakdown and giant magnetoresistive effects in Gold semi-insulating-GaAs Schottky diode Reviewed

    ZG Sun, M Mizuguchi, T Manago, H Akinaga

    APPLIED PHYSICS LETTERS   Vol. 85 ( 23 ) page: 5643 - 5645   2004.12

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    Gold (Au)/semi-insulating (SI)-GaAs Schottky diode was fabricated by the standard photolithography method using wet etching. Magnetic-field-dependent avalanche breakdown phenomena were observed in the current-voltage curves measured under magnetic field. The avalanche breakdown due to impact ionization was postponed to higher electrical field under applied magnetic field. Accordingly, threshold voltages of avalanche breakdown increased with the applied magnetic field. Above 0.2 T, avalanche breakdown was totally quenched. When Au-SI-GaAs Schottky diode was operated above the threshold voltage, giant mangetoresistive effects up to 100 000% were achieved under magnetic field of 0.8 T. (C) 2004 American Institute of Physics.

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  109. Zinc-blende CrAs/GaAs multilayers grown by molecular-beam epitaxy Reviewed

    H Akinaga, M Mizuguchi

    JOURNAL OF PHYSICS-CONDENSED MATTER   Vol. 16 ( 48 ) page: S5549 - S5553   2004.12

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    The epitaxial growth of zinc-blende CrAs/GaAs multilayers has been achieved by using the molecular-beam epitaxy method. The crystallographic quality was evaluated by reflection high-energy electron diffraction (RHEED) and cross-sectional transmission electron microscopy (TEM). The increase of the substrate temperature during growth up to 300degreesC brings the RHEED pattern to a streak, in contrast to the case at 200degreesC. TEM images show the atomically flat surface and interface of the multilayer.

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  110. Nano-oxide fabrication on thin-films of 3d-metal compounds and alloys Reviewed

    H Kuramochi, T Tokizaki, T Onuki, J Okabayashi, M Mizuguchi, F Takano, H Oshima, T Manago, H Akinaga, H Yokoyama

    SURFACE SCIENCE   Vol. 566   page: 349 - 355   2004.9

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    Nanometer-scale structures were fabricated by anodic oxidation using scanning probe microscopes on thin-films of various 3d-metal compounds and alloys on GaAs, such as MnAs, MnSb, Cr2O3, CoCr and NiFe. Material variation advances the developments in nano-fabrication by scanning probe microscope. Comparing the oxidation conditions, new methodology for fabrication of nano-devices is explored. (C) 2004 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.susc.2004.05.067

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  111. Dynamic magnetic properties of epitaxial MnAs thin films studied by spin-wave Brillouin scattering Reviewed

    A Murayama, K Hyomi, M Sakuma, Y Oka, J Okabayashi, M Mizuguchi, H Kuramochi, H Akinaga

    JOURNAL OF APPLIED PHYSICS   Vol. 95 ( 11 ) page: 6619 - 6621   2004.6

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    Dynamic magnetic properties of epitaxial MnAs thin films are studied by means of Brillouin light scattering (BLS). The sharp spectral peaks of the inelastic BLS are observed in room temperature, which are attributed to surface spin waves indicating the long-wavelength collective behavior of ferromagnetic spins. The field dependence of the surface spin-wave frequency is strongly affected by an in-plane angle between the crystal axis and the external field direction in a GaAs(100)/MnAs(-1100) film, which originates from uniaxial magnetic anisotropy parallel to the MnAs[11-20] axis and the modified g value. Significant damping of the spin-wave BLS spectrum is observed with increasing excitation laser power, possibly due to thermal effects. (C) 2004 American Institute of Physics.

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  112. Density dependence of zinc-blende MnAs dots studied by X-ray absorption spectroscopy and X-ray magnetic circular dichroism Reviewed

    J. Okabayashi, M. Mizuguchi, K. Ono, M. Oshima, A. Fujimori, M. Yuri, C. T. Chen, H. Akinaga

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 272   page: E1553 - E1555   2004.5

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    Zinc-blende type nanoscale MnAs dots were grown on a sulfur-passivated GaAs (0 0 1) surface by molecular beam epitaxy. We report on the dot density dependence of the X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) in the Mn 2p core-level region. The XAS spectrum of low-density MnAs dots showed "localized'' behavior as in the case of (Ga, Mn) As, while the spectrum of high-density MnAs dots changed to metallic behavior. The magnetic-field dependence of the XMCD revealed ferromagnetic behavior in the case of high-density MnAs dots. (C) 2003 Elsevier B. V. All rights reserved.

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  113. Magnetic properties and domain structures of FeSiB thin films Reviewed

    ZG Sun, H Kuramochi, M Mizuguchi, F Takano, Y Semba, H Akinaga

    SURFACE SCIENCE   Vol. 556 ( 1 ) page: 33 - 38   2004.5

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    Smooth Fe78Si10B12 thin films were prepared by r.f. sputtering with the very slow deposition rate of 0.59 nm/min. The as-deposited films were not fully amorphous, instead alpha-Fe(Si) nanocrystallites were found to be embedded in the amorphous matrix. The saturation magnetostriction lambda(s) of the as-deposited film is about 6.5 x 10(-6). After annealing at 540 degreesC for 1 h in an ultrahigh vacuum (4.5 x 10(-5) Pa), the fraction of alpha-Fe(Si) crystalline phase largely increased, and correspondingly the lambda(s) decreased to 4.5 x 10(-7). Ripple domain structures were observed in the as-deposited film, while dense stripe domains were observed in the annealed sample, characterized by a very narrow domain width of 80 nm. (110) texture and island-like configuration of alpha-Fe(Si) nanocrystallites formed by the annealing treatment are responsible for the perpendicular anisotropy. For the as-deposited film, the magnetization curves increased linearly with the increase of the magnetic field, and showed the very small hysteresis. On the other hand, the annealed sample clearly showed a very steep jump near the origin, which is due to the switch process of the dense stripe domain. (C) 2004 Elsevier B.V. All rights reserved.

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  114. Magnetic properties and domain structures of FeSiB thin films prepared by RF-sputtering method Reviewed

    ZG Sun, H Kuramochi, M Mizuguchi, F Takano, Y Semba, H Akinaga

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 272   page: 1160 - 1161   2004.5

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    Smooth Fe78Si10B12 thin films were prepared by RF sputtering with a very slow deposition rate of 0.59nm/min. The as-deposited films are not fully amorphous, instead alpha-Fe(Si) nanocrystallites are found to embed in the amorphous matrix. Ripple domain structures are observed in the as-deposited film. After annealing at 540degreesC for 1 h in an ultrahigh vacuum (4.5 x 10(-5) Pa), dense stripe domains are observed, characterized by a very narrow domain width of 80 nm. (110) texture and island-like configuration of alpha-Fe(Si) nanocrystallites during annealing treatment are responsible for the perpendicular anisotropy. (C) 2004 Elsevier B.V. All rights reserved.

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  115. Room temperature magnetoresistance effect observed in Au/GaAs films processed by focused ion beam Reviewed

    Masaki Mizuguchi, Takashi Manago, Hiro Akinaga

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 272   page: E1385 - E1386   2004.5

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    Huge magnetoresistance (MR) effect was observed in Au/GaAs films with a nano-size trench fabricated by a focused ion beam process. Positive MR effect with the ratio of 32,000% was obtained in the magnetic field of 15,000 Oe at room temperature. This huge MR effect is promising for the application to spintronic devices such as magnetic sensors. (C) 2003 Elsevier B.V. All rights reserved.

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  116. Au/GaAs magnetoresistive-switch-effect devices fabricated by wet etching Reviewed

    ZG Sun, M Mizuguchi, H Akinaga

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   Vol. 43 ( 4B ) page: 2101 - 2103   2004.4

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    Au/GaAs magnetoresistive-switch-effect (MRS effect) devices were successfully fabricated by the wet etching method. A large MRS effect was observed. In the current-voltage curves, the current jumped steeply at a threshold voltage of 32.0 V. The threshold voltages shifted to higher values and became less steep with increasing magnetic field. Above 2,000 Oe, no current jump driven by the applied voltage could be observed. The magnetoresistance (MR) ratio reached 1,000,000% at 15,000 Oe when the devices were operated above the threshold voltage. Also magnetic field sensitivity was greatly improved. To achieve a 1000% MR ratio, only 300 Oe was required at 32.2 V.

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  117. X-ray absorption spectroscopy of transition-metal doped diluted magnetic semiconductors Zn(1-)x(M)xO Reviewed

    J Okabayashi, K Ono, M Mizuguchi, M Oshima, SS Gupta, DD Sarma, T Mizokawa, A Fujimori, M Yuri, CT Chen, T Fukumura, M Kawasaki, H Koinuma

    JOURNAL OF APPLIED PHYSICS   Vol. 95 ( 7 ) page: 3573 - 3575   2004.4

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    We have investigated the electronic structure of Zn1-xMxO (M: 3d transition metal) by x-ray absorption spectroscopy. Using configuration-interaction cluster-model analyses, electronic structure parameters have been deduced and their chemical trend is discussed. Results show that the p-d exchange constant Nbeta is negative and large in cases of Mn, Fe, and Co, which is consistent with the enhancement of magnetic circular dichroism. (C) 2004 American Institute of Physics.

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  118. Magnetic pole pinning at rectangular defects on MnAs/GaAs(001) Reviewed

    H Kuramochi, J Okabayashi, F Takano, M Mizuguchi, T Manago, H Akinaga

    SURFACE SCIENCE   Vol. 550 ( 1-3 ) page: 192 - 198   2004.2

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    Strong magnetic poles at characteristic rectangular defects have been observed using a magnetic force microscope on a MnAs((1) over bar 1 0 0) thin film with the thickness of 30 nm. The MnAs thin film was epitaxially grown on a GaAs(0 0 1) substrate. The magnetic poles were in one-arranging direction, being independent of the magnetization direction of the film. The poles were pinned at the edges of the rectangular defects until just below the Curie temperature, and formed a stable magnetic-field loop on the MnAs surface. The stability of the magnetic pole pinning shows the distinctive feature of the magnetic domain structure on the surface with a strong anisotropy, which was built in the heterostructure of MnAs and GaAs. (C) 2003 Elsevier B.V. All rights reserved.

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  119. Electronic and magnetic properties of MnAs nanoclusters studied by x-ray absorption spectroscopy and x-ray magnetic circular dichroism Reviewed

    J Okabayashi, M Mizuguchi, M Oshima, H Shimizu, M Tanaka, M Yuri, CT Chen

    APPLIED PHYSICS LETTERS   Vol. 83 ( 26 ) page: 5485 - 5487   2003.12

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    We have investigated the electronic and magnetic properties of a MnAs:GaAs granular film with MnAs clusters embedded in the GaAs matrix fabricated by high-temperature annealing of Ga1-xMnxAs using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The XAS line shapes in the Mn 2p core level changed from a localized structure to an itinerant NiAs-type one. Magnetic-field dependence of the XMCD revealed no hysteresis curves at the fixed photon energy where the large XMCD signals were observed, suggesting the superparamagnetic behavior at 100 K. (C) 2003 American Institute of Physics.

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  120. Magnetic domain structure of MnAs thin films as a function of temperature

    Mizuguchi M, Kuramochi H, Okabayashi J, Manago T, Akinaga H

    MATERIALS TRANSACTIONS   Vol. 44 ( 12 ) page: 2578 - 2581   2003.12

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  121. Magnetic domain structure of MnAs thin films as a function of temperature Reviewed

    M Mizuguchi, H Kuramochi, J Okabayashi, T Manago, H Akinaga

    MATERIALS TRANSACTIONS   Vol. 44 ( 12 ) page: 2578 - 2581   2003.12

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    We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a magnetic force microscope. We observed, by an atomic force microscope, rectangular defects along GaAs [110] direction which disperse randomly on the surface of MnAs/GaAs (001). The Curie temperature of MnAs is 45degreesC, and it is successfully confirmed directly by the variable temperature magnetic force microscope observation. We also investigated magnetic domain structures of MnAs/GaAs (111)B, and no apparent relation was observed between the topographic structure and the magnetic domain structure.

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  122. Fluorescence extended X-ray absorption fine structure analysis of half-metallic ferromagnet "zinc-blende CrAs" grown on GaAs by molecular beam epitaxy

    Ofuchi H, Mizuguchi M, Ono K, Oshima M, Akinaga H, Manago T

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS   Vol. 199   page: 227 - 230   2003.1

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  123. Fluorescence extended X-ray absorption fine structure analysis of half-metallic ferromagnet "zinc-blende CrAs" grown on GaAs by molecular beam epitaxy Reviewed

    H Ofuchi, M Mizuguchi, K Ono, M Oshima, H Akinaga, T Manago

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS   Vol. 199   page: 227 - 230   2003.1

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    In this work, geometric structures for a half-metallic ferromagnet "zinc-blende CrAs", which showed ferromagnetic behavior beyond room temperature, were investigated using fluorescence extended X-ray absorption fine structure (EXAFS) measurement. The EXAFS measurements revealed that As atoms around Cr atoms in the 2 nm CrAs film grown on a GaAs(O 0 1) substrate were coordinated tetrahedrally, indicating formation of zinc-blende CrAs. The Cr-As bond length in the zinc-blende CrAs is 2.49 Angstrom This value is close to that which was estimated from the lattice constant (5.82 Angstrom) of ferromagnetic zinc-blende CrAs calculated by full-potential linearized augmented-plane wave method. The EXAFS analysis show that the theoretically predicted zinc-blende CrAs can be fabricated on GaAs(O 0 1) substrate by low-temperature molecular-beam epitaxy. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0168-583X(02)01539-2

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  124. Formation, properties and photoelectron spectroscopy of magnetic nanostructures

    Oshima M, Mizuguchi M, Ono K, Akinaga H, Sugiyama M

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   Vol. 124 ( 2-3 ) page: 165 - 174   2002.7

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  125. Formation, properties and photoelectron spectroscopy of magnetic nanostructures Reviewed

    M Oshima, M Mizuguchi, K Ono, H Akinaga, M Sugiyama

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   Vol. 124 ( 2-3 ) page: 165 - 174   2002.7

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    In order to realize magnetic nanocrystals for spin electronic devices, we have successfully grown MnAs and/or MnSb nanocrystals on atomically controlled GaAs(001) substrates by molecular beam epitaxy. Surface structures of sulfur- and antimony-terminated GaAs substrates are characterized by synchrotron radiation soft X-ray standing waves. Then, Mn pnictide nanocrystals are grown by super Volmer-Weber epitaxy, taking advantage of low surface energy. MnAs and/or MnSb nanocrystals grown on sulfur-terminated GaAs(001) substrates show ferromagnetic properties with size of 20-30 nm and surface density of more than 10(10) cm(-2). Photoelectron spectroscopy revealed the electronic structures of these magnetic dots. (C) 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0368-2048(02)00052-X

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  126. In-situ photoelectron spectroscopy of magnetic dots and magnetic semiconductor nanostructures

    Oshima M, Ono K, Mizuguchi M, Yamada M, Okabayashi J, Fujimori A, Akinaga H, Shirai M

    INTERNATIONAL JOURNAL OF MODERN PHYSICS B   Vol. 16 ( 11-12 ) page: 1681 - 1690   2002.5

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  127. Epitaxial growth of zinc-blende CrAs/GaAs multilayer Reviewed

    M Mizuguchi, H Akinaga, T Manago, K Ono, M Oshima, M Shirai, M Yuri, HJ Lin, HH Hsieh, CT Chen

    JOURNAL OF APPLIED PHYSICS   Vol. 91 ( 10 ) page: 7917 - 7919   2002.5

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    Zinc-blende CrAs/GaAs multilayers were grown by molecular beam epitaxy. It was certified that each CrAs layer maintains an epitaxial relationship with the zinc-blende GaAs structure judging from the reflection high-energy electron diffraction observation. The film contains thicker zinc- blende CrAs layers in total than the CrAs thin film directly grown on the GaAs substrate which has the critical thickness of 3 nm. It was clarified that the optimum thicknesses of CrAs and GaAs to keep a good epitaxial relationship are 2 ML and 2 ML, respectively. The electronic structure of the multilayer is thought to be close to that of the (Ga, Cr)As thin film which has 50% of Cr content judging from x-ray absorption spectroscopy measurements. (C) 2002 American Institute of Physics.

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  128. Fabrication, magnetic properties, and electronic structures of nanoscale zinc-blende MnAs dots (invited) Reviewed

    K Ono, J Okabayashi, M Mizuguchi, M Oshima, A Fujimori, H Akinaga

    JOURNAL OF APPLIED PHYSICS   Vol. 91 ( 10 ) page: 8088 - 8092   2002.5

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    Ferromagnetic nanoscale zinc-blende MnAs dots were successfully fabricated on a sulfur-passivated GaAs (001) surface by molecular-beam epitaxy. Transmission electron microscopy and selected area electron diffraction showed that the crystalline structure was not the same as that of bulk MnAs with NiAs-type hexagonal crystalline structure, but of zinc-blende type. In in situ photoemission spectroscopy of the zinc-blende MnAs dots, the Fermi edge was not clearly observed and the Mn 3d partial density of states was similar to that of the diluted ferromagnetic semiconductor Ga1-xMnxAs, which also supports the fabrication of zinc-blende MnAs in the nanoscale. (C) 2002 American Institute of Physics.

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  129. In-situ photoelectron spectroscopy of magnetic dots and magnetic semiconductor nanostructures Reviewed

    M Oshima, K Ono, M Mizuguchi, M Yamada, J Okabayashi, A Fujimori, H Akinaga, M Shirai

    INTERNATIONAL JOURNAL OF MODERN PHYSICS B   Vol. 16 ( 11-12 ) page: 1681 - 1690   2002.5

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    High resolution angle-resolved photoelectron spectroscopy (ARPES) has been performed on magnetic nanostructures which were in-situ grown hetero-epitaxially on GaAs substrates by low temperature molecular beam epitaxy. Sulfur termination of GaAs surfaces enabled the formation of NiAs-type MnSb dots and zinc-blende (zb) type MnAs dots, showing huge magnetoresistance at RT and half-metallic behavior, respectively. ARPES analysis revealed that the zb-MnAs dots show unique valence band feature with Mn 3d-related peak at about 4 eV of binding energy which is quite similar to (Ga,Mn)As DMS Films. Zb-CrAs thin films on GaAs with T, higher than RT are found to show the band dispersion within 2 eV near the Fermi edge, which is in good agreement with the FLAPW calculation. We have also found that (Ga,Cr)As DMS thin films have the similar valence band features to zb-CrAs.

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  130. Growth of ferromagnetic semiconductor: (Ga,Cr)As Reviewed

    M Yamada, K Ono, M Mizuguchi, J Okabayashi, M Oshima, M Yuri, HJ Lin, HH Hsieh, CT Chen, H Akinaga

    JOURNAL OF APPLIED PHYSICS   Vol. 91 ( 10 ) page: 7908 - 7910   2002.5

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    A type of GaAs-based ferromagnetic semiconductor, (Ga, Cr)As, was successfully prepared by low-temperature molecular-beam epitaxy. The (Ga, Cr)As thin film shows a flat surface up to the Cr content x=0.18. However, when Cr content x exceeded 0.20, the roughness of the film became larger. The ferromagnetic ordering of the semiconductor sample with the Cr content of x=0.11 was observed. The electronic structures of (Ga, Cr)As were characterized by x-ray absorption spectroscopy (XAS). The XAS spectra show different line shapes in different Cr content. (C) 2002 American Institute of Physics.

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  131. Enchanced magnetooptical response of magnetic nanoclusters embedded in semiconductor

    Akinaga H, Mizuguchi M, Manago T, Gan'shina E, Granovsky A, Rodin I, Vinogradov A, Yurasov A

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 242   page: 470 - 472   2002.4

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  132. Enchanced magnetooptical response of magnetic nanoclusters embedded in semiconductor Reviewed

    H Akinaga, M Mizuguchi, T Manago, E Gan'shina, A Granovsky, Rodin, I, A Vinogradov, A Yurasov

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 242   page: 470 - 472   2002.4

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    In the present work, we report the results of an experimental study of magnetooptical Kerr effect and optical properties in MnAs:GaAs granular films in the spectral range 0.5-4.5 eV at room temperature and at 4.2 K. The possible mechanisms of the giant magnetooptical effect in MnAs:GaAs granular films are discussed on the basis of the obtained results. (C) 2002 Elsevier Science B.V. All rights reserved.

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  133. Growth of Fe(100) on GaAs(100) for tunnel magneto-resistance junctions

    Manago T, Mizuguchi M, Akinaga F

    JOURNAL OF CRYSTAL GROWTH   Vol. 237   page: 1378 - 1382   2002.4

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  134. Growth of Fe(100) on GaAs(100) for tunnel magneto-resistance junctions Reviewed

    T Manago, M Mizuguchi, F Akinaga

    JOURNAL OF CRYSTAL GROWTH   Vol. 237   page: 1378 - 1382   2002.4

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    We prepared epitaxially grown Fe films on GaAs (0 0 1) surfaces with different reconstructions. The Ga and As concentrations as a function of the Fe thickness were investigated by Auger electron spectroscopy (AES). The Ga atoms hardly segregated, while the AES signal of As still remained at 20 run under a low deposition rate (0.02 nm/s). The segregation was considerably suppressed by the higher deposition rate (0.08 nm/s). The cross-scetional transmission electron microscopy (TEM) image showed that an interface between GaAs and Fe was atomically flat and the surface of the 20 nm Fe film was very flat. We have succeeded in preparing Co/Al2O3/Fe(0 0 1) tunnel junctions based on an Fe(0 0 1) film. The MR ratio was about 9-11 %. (C) 2002 Elsevier Science B.V. All rights reserved.

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  135. Band discontinuity in the GaAs/AlAs interface studied by in situ photoemission spectroscopy Reviewed

    J Okabayashi, K Ono, T Mano, M Mizuguchi, K Horiba, K Nakamura, A Fujimori, M Oshima

    APPLIED PHYSICS LETTERS   Vol. 80 ( 10 ) page: 1764 - 1766   2002.3

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    In order to investigate the valence-band discontinuity of the GaAs/AlAs interface, the thickness dependence of the photoemission spectra of a GaAs layer in situ deposited on AlAs by molecular-beam epitaxy has been studied. Although the interface is atomically abrupt, the electronic structure in the interface region displays Al1-xGaxAs alloy-like behaviors. The valence-band maximum as well as the Ga 3d core level show a gradual shift as a function of GaAs layer thickness of less than 2 nm (8 monolayers), which indicates that interface formation needs about 2 nm thickness for the electronic structure of the GaAs layer to become that of bulk GaAs. (C) 2002 American Institute of Physics.

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  136. Epitaxial growth of new half-metallic ferromagnet "zinc-blende CrAs" and the substrate temperature dependence

    Mizuguchi M, Akinaga H, Manago T, Ono K, Oshima M, Shirai M

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 239 ( 1-3 ) page: 269 - 271   2002.2

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  137. Epitaxial growth of new half-metallic ferromagnet "zinc-blende CrAs" and the substrate temperature dependence Reviewed

    M Mizuguchi, H Akinaga, T Manago, K Ono, M Oshima, M Shirai

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 239 ( 1-3 ) page: 269 - 271   2002.2

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    Epitaxial zinc-blende CrAs thin films were grown at two different temperatures. CrAs (2 nm) grown at 200degreesC formed plateau-shapes, whereas CrAs (2 mn) grown at 300degreesC formed dispersed dots. The thin film grown at 200degreesC showed ferromagnetic behavior at room temperature, and the Curie temperature was estimated to be over 400 K. (C) 2002 Elsevier Science B.V. All rights reserved.

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  138. Thickness dependence of photoemission spectra in zinc-blende CrAs

    Mizuguchi M, Ono K, Oshima M, Okabayashi J, Akinaga H, Manago T, Shirai M

    SURFACE REVIEW AND LETTERS   Vol. 9 ( 1 ) page: 331 - 334   2002.2

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  139. Thickness dependence of photoemission spectra in zinc-blende CrAs Reviewed

    M Mizuguchi, K Ono, M Oshima, J Okabayashi, H Akinaga, T Manago, M Shirai

    SURFACE REVIEW AND LETTERS   Vol. 9 ( 1 ) page: 331 - 334   2002.2

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    The electronic structure of CrAs thin films with nominal thicknesses of 2 nm and 30 nm were studied by angle-resolved photoemission spectroscopy using synchrotron radiation. The CrAs film of 2 nm is expected to form a zinc-blende phase which is predicted to have a half-metallic band structure by theoretical calculation. On the other hand, it is considered that the CrAs film of 30 nm is a polycrystalline compound judging from reflection high-energy electron diffraction patterns. Different valence-band photoemission spectra were obtained for the two films. The photoemission spectra of the CrAs film of 30 nm showed no band dispersion, whereas a band dispersion was observed in that of the CrAs film with the nominal thickness of 2 nm.

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  140. 完全スピン偏極強磁性体CrAsの物質設計および合成 Reviewed

    眞砂卓史, 水口将輝, 秋永広幸, 白井正文, 小野寛太, 尾嶋正治

    日本応用磁気学会誌   Vol. 26   page: 441 - 444   2002

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  141. Automated angle-scanning photoemission end-station with molecular beam epitaxy at KEK-PF BL-1C

    Ono K, Yeom HW, Horiba K, Oh JH, Nakazono S, Kihara T, Nakamura K, Mano T, Mizuguchi M, Oshima M, Aiura Y, Kakizaki A

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT   Vol. 467   page: 1497 - 1501   2001.7

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  142. Performance of the high-resolution high-flux monochromator for bending magnet beamline BL-1C at the Photon Factory

    Ono K, Oh JH, Horiba K, Mizuguchi M, Oshima M, Kiyokura T, Maeda F, Watanabe Y, Kakizaki A, Kikuchi T, Yagishita A, Kato H

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT   Vol. 467   page: 573 - 576   2001.7

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  143. Automated angle-scanning photoemission end-station with molecular beam epitaxy at KEK-PF BL-1C Reviewed

    K Ono, HW Yeom, K Horiba, JH Oh, S Nakazono, T Kihara, K Nakamura, T Mano, M Mizuguchi, M Oshima, Y Aiura, A Kakizaki

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT   Vol. 467   page: 1497 - 1501   2001.7

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    In order to satisfy demands to study the electronic structure of quantum nanostructures, a VUV beamline and a high-resolution and high-throughput photoemission end-station combined with a molecular beam epitaxy (MBE) system have been constructed at the BL-IC of the Photon Factory. An angle-resolved photoemission spectrometer, having high energy- and angular-resolutions; VG Microtech ARUPS10, was installed. The total energy resolution of 31 meV at the 60 eV of photon energy is achieved. For the automated angle-scanning photoemission, the electron spectrometer mounted on a two-axis goniometer can be rotated in vacuum by the computer-cont rolled stepping motors. Another distinctive feature of this end-station is a connection to a MBE chamber in ultahigh vacuum (UHV). In this system, MBE-grown samples can be transferred into the photoemission chamber without breaking UHV. Photoemission spectra of MBE-grown GaAs(001) surfaces were measured with high-resolution and bulk and surface components are clearly resolved. (C) 2001 Elsevier Science B.V, All rights reserved.

    DOI: 10.1016/S0168-9002(01)00734-3

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  144. Performance of the high-resolution high-flux monochromator for bending magnet beamline BL-1C at the Photon Factory Reviewed

    K Ono, JH Oh, K Horiba, M Mizuguchi, M Oshima, T Kiyokura, F Maeda, Y Watanabe, A Kakizaki, T Kikuchi, A Yagishita, H Kato

    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT   Vol. 467   page: 573 - 576   2001.7

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    A grazing incidence varied line spacing plane grating monochromator (VLS-PGM) has been designed and installed at the Photon Factory bending magnet beamline, BL-1C. The monochromator is designed to cover 20 to 250eV with a high resolving power as well as a high photon flux and intended for a high-resolution angle-resolved photoemission study of quantum nano-structures. The resolving power of the beamline is observed to be more than 16,000 at around 65 eV and exceeds 10,000 at all the covered energy ranges of the monochromator with photon flux over 10(9) photons/s which shows that this monochromator reaches the expected design goals. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0168-9002(01)00415-6

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  145. Magnetic properties of MnSb granular films

    Mizuguchi M, Akinaga H, Ono K, Oshima M

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 226   page: 1838 - 1839   2001.5

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  146. Magnetoresistive switch effect in MnSb granular films grown on sulfur-passivated GaAs: more-than 10 000% magnetoresistance effect at room-temperature Reviewed

    H Akinaga, M Mizuguchi, T Manago, T Sato, H Kuramochi, K Ono, H Ofuchi, M Oshima

    PHYSICA E   Vol. 10 ( 1-3 ) page: 447 - 451   2001.5

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    A huge positive magnetoresistance effect, more than 10 000% at room temperature, has been discovered in MnSb granular films. Granular films consisting of nanoscale MnSb dots were fabricated on a sulfur-passivated GaAs (001) substrate by molecular-beam epitaxy, then covered with an Sb thin layer. The MnSb granular films exhibit a strong in-plane anisotropy of the magnetic-field-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied in the [1 1 0] direction of the GaAs (0 0 1) surface, a steep change in the current, which we term magnetoresistive switch (MRS), is driven by the huge magnetoresistance effect under a relatively low magnetic field (less than about 0.2 T). On the other hand, less than 1% magnetoresistance effect was observed when the voltage was applied in thr [1 10] direction of the GaAs surface. The origin of the anisotropy is discussed in terms of the microscopic structural anisotropy at the heterointerface. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S1386-9477(01)00135-7

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  147. Magnetoresistive switch effect in MnSb granular films grown on sulfur-passivated GaAs: more-than 10 000% magnetoresistance effect at room-temperature

    Akinaga H, Mizuguchi M, Manago T, Sato T, Kuramochi H, Ono K, Ofuchi H, Oshima M

    PHYSICA E   Vol. 10 ( 1-3 ) page: 447 - 451   2001.5

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  148. Magnetic properties of MnSb granular films Reviewed

    M Mizuguchi, H Akinaga, K Ono, M Oshima

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   Vol. 226   page: 1838 - 1839   2001.5

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    Magnetoresistance (MR) effects were investigated on MnSb granular films. These films were composed of GaAs substrates, deposited MnSb dots, and Sb capping layers. With increasing nominal thickness of MnSb, a sudden increase in the magnetic circular dichroism intensity was observed over 0.7 nm. The extra-huge positive MR effect more than 10,000% was observed for the sample with the nominal thickness of 0.2 = at room temperature. I-V curve analysis showed the jump from the high-resistance state to the low-resistance state at the critical voltage. It is considered that the coalescence among dots which occurs at a certain nominal thickness plays an important role in the extra-huge MR effect. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0304-8853(00)00619-3

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  149. Properties of semiconductor quantum dots and magnetic nanocrystals grown by molecular beam epitaxy Reviewed

    M Oshima, T Mano, M Mizuguchi, K Ono, H Fujioka, H Akinaga, N Koguchi

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   Vol. 38 ( 4 ) page: 396 - 400   2001.4

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    In order to realize a combined system of semiconductor and magnetic nanocrystals fur advanced nanoelectronics, we tried tu heteroepitaxially grow both InGaAs quantum dots on GaAs(001) substrates for laser applications and MnAs and/or MnSb nanocrystals for high-density magnetic recording media by using molecular beam epitaxy. InGaAs and Mn pnictide clots were grown by using modified droplet epitaxy and super Volmer-Weber epitaxy, respectively, taking advantages of self-organization, solid-phase crystallization and low surface energy, respectively. The InGaAs quantum dots exhibited a very sharp PL emission at 946 nm with a full width at half maximum of 21.6 meV, suggesting a drastic improvement in dot size uniformity and crystalline quality over the conventional Stranski-Krastanov dots. On the other hand, the MnAs and/or MnSL nanocrystals grown on sulfur-passivated GaAs(001) substrates show ferromagnetic properties with a size of 16 nm and a surface density of about 10(11) cm(-2).

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  150. Properties of semiconductor quantum dots and magnetic nanocrystals grown by molecular beam epitaxy

    Oshima M, Mano T, Mizuguchi M, Ono K, Fujioka H, Akinaga H, Koguchi N

    JOURNAL OF THE KOREAN PHYSICAL SOCIETY   Vol. 38 ( 4 ) page: 396 - 400   2001.4

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  151. MnSb:GaAsグラニュラー薄膜の室温光誘起巨大磁気抵抗効果 Reviewed

    水口将輝, 秋永広幸, 小野寛太, 尾嶋正治

    日本応用磁気学会誌   Vol. 25   page: 502 - 506   2001

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    DOI: 10.3379/jmsjmag.25.502

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  152. Electron localization in nanoscale MnAs dots on GaAs: a photoemission study

    Ono K, Mizuguchi M, Uragami T, Akinaga H, Fujioka H, Oshima M

    PHYSICA B   Vol. 284   page: 1778 - 1779   2000.7

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  153. Electron localization in nanoscale MnAs dots on GaAs: a photoemission study Reviewed

    K Ono, M Mizuguchi, T Uragami, H Akinaga, H Fujioka, M Oshima

    PHYSICA B   Vol. 284   page: 1778 - 1779   2000.7

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    We have investigated the electronic structure of MnAs dots on GaAs (100) by photoemission spectroscopy. MnAs dots are grown on the S-passivated GaAs by MBE. The size of the dots is 15 nm. In the valence band photoemission spectra of MnAs dots, the Fermi edge disappears, and there is no spectral intensity at the Fermi level. In the Mn 2p core level spectra of MnAs dots, we have observed a satellite structure which also reflects the 3d electron localization in the MnAs dots. (C) 2000 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0921-4526(99)02967-1

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  154. Fabrication and magnetotransport properties of nanoscaled MnSb dots

    Mizuguchi M, Akinaga H, Ono K, Oshima M

    JOURNAL OF APPLIED PHYSICS   Vol. 87 ( 9 ) page: 5639 - 5641   2000.5

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  155. Room-temperature photoinduced magnetoresistance effect in GaAs including MnSb nanomagnets

    Akinaga H, Mizuguchi M, Ono K, Oshima M

    APPLIED PHYSICS LETTERS   Vol. 76 ( 18 ) page: 2600 - 2602   2000.5

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  156. Fabrication and magnetotransport properties of nanoscaled MnSb dots Reviewed

    M Mizuguchi, H Akinaga, K Ono, M Oshima

    JOURNAL OF APPLIED PHYSICS   Vol. 87 ( 9 ) page: 5639 - 5641   2000.5

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    We report the fabrication and magnetotransport properties of nanoscaled clusters of manganese antimonide (MnSb) grown on sulfur-passivated GaA(001) substrates by molecular-beam-epitaxy (MBE). The typical diameter and height of dots were about 22 nm and 4 nm, respectively. Uniform dots in size were formed in a self-assembled mode. Magnetotransport properties of MnSb granular films were investigated, and the anisotropic magnetoresistance were observed at room temperature. Large jumps appeared at 9 K in magnetoresistance curves, and the jump structure depends on the sweep rate of the magnetic field. These magnetotransport properties describe well the magnetic behavior of MnSb dots. (C) 2000 American Institute of Physics. [S0021-8979(00)38308-6].

    DOI: 10.1063/1.372475

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  157. Room-temperature photoinduced magnetoresistance effect in GaAs including MnSb nanomagnets Reviewed

    H Akinaga, M Mizuguchi, K Ono, M Oshima

    APPLIED PHYSICS LETTERS   Vol. 76 ( 18 ) page: 2600 - 2602   2000.5

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    We show a photoinduced positive magnetoresistance (MR) effect (about 20%) under a low magnetic field (less than 0.1 T) at room temperature. The photoinduced MR effect has been observed in GaAs including nanoscale MnSb islands, when photons with the energy above the band gap of GaAs irradiated the sample. The photoinduced phenomena are due to an enhancement of tunneling probability between MnSb islands by photogenerated carriers in the GaAs matrix. (C) 2000 American Institute of Physics. [S0003-6951(00)02718-2].

    DOI: 10.1063/1.126421

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  158. Crystallographic and magneto-optical studies of nanoscaled MnSb dots grown on GaAs

    Mizuguchi M, Akinaga H, Ono K, Oshima M

    APPLIED PHYSICS LETTERS   Vol. 76 ( 13 ) page: 1743 - 1745   2000.3

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  159. Crystallographic and magneto-optical studies of nanoscaled MnSb dots grown on GaAs Reviewed

    M Mizuguchi, H Akinaga, K Ono, M Oshima

    APPLIED PHYSICS LETTERS   Vol. 76 ( 13 ) page: 1743 - 1745   2000.3

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    MnSb ultrathin films with the nominal thickness of 0-1.40 nm were grown on sulfur passivated GaAs substrates by molecular beam epitaxy. Atomic force microscopy analysis showed that MnSb formed nanosize clusters on the substrate, and the coalescence of the clusters occurred at the nominal thickness between 0.70 and 1.05 nm. The intensity of the polar magnetic circular dichroism of MnSb clusters suddenly increased when the nominal thickness reached the critical value of 1.05 nm. The coalescence among the dots can be correlated with the sharp increase of the magnetic circular dichroism intensity. (C) 2000 American Institute of Physics. [S0003-6951(00)01013-5].

    DOI: 10.1063/1.126153

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  160. Formation and structural investigation of MnSb dots on S-passivated GaAs(001) substrates

    Mizuguchi M, Akinaga H, Ono K, Oshima M

    JOURNAL OF CRYSTAL GROWTH   Vol. 209 ( 2-3 ) page: 552 - 555   2000.2

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  161. Molecular beam epitaxy of MnSb/MnAs multilayers on GaAs

    Ono K, Uragami T, Mizuguchi M, Fujioka H, Oshima M, Tanaka M, Akinaga H

    JOURNAL OF CRYSTAL GROWTH   Vol. 209 ( 2-3 ) page: 556 - 560   2000.2

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  162. The effect of S- and Se-passivation on MBE growth of MnAs thin films on GaAs(100) substrates

    Uragami T, Ono K, Mizuguchi M, Fujioka H, Tanaka M, Oshima M

    JOURNAL OF CRYSTAL GROWTH   Vol. 209 ( 2-3 ) page: 561 - 565   2000.2

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  163. Formation and structural investigation of MnSb dots on S-passivated GaAs(001) substrates Reviewed

    M Mizuguchi, H Akinaga, K Ono, M Oshima

    JOURNAL OF CRYSTAL GROWTH   Vol. 209 ( 2-3 ) page: 552 - 555   2000.2

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    We have succeeded in fabricating nanoscale manganese antimonide (MnSb) dots on GaAs substrates by molecular beam epitaxy. Sulfur passivated surfaces were used to decrease the surface energy and to form MnSb dots on the substrate. Morphologies of the dots were investigated by atomic force microscopy, Different growth modes which arose from a difference in growth temperatures were observed, (C) 2000 Elsevier Science B.V, All rights reserved.

    DOI: 10.1016/S0022-0248(99)00618-1

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  164. Molecular beam epitaxy of MnSb/MnAs multilayers on GaAs Reviewed

    K Ono, T Uragami, M Mizuguchi, H Fujioka, M Oshima, M Tanaka, H Akinaga

    JOURNAL OF CRYSTAL GROWTH   Vol. 209 ( 2-3 ) page: 556 - 560   2000.2

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    We have investigated the initial growth of MnSb and MnAs films and multilayers on GaAs(1 0 0) and (1 1 1)B substrates by molecular beam epitaxy (MBE) and successfully grown epitaxial MnSb/MnAs multilayers on GaAs(1 1 1)B. We propose a possibility of the novel heat-induced giant magnetoresistance (GMR) effect in the MnSb/MnAs multilayer system. (C) 2000 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-0248(99)00619-3

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  165. The effect of S- and Se-passivation on MBE growth of MnAs thin films on GaAs(100) substrates Reviewed

    T Uragami, K Ono, M Mizuguchi, H Fujioka, M Tanaka, M Oshima

    JOURNAL OF CRYSTAL GROWTH   Vol. 209 ( 2-3 ) page: 561 - 565   2000.2

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    Ferromagnetic MnAs thin films were grown on clean, S- and Se-passivated GaAs(1 0 0) substrates by molecular beam epitaxy (MBE). Growth modes of MnAs films on GaAs substrates depend on the surface treatment. On the clean and the Se-passivated surfaces MnAs films grow by a layer-by-layer mode, whereas on the S-passivated surface MnAs films grow by an island growth mode, and as a result polycrystalline films are obtained. Photoelectron spectroscopy study revealed that the Se overlayer on the Se-passivated GaAs substrates prevented Ga interdiffusion. We also found that the saturation magnetization of MnAs films on the Se-passivated surface was slightly larger than that on the clean and the S-passivated surfaces. This difference can be explained by the role of Se overlayer in preventing interdiffusion between MnAs and GaAs. (C) 2000 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0022-0248(99)00620-X

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  166. Room-temperature thousandfold magnetoresistance change in MnSb granular films: Magnetoresistive switch effect

    Akinaga H, Mizuguchi M, Ono K, Oshima M

    APPLIED PHYSICS LETTERS   Vol. 76 ( 3 ) page: 357 - 359   2000.1

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  167. Room-temperature thousandfold magnetoresistance change in MnSb granular films: Magnetoresistive switch effect Reviewed

    H Akinaga, M Mizuguchi, K Ono, M Oshima

    APPLIED PHYSICS LETTERS   Vol. 76 ( 3 ) page: 357 - 359   2000.1

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    A huge positive magnetoresistance effect has been discovered in MnSb granular films. Granular film consisting of nanoscale MnSb dots that are grown on a sulfur-passivated GaAs (001) substrate by molecular-beam epitaxy, then covered with an Sb thin layer, exhibits magnetic-field-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied to the film, more than 1000% change in the current, which we term magnetoresistive switch, is driven by the magnetoresistance effect under a relatively low magnetic field (less than 0.5 T) at room temperature. (C) 2000 American Institute of Physics. [S0003-6951(00)04303-5].

    DOI: 10.1063/1.125753

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  168. Enormous magnetoresistance effect in hybrid ferromagnetic-nanocluster/semiconductor films Reviewed

    H. Akinaga, M. Mizuguchi, K. Ono, M. Oshima

    Transactions of Materials Research Society of Japan   Vol. 25   page: 1119 - 1122   2000

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  169. MnSbグラニュラー構造における室温超巨大磁気抵抗効果 Reviewed

    秋永広幸, 水口将輝, 小野寛太, 尾嶋正治

    日本応用磁気学会誌   Vol. 24   page: 451 - 454   2000

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    DOI: 10.3379/jmsjmag.24.451

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  170. MnSbグラニュラー薄膜の作製と磁気光学特性 Reviewed

    水口将輝, 秋永広幸, 小野寛太, 尾嶋正治

    日本応用磁気学会誌   Vol. 24   page: 499 - 502   2000

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    DOI: 10.3379/jmsjmag.24.499

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  171. Enhanced Kerr rotation in electrodeposited nickel films

    Attenborough K, De Boeck J, Celis JP, Mizuguchi M, Akinaga H

    IEEE TRANSACTIONS ON MAGNETICS   Vol. 35 ( 5 ) page: 2985 - 2987   1999.9

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  172. Enhanced Kerr rotation in electrodeposited nickel films Reviewed

    K Attenborough, J De Boeck, JP Celis, M Mizuguchi, H Akinaga

    IEEE TRANSACTIONS ON MAGNETICS   Vol. 35 ( 5 ) page: 2985 - 2987   1999.9

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    High quality nickel films were electrodeposited directly onto n-GaAs using galvanostatic control. It was seen that by varying the current density the crystallographic orientation of the films could be controlled. For a current density of 15 mA/cm(2), a highly dominant (220) crystallographic orientation was obtained, Magnetic measurements revealed a strong uniaxial anisotropy in these films, Moreover, Kerr spectroscopy measurements (1.4 to 4.5 eV) showed an enhanced Kerr rotation of -0.17 degrees at 3.2 eV, which may be attributed to the strong magnetic anisotropy and the exceptional crystal quality of the films.

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  173. Formation of low-dimensional structures of manganese pnictides Reviewed

    K. Ono, T. Uragami, M. Mizuguchi, H. Fujioka, M. Oshima, M. Tanaka, H. Akinaga, Y. Watanabe

    Journal of the Magnetics Society of Japan   Vol. 23   page: 688 - 690   1999

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    DOI: 10.3379/jmsjmag.23.688

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  174. M-2,M-3 edge core-level magnetic circular dichroism measurements of Cu/Co multilayers Reviewed

    S Kawaguchi, K Ono, K Horiba, M Mizuguchi, S Hayakawa, H Fujioka, T Koide, H Miyauchi, N Nakajima, H Takenaka, M Oshima

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   Vol. 38   page: 419 - 422   1999

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    We have carried out the magnetic circular dichroism (MCD) measurements in the VUV region near M-2,M-3 absorption edges of Cu and Co for Cu/Co multilayers in order to investigate the perpendicular magnetization of the system. Circularly polarized SR light was incident almost normal to the sample surface and the reflected light was detected, corresponding to the information about perpendicular magnetic moments. The MCD spectrum of the magnetic layers at Co M-2,M-3 edges showed one negative peak. Although Cu is non-magnetic, a similar MCD profile was obtained for Cu M-2,M-3 edges. These results indicate that the perpendicular magnetic moments of non-magnetic Cu are induced near the Cu/Co interfaces of multilayers and the directions of the magnetic moments in Cu and Co layers are parallel with each other along the direction of applied magnetic field.

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  175. M-2,M-3 edge core-level magnetic circular dichroism measurements of Cu/Co multilayers

    Kawaguchi S, Ono K, Horiba K, Mizuguchi M, Hayakawa S, Fujioka H, Koide T, Miyauchi H, Nakajima N, Takenaka H, Oshima M

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   Vol. 38   page: 419 - 422   1999

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  176. Growth of MnAs on S- and Se-passivated GaAs substrates Reviewed

    T. Uragami, K. Ono, M. Mizuguchi, T. Mano, H. Fujioka, M. Oshima, M. Tanaka, Y. Watanabe

    Journal of the Magnetics Society of Japan   Vol. 23   page: 694 - 696   1999

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    DOI: 10.3379/jmsjmag.23.694

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  177. Formation of MnAs dots on S-passivated GaAs(100) substrates Reviewed

    K. Ono, M. Mizuguchi, T. Uragami, T. Mano, H. Fujioka, M. Oshima, M. Tanaka, Y. Watanabe

    Journal of the Magnetics Society of Japan   Vol. 23   page: 691 - 693   1999

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    DOI: 10.3379/jmsjmag.23.691

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  178. Photoelectron spectroscopy and magnetic properties of manganese pnictides nanocrystals formed on passivated GaAs substrates

    Oshima M, Ono K, Mizuguchi M, Uragami T, Fujioka H, Tanaka M, Watanabe Y

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS   Vol. 38   page: 373 - 376   1999

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  179. Photoelectron spectroscopy and magnetic properties of manganese pnictides nanocrystals formed on passivated GaAs substrates Reviewed

    M Oshima, K Ono, M Mizuguchi, T Uragami, H Fujioka, M Tanaka, Y Watanabe

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   Vol. 38   page: 373 - 376   1999

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    We first report the formation and magnetic properties of MnAs and MnSb nanocrystals by "super Volmer-Weber epitaxy" utilizing very low surface energy substrates such as sulfur-passivated GaAs substrates. On the S-passivated GaAs surface MnAs dots with the size of about 16 nm and the density of 2x10(10) cm(-2) were successfully grown. SQUID analysis of these dots showed partly vertical easy magnetization axis. However, on the Se-GaAs surface, no MnAs dots were grown. SRPES revealed that Se atoms were segregated to the MnAs surface, probably playing a role of surfactant for the layer growth mode.

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Books 5

  1. Magnetic nanostructures for energy harvesting using magnetothermoelectric effects Reviewed

    Masaki Mizuguchi( Role: Sole author)

    Elsevier  2021 

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    Total pages:13   Responsible for pages: 750-762   Language:English Book type:Scholarly book

  2. Energy harvesting and generation system - Overview Reviewed

    Masaki Mizuguchi( Role: Sole author)

    Elsevier  2021 

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    Total pages:2   Responsible for pages:713-714   Language:English

  3. "L10-FeNi超格子材料の磁気特性", 次世代永久磁石の開発最前線

    水口将輝, 小嶋隆幸, 高梨弘毅( Role: Joint author)

    エヌ・ティー・エス  2019 

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  4. 単原子交互積層法による新規磁気異方性材料L10-FeNi薄膜の作製と特性評価, 磁性材料・部品の最新開発事例と応用技術

    高梨弘毅, 水口将輝, 藏裕彰, 後藤翔( Role: Joint author)

    技術情報協会  2018 

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  5. Lecture Notes in Physics

    Akinaga, M. Mizuguchi, K. Nagao, Y. Miura, M. Shirai( Role: Joint author ,  "Materials Design and Molecular-Beam Epitaxy of Half-Metallic Zinc-Blende CrAs and the Heterostructures" (pp. 293-311))

    Springer-Verlag GmbH  2005 

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MISC 45

  1. ナノ構造における異常ネルンスト効果の物理と応用の新展開 Invited Reviewed

    水口将輝

    応用物理     2021.2

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  2. 熱磁気効果をベースとした熱電材料の新展開 Invited Reviewed

    水口将輝

    まてりあ   Vol. 60   page: 558 - 561   2021

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  3. 新分野創成利用課題報告「ナノスケール実スピンデバイス開発に向けた新しい放射光利用」

    小野 輝男、岡本 聡、千葉 大地、水口 将輝、壬生 攻

    SPring-8/SACLA 利用者情報/2021 年春号     2021

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  4. Synthesis of ferromagnetic phase of Mn<sub>53</sub>Zn<sub>2</sub>Al<sub>45</sub> by in-field annealing

    三井好古, 小林領太, 梅津理恵, 高橋弘紀, 水口将輝, 小山佳一

    東北大学金属材料研究所強磁場超伝導材料研究センター年次報告   Vol. 2019   2020

  5. Evaluation of magnetic field effects on synthesis of ferromagnetic materials

    小林領太, 高永悠大, 三井好古, 高木観雄, 小山佳一, 高橋弘紀, 梅津理恵, 水口将輝

    東北大学金属材料研究所新素材共同研究開発センター共同利用研究報告書(CD-ROM)   Vol. 2018   2019

  6. Physics of anomalous Nernst effect in ferromagnetic materials

    水口 将輝, 長谷川 浩太, 高梨 弘毅

    社団法人日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan   Vol. 220   page: 1 - 5   2018.11

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  7. Magnetic properties of (Mn,Zn)-Al alloys obtained by in-field annealing

    三井好古, 高木観雄, 小林領太, 小山佳一, 梅津理恵, 高橋弘紀, 水口将輝

    東北大学金属材料研究所新素材共同研究開発センター共同利用研究報告書(CD-ROM)   Vol. 2017   2018

  8. Mn-Al-Znに対する磁場中熱処理効果

    小林領太, 高木観雄, 三井好古, 梅津理恵, 高橋弘紀, 水口将輝, 小山佳一

    東北大学金属材料研究所強磁場超伝導材料研究センター年次報告   Vol. 2017   2018

  9. パルスレーザー蒸着(PLD)法を用いたMgO基板上L1<sub>0</sub>-FeNiの作製

    齊藤真博, 伊藤久晃, 落合順也, 森あゆみ, 鈴木雄太, 富田正樹, 宮町俊生, 小森文夫, 小金澤智之, 水口将輝, 高梨弘毅, 小嗣真人

    日本磁気学会学術講演概要集   Vol. 41st   2017

  10. Magnetic properties of as-melt Mn-Al alloys annealed in magnetic field

    三井好古, 小林領太, 小山佳一, 梅津理恵, 高橋弘紀, 水口将輝

    東北大学金属材料研究所新素材共同研究開発センター共同利用研究報告書(CD-ROM)   Vol. 2016   2017

  11. 単原子交互積層法による新規磁気異方性材料L10-FeNi薄膜の作製と特性評価

    水口将輝, 小嶋隆幸, 田代敬之, 高梨弘毅

        2017

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  12. Uniaxial magnetic anisotropy of tetragonal FeCo based alloyt films and its perspective to new permanent magnet

    水口将輝, 高梨弘毅, 堀田善治, 白井正文, 小嗣真人

    電気学会マグネティックス研究会資料   Vol. MAG-16 ( 178-196 ) page: 85‐88   2016.11

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  13. Magnetic properties of Mn-based magnetic materials prepared by in-field heat treatment

    三井好古, 小林領太, 小山佳一, 梅津理恵, 高橋弘紀, 水口将輝

    東北大学金属材料研究所新素材共同研究開発センター共同利用研究報告書   Vol. 2015   2016

  14. 第三元素を添加したFe/Ni薄膜の規則化現象

    田代敬之, 水口将輝, 小金澤智之, 鈴木英伸, 三浦良雄, 辻川雅人, 白井正文, 高梨弘毅

    日本磁気学会学術講演概要集   Vol. 40th   2016

  15. [Fe-X/Ni](X=Ti,V)多層膜のL1<sub>0</sub>規則化

    田代敬之, 水口将輝, 小金澤智之, 鈴木英伸, 三浦良雄, 辻川雅人, 白井正文, 高梨弘毅

    日本金属学会講演概要(CD-ROM)   Vol. 159th   2016

  16. 磁性ナノ超構造の創製とスピンデバイスへの応用

    水口将輝

    まぐね     2016

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  17. CoとNiの膜厚比を変えたCo/Niエピタキシャル多層膜における異常ネルンスト効果

    鈴木英伸, 水口将輝, 小金澤智之, 高梨弘毅

    日本金属学会講演概要(CD-ROM)   Vol. 159th   2016

  18. Ti添加によるL1<sub>0</sub>-FeNi規則合金薄膜の作製と評価

    田代敬之, 水口将輝, 小金澤智之, 三浦良雄, 辻川雅人, 白井正文, 鈴木英伸, 高梨弘毅

    日本金属学会講演概要(CD-ROM)   Vol. 158th   2016

  19. スパッタ法と急速昇温熱処理によるL1<sub>0</sub>-FeNi相の形成

    田代敬之, 水口将輝, 小金澤智之, 佐藤和久, 今野豊彦, 高梨弘毅

    日本磁気学会学術講演概要集   Vol. 39th   2015

  20. 酸化物基板上にスパッタ成膜したFeNi薄膜

    田代敬之, 水口将輝, 高梨弘毅, 小金澤智之, 小嗣真人, 佐藤和久, 今野豊彦

    日本金属学会講演概要(CD-ROM)   Vol. 156th   2015

  21. Anomalous Nernst effect in L1(0) type Mn-Ga alloy thin films.

    M. Mizuguchi, M. Inoue, S. Mizukami, K. Takanashi

    2015 IEEE MAGNETICS CONFERENCE (INTERMAG)     2015

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  22. Artificial fabrication and characterization of L1(0)-ordered FeNi thin films.

    K. Takanashi, M. Mizuguchi, T. Kojima, T. Tashiro

    2015 IEEE MAGNETICS CONFERENCE (INTERMAG)     2015

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  23. 規則合金スピントロニクス材料の最近の発展

    窪田崇秀, 関剛斎, 水口将輝, 高梨弘毅

    電気学会マグネティックス研究会     2015

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  24. スパッタ法により作製したFe/Ni多層膜への急速昇温熱処理によるL1<sub>0</sub>相の形成

    田代敬之, 水口将輝, 高梨弘毅, 小金澤智之, 小嗣真人

    日本金属学会講演概要(CD-ROM)   Vol. 155th   2014

  25. スパッタ法によるMgO(001)単結晶基板上へのL10-FeNi規則合金薄膜の作製

    田代敬之, 田代敬之, 水口将輝, 小嶋隆幸, 佐藤和久, 今野豊彦, 高梨弘毅, 小金澤智之, 小嗣真人, 大槻匠

    日本金属学会講演概要(CD-ROM)   Vol. 154th   2014

  26. 強磁性金属薄膜における熱磁気効果

    水口将輝, 長谷川浩太, 桜庭裕弥, 内田健一, 齋藤英治, 窪田崇秀, 水上成美, 宮崎照宣, 高梨弘毅

    日本磁気学会研究会資料   Vol. 193rd   page: 7 - 11   2013.12

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  27. Temperature dependence of anomalous Nernst effect in perpendicularly magnetized metallic thin films

    Mizuguchi Masaki, Hasegawa Kota, Uchida Ken-ichi, Saitoh Eiji, Takanashi Koki

    Meeting abstracts of the Physical Society of Japan   Vol. 68 ( 2 ) page: 401 - 401   2013.8

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  28. 高い磁気異方性を有するL10型FePtおよびL10型FeNi規則合金薄膜

    小嶋隆幸, 関剛斎, 水口将輝, 高梨弘毅

    セラミックス     2013

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  29. L1<sub>0</sub>型FeNi規則合金(tetrataenite)の磁気異方性

    小嶋隆幸, 荻原美沙子, 水口将輝, 田代敬之, 高梨弘毅, 小嗣真人, 小金澤智之, 大槻匠

    日本金属学会講演概要(CD-ROM)   Vol. 153rd   2013

  30. 19aCC-6 Systematic investigation and property evaluation of anomalous Nernst effect in ferromagnetic metal thin films

    Hasegawa Kota, Mizuguchi Masaki, Uchida Ken-ichi, Saitoh Eiji, Takanashi Koki

    Meeting abstracts of the Physical Society of Japan   Vol. 67 ( 2 ) page: 412 - 412   2012.8

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  31. 24pBG-9 Microscopic origin of anomalous Nernst effect in ferromagnetic metallic thin films

    Mizuguchi Masaki, Hasegawa Kohta, Uchida Ken-ichi, Saitoh Eiji, Takanashi Koki

    Meeting abstracts of the Physical Society of Japan   Vol. 67 ( 1 ) page: 506 - 506   2012.3

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  32. 人工合成L1<sub>0</sub>型FeNi薄膜の磁気異方性と構造

    小嶋隆幸, 荻原美沙子, 水口将輝, 高梨弘毅, 小嗣真人, 小金澤智之, 大槻匠

    日本金属学会講演概要(CD-ROM)   Vol. 151st   2012

  33. 単原子層制御交互蒸着により作製したL1<sub>0</sub>型FeNi規則合金薄膜の磁気異方性

    小嶋隆幸, 荻原美沙子, 水口将輝, 田代敬之, 高梨弘毅, 小嗣真人, 小金澤智之, 大槻匠, 大河内拓雄

    表面科学学術講演会講演要旨集   Vol. 32nd   2012

  34. 貴金属フリー高磁気異方性材料L10 型FeNi 規則合金の作製と評価

    水口将輝, 小嶋隆幸, 高梨弘毅, 小嗣真人, 白井正文

    まてりあ     2012

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  35. 人工合成L1<sub>0</sub>型FeNi薄膜の規則度評価および磁気異方性との関係

    小嶋隆幸, 小嶋隆幸, 水口将輝, 小金澤智之, 大坂恵一, 小嗣真人, 高梨弘毅

    日本金属学会講演概要   Vol. 148th   2011

  36. 単原子層交互積層法により作製したL1<sub>0</sub>型FeNi薄膜の構造と磁気特性の関係

    小嶋隆幸, 小嶋隆幸, 小嶋隆幸, 水口将輝, 小金澤智之, 大坂恵一, 小嗣真人, 高梨弘毅

    日本金属学会講演概要(CD-ROM)   Vol. 149th   2011

  37. L10型FeNi薄膜の創製とその特性評価

    水口将輝, 小嶋隆幸, 関谷茂樹, 高梨弘毅

    日本磁気学会 第177回研究会資料     page: 13 - 17   2011

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  38. 貴金属フリー高磁気異方性材料L10 型FeNi 規則合金の作製と評価

    水口将輝, 小嶋隆幸, 高梨弘毅, 小嗣真人, 白井正文

    まてりあ     2011

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    DOI: 10.2320/materia.50.389

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  39. 金属スピントロニクスと表面科学

    水口将輝

    表面科学     2011

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    DOI: 10.1380/jsssj.32.145

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  40. 格子不整合を用いた磁性ナノ粒子集合体の創製

    水口将輝, 大道悟, 高梨弘毅

    日本磁気学会第172会研究会資料「ナノ磁性体・磁性素子の作製〜トップダウンとボトムアップ〜」     page: 31 - 35   2010.5

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  41. 完全スピン偏極強磁性体の物質設計と合成

    秋永広幸, 水口将輝, 眞砂卓史, 小野寛太, 尾嶋正治, 白井正文

    日本応用磁気学会誌   Vol. 26   page: 67 - 72   2002

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  42. GaAs/MnSbグラニュラー構造における磁気抵抗スイッチ効果

    秋永広幸, 水口将輝, 小野寛太, 尾嶋正治

    応用物理   Vol. 70   page: 313 - 316   2001

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    DOI: 10.11470/oubutsu1932.70.313

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  43. 新完全スピン偏極強磁性体ー閃亜鉛鉱型CrAs

    秋永広幸, 水口将輝, 眞砂卓史, 小野寛太, 尾嶋正治, 白井正文

    固体物理   Vol. 36   page: 587 - 592   2001

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  44. 金属 / 半導体ハイブリッド超薄膜で出現した超巨大磁気抵抗効果ー磁気抵抗スイッチ効果ー

    秋永広幸, 水口将輝

    化学と工業   Vol. 54   page: 814 - 816   2001

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  45. 半導体表面への磁性ナノ構造の成長と物性

    尾嶋正治, 小野寛太, 水口将輝, 藤岡洋, 田中雅明, 秋永広幸

    日本応用磁気学会誌   Vol. 24   page: 67 - 73   2000

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▼display all

KAKENHI (Grants-in-Aid for Scientific Research) 25

  1. ナノ超構造がもたらす熱・スピン機能変革

    Grant number:21H05016  2021.7 - 2026.3

    科学研究費助成事業  基盤研究(S)

    水口 将輝

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    Authorship:Principal investigator 

    Grant amount:\193570000 ( Direct Cost: \148900000 、 Indirect Cost:\44670000 )

  2. スピンカロリトロニクスを基軸とした高効率テラヘルツ波発生機能の開拓

    2019.2 - 2022.3

    日本学術振興会  国際共同研究加速基金 (国際共同研究強化(A)) 

    研究代表者: 水口 将輝

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  3. ナノ超構造体を基盤とした革新的ナノスピンカロリトロニクス機能の創出

    2017.4 - 2021.3

    日本学術振興会  科学研究費補助金 基盤研究 (A) 

    研究代表者: 水口 将輝

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  4. ナノ超空間を利用した熱・スピン・電界交差相関による高効率エネルギー変換材料の創製

    2015.10 - 2021.9

    科学技術振興機構  戦略的創造研究推進事業 (CREST) 

    研究代表者: 水口 将輝

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    Authorship:Principal investigator  Grant type:Competitive

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  5. 熱磁気効果を活用した革新的環境発電技術の研究開発

    2019.12 - 2020.11

    公益財団法人カシオ科学振興財団  研究助成 特別テーマ 

    水口 将輝

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    Authorship:Principal investigator  Grant type:Competitive

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  6. スピンを基軸とした熱電変換現象における電界変調法の確立と熱電素子への応用

    2019.10 - 2020.3

    村田学術振興財団  研究助成 

    水口 将輝

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  7. Efficient terahertz emission based on spin caloritronics

    Grant number:18KK0377  2019 - 2021

    Fund for the Promotion of Joint International Research (Fostering Joint International Research (A))

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    Authorship:Principal investigator 

    Grant amount:\15600000 ( Direct Cost: \12000000 、 Indirect Cost:\3600000 )

  8. ナノ超構造体を基盤とした革新的ナノスピンカロリトロニクス機能の創出

    Grant number:17H01052  2017.4 - 2020.3

    水口 将輝

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    Authorship:Principal investigator 

    Grant amount:\44070000 ( Direct Cost: \33900000 、 Indirect Cost:\10170000 )

    本研究の目的は、固体金属やイオン液体において、巨大熱電効果などの革新的な熱磁気機能を創出することである。我々はこれまでに、いくつかの熱磁気効果に着目し、マクロなサイズにおいてそれらの特性を明らかにし、新機能創出の可能性を示してきた。そこで本研究では、試料をナノスケールまで微小化することにより、熱とスピンの相関を顕わにし、効率的にスピンカロリトロニクス機能を引き出すことをねらう。今年度は、ナノデバイスにおける異常ネルンスト効果の電界制御を試みた。イオン液体を用いた電圧印加により、ネルンスト電圧の大きさを室温で制御することに成功した。3 Kの温度差を付与したナノデバイスに+2 Vのゲート電圧を印加した結果、ネルンスト電圧が顕著に増加することが分かった。また、ナノサイズ量子ドットを利用した電界効果トランジスタの開発も行った。量子ドット薄膜の作製法の最適化を行うことにより、電子移動度が量子ドット電界効果トランジスタの中での最大値に匹敵する値まで至り、従来のCCDと比較しても100倍以上高感度の光センサが実現した。トランジスタの電流が立ち上がる閾値電圧を100 V以上制御することができるデバイスも実現した。さらに、螺旋磁性体中の熱電効果の研究を行い、磁化構造の螺旋軸方向の非等方的なスピン波拡散の存在を明らかにした。特に、反強磁性相互作用を有する螺旋磁性体中では、スピン波の局在効果による熱拡散の抑制を見出し、螺旋磁性体を用いた熱整流が可能であることを明らかにした。
    異常ネルンスト効果の微視的機構解明とナノスケール巨大熱電機能素子の創製などがおおむね計画通りに進んでいる。また、当初の目標であった室温における異常ネルンスト効果の電界制御にも成功した。さらに、ナノサイズ量子ドットにおける熱電効果の電界制御にむけた素子構造の最適化や、反強磁性相互作用を有する螺旋磁性体中での熱整流作用に関する理論構築も進んでおり、その進捗度もおおむね順調であるため。
    今後は、レーザーを用いた熱励起異常ネルンスト効果の時間分解測定について、加速的に研究を進める。ネルンスト効果の生じる時間スケールや、スピン歳差運動とネルンスト効果の相関などについて、詳細な測定を進める。また、ナノサイズ量子ドットにおける熱電効果の測定についても、トランジスタデバイスを完成させ、その電界制御に関する実験を進める。さらに、反強磁性相互作用を有する螺旋磁性体中での熱整流効果についても、理論を参考にしながら、実験的な検証を進める。

  9. スピントロニクスデバイスを基盤とした局所原子配列と磁気機能の相関解明

    Grant number:17H05208  2017.4 - 2019.3

    新学術領域研究(研究領域提案型)

    水口 将輝

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    Authorship:Principal investigator 

    Grant amount:\6500000 ( Direct Cost: \5000000 、 Indirect Cost:\1500000 )

    本研究の目的は、スピントロニクスデバイスにおいて極めて重要なテーマである、“局所原子配列と磁気機能の相関”を解明するため、その場・非破壊観察技術を通した三次元活性サイトの局所的なイメージングを行うことである。金属多層膜などのヘテロ界面における局所的な原子配列は、磁気機能に対する活性サイトであり、特異な磁気異方性が発現していると考えられる。そのため、多層膜の深さ方向に対して原子分解能を有する各種ホログラフィー技術を駆使し、最表面から埋もれた界面の情報を取得することにより、磁気異方性のミクロなメカニズムの解明が期待される。実際のスピントロニクス素子における局所イメージングを駆使することにより、元素ごとの特性に立脚したスピントロニクスの学理の構築を図るだけでなく、より応用に即したデバイス特性の向上を目指す。今年度は、トンネル磁気抵抗素子に電圧を印加した状態で蛍光X線ホログラフィを測定した。電圧を印加することにより、磁気異方性が変化するメカニズムを解明することを試みた。その結果、1 Vの電圧を印加したときのホログラフィパターンに、電圧印加に起因すると思われる変化が観測された。これは、電圧の印加により、試料のFe原子周辺の局所的な原子配置が変化したことを示唆する結果である。また、高い磁気抵抗比を示すトンネル磁気抵抗素子の障壁層材料である、スピネル薄膜の電子線ホログラフィを測定した。その結果、O 1s、Mg 2s、Al 2sの光電子ホログラムパターンの強度分布が異なることが明らかになった。
    平成30年度が最終年度であるため、記入しない。
    平成30年度が最終年度であるため、記入しない。

  10. スピントロニクスデバイスを基盤とした局所原子配列と磁気機能の相関解明

    2017.4 - 2019.3

    日本学術振興会  科学研究費補助金 新学術領域研究(研究領域提案型) 

    水口 将輝

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    Authorship:Principal investigator  Grant type:Competitive

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  11. Creation of L10-FeNi supermagnet

    Grant number:16H03873  2016.4 - 2019.3

    Kotsugi Masato

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    Authorship:Coinvestigator(s) 

    We here studied artificial fabrication of L10-type FeCo ordered alloy. (1) The improvement of PLD by automatic control technique. (2) The investigation of morphology and magnetic property in fundamental L10-FeNi system. (3) The fabrication and characterization of L10-FeCo using periodic buffer layer.
    As a result, we improved stability of PLD system, and the formation mechanism in PLD-L10-FeNi was clarified. The use of buffer layer could maintain L10 phase in FeCo system, and the substitution from Cu to Ni improves magnetic properties.

  12. ナノスピンイオニクスの開拓

    2014.4 - 2017.3

    日本学術振興会  科学研究費補助金 挑戦的萌芽研究 

    水口 将輝

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    Authorship:Principal investigator  Grant type:Competitive

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  13. Development of nano spin-ionics

    Grant number:26600069  2014.4 - 2017.3

    MIZUGUCHI MASAKI

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    Authorship:Principal investigator 

    Grant amount:\3900000 ( Direct Cost: \3000000 、 Indirect Cost:\900000 )

    This research aimed to clarify the scientific prinsiple of nano spin-ionics and to demonstrate an application to functional electronics. Electric effects in a solid electrolyte including a magnetic ion were investigated. The role of ions for the magnetism in carbon-based materials was also investigated, and it was proved that addition of ions paves the way for inducing magnetization in the materials.

  14. New development of ordered-alloy materials for spintronics

    Grant number:25220910  2013.5 - 2018.3

    TAKANASHI Koki

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    The purpose of this research project was the development of ordered alloys for high performance and multi-functional spintronics devices and their application to spincaloritronics. We successfully improved the giant magnetoresistance (GMR) effect for the device with L21-ordered Co2(FeMn)Si full-Heusler alloy, and observed room temperature GMR using C1b-ordered NiMnSb half-Heusler alloy. We also achieved high magnetic anisotropy and low magnetic damping simultaneously for L11-type-stacked CoNi. In addition, we revealed the material dependence of anomalous Nernst effect, leading to the guiding principle for high spincaloritronic functionality.

  15. Microscopic origin of anomalous Nernst effect in perpendicularly magnetized thin films

    Grant number:24656002  2012.4 - 2014.3

    MIZUGUCHI MASAKI

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    Authorship:Principal investigator 

    Grant amount:\4030000 ( Direct Cost: \3100000 、 Indirect Cost:\930000 )

    This research aimed to clarify the physical mechanism of anomalous Nernst effect and to demonstrate an application of the effect to thermoelectric conversion devices. Magnetic anisotropy dependence and temperature dependence of anomalous Nernst effect were precisely investigated. The thermopile device including FePt wires enhanced the anomalous Nernst voltage effectively, which paves the way for realizing novel thermoelectric applications employing the anomalous Nernst effect.

  16. Development of high efficiency oscillators and detectors using nano-spin superstructures

    Grant number:23360004  2011.4 - 2014.3

    MIZUGUCHI MASAKI

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    Authorship:Principal investigator 

    Grant amount:\20930000 ( Direct Cost: \16100000 、 Indirect Cost:\4830000 )

    This research aimed to develop ultimate spin oscillators and detectors with high Q-values and high efficiency. To realize the purpose, nano-scaled spin-superstructures including ferromagnetic nano-dot arrays were fabricated. The influence of the ac spin current injection on spin torque oscillation has been also investigated within the framework of macro-spin model. Moreover, oscillation spectra were measured for actual nano-scaled GMR devices with large magnetoresistance to develop novel oscillation devices.

  17. local magnetic resonance excitation by using scanning spin injection probe

    Grant number:23360017  2011.4 - 2014.3

    AN Toshu

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    Scanning microwave probe, which can inject spin locally and apply spin torque to the magnet, has developed. Very thin high-frequency coaxial cable was used as the microwave source and detector of up to 10 GHz, and local excitation and detection of spin transfer torque oscillation was studied on the magnetic tunnel junction layers by injecting spin from the probe.

  18. Fabrication of multi-functional ferromagnetic ordered alloys by monoatomic layer deposition

    Grant number:22246087  2010 - 2012

    TAKANASHI Koki

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    Ordered alloys show various excellent magnetic properties, and they are promising as materials for next-generation electronics. From a viewpoint of application to magnetic storage technology, it is expected to develop new ordered alloys with multi-functionalities. In this study, we have attempted to fabricate novel ordered alloys with a high magnetic anisotropy, a high spin-polarization, and a low magnetic damping constant by employing a monoatomic layer deposition method. A stacked structure with L1_0-type FePt, CoPt and Co_2MnSi and an L1_0-type FeNi thin films were successfully fabricated, and various properties of the materials were investigated.

  19. Search for materials with giant anomalous Nernst effect at room temperature

    Grant number:22656002  2010 - 2011

    TAKANASHI Koki

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    Authorship:Collaborating Investigator(s) (not designated on Grant-in-Aid) 

    This study aimed to search for materials with giant anomalous Nernst effect at room temperature with the hypothesis that the effect was brought by the inverse spin-Hall effect of spin current generated by the temperature difference. We focused on half-metallic Heusler alloys with high spin polarization and the L10-type ordered alloys such as FePt with high magnetic anisotropy. The anomalous Nernst effect and the spin-Seebeck effect of these materials were systematically measured, and the relation between the two effects was investigated, which leads to the development of materials with giant anomalous Nernst effect at room temperature.

  20. Spin relaxation time in low dimensional nanostructures and its application to spintronic devices

    Grant number:20360002  2008 - 2010

    MITANI Seiji

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    Authorship:Coinvestigator(s) 

    The understanding of spin relaxation of conduction electrons is of particular interest for the development of spintronic devices. In this study, we investigated spin relaxation in low dimensional systems such as nanoparticles and ultrathin films by spin dependent transport measurements. While enhancement of spin relaxation time was observed in nanoparticles, such behavior was not obtained in ultrathin films. The difference possibly comes from the fact that electronic states in ultrathin films are not quantized in the in-plane directions. Simple model calculations were also performed for double-barrier magnetic tunnel junctions with enhanced spin relaxation time.

  21. Development of frequency-modulation type oscillation devices using perpendicular magnetic anisotropy and spin mode-lock

    Grant number:20686001  2008 - 2010

    MIZUGUCHI Masaki

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    Authorship:Principal investigator 

    Grant amount:\19110000 ( Direct Cost: \14700000 、 Indirect Cost:\4410000 )

    This research aimed to develop ultimate spin oscillation devices with high Q-value in which frequency modulation is possible, and an external magnetic field is not needed. To realize the purpose, nano-scaled magnetic superstructures including full-epitaxial crystals were fabricated. Then, high frequency spin response of these elements was measured, and oscillation conditions were investigated. Moreover, oscillation spectra were measured for actual nano-scaled devices with large magnetoresistance to develop novel oscillation devices.

  22. Fabrication of heghly efficient spin source materials by nanostructure control

    Grant number:19048004  2007 - 2010

    TAKANASHI Koki

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    Authorship:Coinvestigator(s) 

    Fabrication of highly efficient spin source aterials is an important issue for creation and control of spin current that is the flow of spin angular momentum. In this project, we fabricate highly spin-polarized / highly efficient spin soruce by nanostructure control. We achieve large magnetoresistance ratio at room temperature for giant magnetoresistance pillars with full-Heusler Co_2MnSi layers. We also successfully observed giant spin Hall effect in nanostructured devices with a Au Hall cross and an FePt perpendicular spin inhector, and carried out the systematic investigation of spin Hall effect in impurity doped-Au. In addision, the enhancement of spin relaxation time was observed in nanoparticles by measuring the magneto-transport properties in Fe, Cr, and Au nanoparticles.

  23. Fabrication of L10 type ordered alloy with high uniaxial magnetic anisotropy by alternative atomic monolayer deposition

    Grant number:19360311  2007 - 2009

    TAKANASHI Koki

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    Authorship:Coinvestigator(s) 

    The recording density of magnetic storages such as a hard disc equipped in a personal computer is now rapidly increasing, and a volume of one bit is getting smaller and smaller. Inexpensive magnetic materials with high uniaxial magnetic anisotropy are strongly needed. In this study, we have attempted to fabricate novel, highly anisotropic magnetic materials by employing conventional elements of iron and nickel. An L1_0 type FeNi alloy was successfully fabricated, and various properties of the material were investigated.

  24. ナノグラニュラーシステムを用いたスピン共鳴現象の解明

    Grant number:19656182  2007 - 2008

    萌芽研究

    水口 将輝

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    Authorship:Principal investigator 

    Grant amount:\3300000 ( Direct Cost: \3300000 )

    金属微粒子を絶縁体、あるいは半導体中に分散したグラニュラーシステムに関する様々な研究が古くから行われている。グラニュラー系では興味深い伝導現象が観測されるが、未だ、その伝導機構やスピンダイナミクスに未解明の部分が多い。そこで、本研究では様々な形態のナノサイズグラニュラーシステムにおけるスピンダイナミクスを共鳴現象から明らかにすることを目的とした。本年度は、昨年度得られたグラニュラーシステムの創製方法に関する知見を生かし、微粒子径や微粒子間距離などを様々に変化させたグラニュラー構造を系統的に創製し、共鳴現象を利用したナノサイズグラニュラーシステムの共鳴現象の測定を行い、スピンダイナミクスの解明に着手した。まず、Fe連続膜のFMR測定を行った結果、磁場の印加に従って周波数がシフトする共鳴ピークが観測され、その強度は膜厚の増加に比例することが確認された。続いて、膜厚3nmのFeナノドットを含有するグラニュラー薄膜では共鳴ピークが観測されたのに対し、同膜厚のFe連続膜では明確な共鳴ピークが観測されなかった。蒸着量が等しく構造のみが異なる2種類のFe薄膜において、異なる共鳴現象が観測されたのは非常に興味深い結果である。Feの形状磁気異方性が両者で異なることがその起源として考えられるが、詳細は明らかでない。Feナノ粒子が整列した膜厚0.3nmの試料についても測定を行ったが、明確な共鳴ピークは観測されなかった。これは、Feのスピン数が本手法の検出限界以下であることを示唆している。今後、これを観測するためには、試料をウェーブガイドの中に埋め込むなどの感度を向上させる工夫が必要であると考えられる。

  25. 絶縁体上の超平担表面誘起強磁性層の創成とそのスピン依存伝導特性に関する研究

    Grant number:17760011  2005 - 2006

    水口 将輝

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    Authorship:Principal investigator 

    Grant amount:\3300000 ( Direct Cost: \3300000 )

    絶縁体である酸化マグネシウム基板上に強磁性鉄薄膜および酸化マグネシウム超薄膜を積層成長し、その構造と輸送特性の相関を調べた。薄膜の成長は分子線エピタキシ法を用いて行った。酸化マグネシウム基板上に酸化マグネシウム緩衝層を成長した後、強磁性鉄薄膜(膜厚50ナノメートル)を成長し、続いて酸化マグネシウム超薄膜を成長した。強磁性鉄薄膜および酸化マグネシウム超薄膜のエピタキシャル成長を反射高速電子回折により確認した。製膜後の試料を超高真空のまま走査型トンネル顕微鏡を備えたチャンバに搬送し、その表面構造を観察した。顕微鏡観察はタングステン探針を用い、室温、一定電流モードで行った。走査型トンネル顕微鏡による観察の結果、酸化マグネシウム絶縁膜の膜厚が3原子層から5原子層まで増加するに従い、表面の平坦性が増すことが確認された。また、製膜後の熱処理により、表面平坦性が向上することも確認された。これは、強磁性鉄薄膜/酸化マグネシウム超薄膜/強磁性鉄薄膜の強磁性トンネル接合において、熱処理によりトンネル磁気抵抗比が大きく上昇するという実験事実と一致し、この上昇が熱処理による界面構造の平坦化によるものであることを示唆している。さらに、酸化マグネシウム超薄膜の伝導特性を走査型トンネル分光により調べた結果、膜厚3原子層と5原子層の間に一様バリアが形成される臨海膜厚が存在することが分かった。これらの結果により、超平坦な表面有機強磁性層の創成へのてがかりを得ることができた。

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Media Coverage 1

  1. 熱電変換効率を大幅向上 Newspaper, magazine

    日刊工業新聞  2020.7