Country：Japan

Country：Japan

Country：Japan

Award type：Award from publisher, newspaper, foundation, etc.  Country：Japan

Award type：Award from publisher, newspaper, foundation, etc.  Country：Japan

Award type：Award from publisher, newspaper, foundation, etc.  Country：Japan

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228509

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228793

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1039/d3tc01915b

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1038/s41467-023-39103-2

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1103/physrevapplied.19.064077

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1063/5.0151832

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1063/5.0150917

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1088/1361-648x/accc66

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

We report zero-field routing of spin waves in a multiferroic heterostructure comprising a ferromagnetic Fe film and a ferroelectric BaTiO₃ substrate with fully correlated strain-coupled domains. In the Fe film, a regular alternation of magnetic anisotropy produces a back-and-forth rotation of uniform magnetization in zero magnetic field. Spin waves propagating across this domain structure are refracted at the magnetic domain walls because of abrupt changes in the dispersion relation and phase velocity. Using super-Nyquist sampling magneto-optical Kerr effect microscopy, we image the routing of spin waves and analyze the dependence of the effect on frequency and the propagation direction. We find that spin waves are routed efficiently by angles up to 60° without measurable loss in amplitude. The experimental results are reproduced by micromagnetic simulations and calculations based on the modified Snell's law for magnonics.

DOI： 10.1063/5.0086430

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.105.014417

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.105.014417/fulltext

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/adma.202100646

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/adma.202100646

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Surface Science Society Japan  

DOI： 10.1380/vss.64.230

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0039577

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

© 2019 The Authors LiCoO2 (LCO) is one of the most promising cathode materials for Li ion batteries (LIBs). However, LCO shows a rate-limiting step of Li+ migration between electrode and electrolyte interfaces, requiring LIBs to be charged under low-current conditions. For next generation batteries, it will be necessary to meet the demand for a shorter charging-time. We investigated a support method for the LCO surface to improve high C-rate performance, and revealed that the Li+ intercalation/de-intercalation reaction into/from LCO was accelerated by the introduction of a BaTiO3-LCO-electrolyte interface (triple-phase interface; TPI), due to the electric field concentration near the TPI. In this report, we investigate the dependence of high C-rate performance on the density of surface BaTiO3 nanodots using epitaxial LiCoO2 thin films created via pulsed laser deposition (PLD). As the number of nanodots increased, so did discharge capacity at 50C, becoming saturated at surface coverage over 22%. However, at 100C, the discharge capacity decreased at surface coverage over 40%. These results indicate that coalescence of nanodots reduces not only the TPI length but also the electrochemically active range at quite high C-rate. Therefore, we infer that optimal surface coverage should be varied depending on the C-rate.

DOI： 10.1016/j.elecom.2019.106604

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Language：English   Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. We previously reported that the BaTiO3(BTO)-LiCoO2(LCO)-electrolyte triple-phase interface (TPI) could play an important role in C-rate enhancement, however, why this supporting material is effective for high performance remains unknown. We focus on the relative permittivity of supporting materials using finite element method calculations and experiments. Calculations revealed that the electric field near the TPI was reinforced as the relative permittivity of supporting materials increased. Experimentally, we prepared nanodots and micropads deposited on LCO thin film using BTO and CeO2 as supporting materials to evaluate electrochemical properties and SEI formation mechanisms, respectively. High C-rate performance was improved by the introduction of CeO2 and BTO nanodots; however, only the BTO nanodots deposited on LCO could work at 100C. In addition, SEI around the TPI was quite thin around CeO2 and BTO pads, although 10 and 300 nm SEI were observed at the non-pad area of CeO2 and BTO, respectively. This indicated that the Li+ motion between electrolyte and electrode could be accelerated depending on the relative permittivity of supporting materials. The low SEI around the TPI of both the CeO2 and BTO pads suggested that the main reactions of Li+ insertion/de-insertion into/from LCO might be dominant around the TPI area.

DOI： 10.1016/j.jpowsour.2019.227194

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

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

Controlling magnetic anisotropy by orbital magnetic moments related to interfacial strains has considerable potential for the development of future devices using spins and orbitals. For the fundamental physics, the relationship between strain and orbital magnetic moment is still unknown, because there are few tools to probe changes of orbital magnetic moment. In this study, we developed an electric field (E)-induced X-ray magnetic circular dichroism (EXMCD) technique to apply E to a ferroelectric BaTiO3 substrate. We reversibly tuned the interfacial lattice constants of Ni/Cu multilayers on BaTiO3 using this technique. As the domain structures in BaTiO3 are modulated by E, EXMCD measurements reveal that the changes in the magnetic anisotropy of Ni/Cu films are induced through the modulation of orbital magnetic moments in Ni with magneto-elastic contributions. The strained Ni layer that induces the perpendicular magnetic anisotropy without E is released at E = 8 kV/cm, and in-plane magnetization also occurs. We observed that EXMCD measurements clarified the origin of the reversible changes in perpendicular magnetic anisotropy and established the relationship between macroscopic inverse magnetostriction effects and microscopic orbital moment anisotropy.

DOI： 10.1038/s41535-019-0159-y

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Scopus

Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.nanolett.8b04690

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2109/jcersj2.19048

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Language：English   Publishing type：Research paper (scientific journal)  

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.57.101201

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

We investigated the thermoelectric properties of high-quality p-type Cu2ZnSnS4 single crystals. This material showed two advantages: low thermal conductivity because of lattice scattering caused by the easily formed Cu/Zn disordered structure, and high conductivity because of high doping from changes to the composition. All samples showed a thermal conductivity of 3.0 W m%1 K%1 at 300 K, and the Cu-poor sample showed a conductivity of 7.5 S/cm at 300 K because of the high density of shallow-acceptor Cu vacancies. The figure of merit of the Cu-poor Cu2ZnSnS4 reached 0.2 at 400 K, which is 1.4–45 times higher than those of related compounds.

DOI： 10.7567/APEX.11.051203

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Scopus

Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5006597

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.5020956

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

The uniaxial in-plane magnetic anisotropy constants (K1) of amorphous Co10Fe74B16 (CoFeB) films deposited on BaTiO3 (BTO) single-crystal substrates are characterized using a vibrating sample magnetometer. As a result, a significant increase in K1 with temperature is observed by a factor of 26, from 0.267 × 105 erg cm−3 at 300 K to 6.88 × 105 erg cm−3 at 230 K, and the thermal/K1 cycling was reproduced. Estimation of the magnetoelastic effect at the CoFeB/BTO interface demonstrated that the external stress resulting from the structural phase transition from tetragonal to orthorhombic structure in the (001) plane of BTO substrate is the primary cause of the instant magnetic anisotropy in amorphous systems with isotropic magnetostriction such as CoFeB.

DOI： 10.1002/pssa.201700762

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/APEX.11.013008

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Publishing type：Research paper (scientific journal)  

© Materials Research Society 2018. Lithium ion batteries with high-rate performance have been demanded since electric and hybrid vehicles are released. It is known that high interfacial resistance between electrode and electrolyte prevents intercalation of lithium ions. We investigated high-rate capability of typical LiCoO2 cathode with various surface morphologies using epitaxial thin films prepared by pulsed laser deposition. As a result, high-rate performance in (104)LiCoO2 thin films was enhanced by an increase of (110)LiCoO2 facet density because diffusion coefficient of (110)LiCoO2 was larger than that of (104)LiCoO2. Therefore, a control of crystal plane at the surface is a key point for high-rate performance.

DOI： 10.1557/adv.2018.253

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Thermally driven magnetization switching of perpendicularly magnetized [Cu/Ni] multilayer/BaTiO3(100) heterostructures is demonstrated. While the magnetization of the multilayer shows the out-of-plane magnetic anisotropy in the tetragonal phase of BaTiO3 at room temperature, the magnetization orientation is found to switch from the out-of-plane to the in-plane in the rhombohedral phase below 180 K. The magnetization switching is attributed to the interfacial compressive strain transfer from BaTiO3 to [Cu/Ni] due to the structural phase transitions of BaTiO3. Magneto-optical polar Kerr measurement in the rhombohedral phase with and without applying an electric field supports the description that the magnetization switching arises from the compressive strain at the interface induced by the structural phase transition from the orthorhombic to rhombohedral phases.

DOI： 10.1109/NANO.2017.8117394

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssr.201700294

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DOI： 10.1063/1.4990947

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DOI： 10.1016/j.cap.2017.02.012

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4979267

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Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：電子情報通信学会  

Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：ホログラフィック・研究会  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4964826

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.94.140401

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DOI： 10.1021/acs.cgd.6b00770

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/am.2016.101

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4953464

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4943606

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Language：English   Publishing type：Part of collection (book)   Publisher：wiley  

This chapter reviews some recent developments in electron spin conversion technology. The mechanism of the conversion of electron spin into the photon helicity in GaAs is briefly described according to the optical transition selection rules in the radiative electron-hole recombination process. This is followed by a discussion on recent experimental results of spin injection into GaAs across a Fe3O4 spin filter. Optical spin orientation method, which coverts the photo helicity into the electron spin, is also described to examine the spin-filtering effect at a Fe/AlGaAs interface, the efficiency of which can be optimized by electric voltage across the interface. The effect of injecting spin-polarized electrons into a chemically ordered FeRh alloy which shows the antiferromagnetic-ferromagnetic phase transition is presented in order to see how spin-polarized electrons influence the magnetic phase transition. The chapter concludes with the future prospect of spintronics technology.

DOI： 10.1002/9781118751886.ch8

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0953-8984/27/50/504001

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4931567

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.92.094416

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4929695

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DOI： 10.1063/1.4929339

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2015.04.012

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/am.2015.72

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.54.073002

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevB.91.214425

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevX.5.011010

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DOI： 10.1016/j.phpro.2015.12.153

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DOI： 10.1063/1.4900619

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4900619

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jcrysgro.2013.11.077

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DOI： 10.1063/1.4871208

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DOI： 10.1063/1.4866798

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DOI： 10.1063/1.4862969

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DOI： 10.1016/j.jcrysgro.2013.10.001

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DOI： 10.1063/1.4861455

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Japan Society of Powder and Powder Metallurgy  

The 11th International Conference on Ferrites, ICF11, was successfully held on April 15-19, 2013, at the Okinawa Convention Center, Okinawa, Japan organized by The Japan Society of Powder and Powder Metallurgy. ICF 11 covered a broad range of topics related to the science and technology of ferrites and related materials.

DOI： 10.2497/jjspm.61.S5

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4821279

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DOI： 10.1002/pssa.201200815

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DOI： 10.1063/1.4795819

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DOI： 10.1063/1.4793511

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0953-8984/25/13/132001

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DOI： 10.7566/JPSJ.82.033706

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DOI： 10.1038/am.2012.72

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DOI： 10.7567/APEX.6.015803

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DOI： 10.1063/1.4773482

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DOI： 10.1080/00150193.2012.743786

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1541/ieejfms.132.920

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DOI： 10.1016/j.jcrysgro.2012.05.030

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DOI： 10.1063/1.3693524

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DOI： 10.1063/1.3693524

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DOI： 10.1016/j.jcrysgro.2011.12.046

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DOI： 10.1016/j.jcrysgro.2011.12.046

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.3684695

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DOI： 10.4028/www.scientific.net/MSF.725.171

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DOI： 10.1143/JJAP.50.128001

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DOI： 10.1117/12.892386

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.107.146801

Scopus

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DOI： 10.1063/1.3628464

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DOI： 10.1063/1.3609237

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DOI： 10.1063/1.3609234

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DOI： 10.1038/asiamat.2011.84

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DOI： 10.1143/JJAP.50.05FB04

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DOI： 10.1063/1.3536668

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DOI： 10.1063/1.3556754

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DOI： 10.1063/1.3553941

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JPSJ.80.033701

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DOI： 10.1088/0953-8984/23/7/075901

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DOI： 10.1063/1.3518919

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DOI： 10.1063/1.3509419

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.105.156601

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DOI： 10.1143/JPSJ.79.043706

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DOI： 10.1063/1.3357436

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DOI： 10.1103/PhysRevB.81.085317

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DOI： 10.1080/00150191003751422

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevLett.102.236806

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.3379/msjmag.0903RD8093

J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.3054386

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DOI： 10.1063/1.3054357

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

For the study of ferromagnetic materials which are compatible with group-IV semiconductor spintronics, we demonstrate control of the ferromagnetic properties of Heusler-alloy Fe3-xMnxSi epitaxially grown on Ge(111) by tuning the Mn composition x. Interestingly, we obtain L2(1)-ordered structures even for nonstoichiometric atomic compositions. The Curie temperature of the epilayers with x approximate to 0.6 exceeds 300 K. Theoretical calculations indicate that the electronic structures of the nonstoichiometric Fe3-xMnxSi alloys become half-metallic for 0.75 <= x <= 1.5. We discuss the possibility of room-temperature ferromagnetic Fe3-xMnxSi/Ge epilayers with high spin polarization.

DOI： 10.1103/PhysRevLett.102.137204

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 10.1088/1742-6596/193/1/012046

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

DOI： 10.1002/asia.200900235

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We report the results of thermodynamic measurements on the quasi one-dimensional (1D) Ising-like antiferromagnet BaCo2V2O8 in the magnetic fields for H//c down to 200 mK. An appearance of a long range magnetic ordered phase is observed in the field induced region above H-c similar or equal to 3.9 T at temperature below 1.8 K. A peculiar incommensurate ordering, which reflects a quantum critical nature of S = 1/2 1D Ising-like antiferromagnet, realizes in this ordered phase.

DOI： 10.1088/1742-6596/150/4/042090

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J-GLOBAL

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

We demonstrate the tunneling magnetoresistance (TMR) effect through a semiconductor quantum dot (QD) with a few electrons in a lateral QD spin-valve device. At one-to-two electron transition, only inverse TMR effect is observed, where the TMR ratio is relatively large compared with the value based on the Julliere model. When the bias window reaches near the charging energy of the QD, the inverse TMR almost disappears. These features can be interpreted in terms of spin transport via the ground state of a two-electron QD.

DOI： 10.1063/1.3042098

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

From neutron diffraction measurements on a quasi-1D Ising-like Co2+ spin compound BaCo2V2O8, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the Neel-type ordering, which is expected for the classical system, and the peculiar spin structure is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering.

DOI： 10.1103/PhysRevLett.101.207201

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/cm801905d

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Other Link： http://orcid.org/0000-0003-3683-5416

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

The rapid rise of spintronics and quantum information science has led to a strong interest in developing the ability to coherently manipulate electron spins(1). Electron spin resonance(2) is a powerful technique for manipulating spins that is commonly achieved by applying an oscillating magnetic field. However, the technique has proven very challenging when addressing individual spins(3-5). In contrast, by mixing the spin and charge degrees of freedom in a controlled way through engineered non-uniform magnetic fields, electron spin can be manipulated electrically without the need of high-frequency magnetic fields(6,7). Here we report experiments in which electrically driven addressable spin rotations on two individual electrons were realized by integrating a micrometre-size ferromagnet into a double-quantum-dot device. We find that it is the stray magnetic field of the micromagnet that enables the electrical control and spin selectivity. The results suggest that our approach can be tailored to multidot architecture and therefore could open an avenue towards manipulating electron spins electrically in a scalable way.

DOI： 10.1038/nphys1053

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Other Link： http://orcid.org/0000-0003-3683-5416

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

Magnetic behaviors of the magnetic semiconductor Mn-doped AgGaSe(2) with no secondary phases are reported. Magnetization measurements show that Mn-doped AgGaSe(2) exhibits a superparamagnetic behavior while undoped AgGaSe(2) shows diamagnetism. Significant anomalies are also seen in the temperature dependent ac susceptibility and specific heat at 190 and 275 K. These results indicate that the substitution of Mn induces magnetism in AgGaSe(2). The origin of the magnetic behaviors is discussed on the basis of the combined results of susceptibility, specific heat, and photoluminescence.

DOI： 10.1063/1.2831500

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J-GLOBAL

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

We demonstrate fully epitaxial growth of Fe(3)O(4)/GaAs(001) heterostructures using a reactive molecular beam epitaxy (MBE) method. The Fe(3)O(4) film was obtained by oxidizing an ultrathin Fe layer into an Fe(3)O(4) seed layer in an O(2) atmosphere at 260 degrees C, followed by the reactive MBE growth of Fe(3)O(4). The Fe(3)O(4) seed layer effectively works as a template for the successive growth of Fe(3)O(4). Also, a clear spin filtering effect of optically spin oriented electrons at the Fe(3)O(4)/GaAs(001) interface is shown at room temperature. The results clearly demonstrate that the spin filtering effect occurs at the Fe(3)O(4)/GaAs(001) interface and has its origin in the spin split density of states of the Fe(3)O(4) layer. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2832415

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A clear correlation between the spin filtering effect of optically pumped spin-polarized electrons at Fe/GaAs(001) Schottky interfaces and its electron transmission mechanism is reported. Current-voltage (I-V) characteristics of the Schottky diode demonstrate tunneling and thermionic emission transmission processes in the low and high bias voltage regions, respectively. A spin filtering current contribution, on the other hand, exhibits a significant peak at a particular bias voltage while spin selectivity shows a shoulder at the same bias voltage. The bias voltage where the features occur corresponds well to the crossover regime of the electron transmission mechanisms. The spin selectivity also shows a field dependence similar to the magnetization curve, assuring that the spin selectivity has its origin in the spin filtering effect. (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2829904

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We report the growth and the piezoelectric properties of lead-free perovskite single crystals of Ag1-xLixNbO3. It possesses a rhombohedral structure with high ferroelectric phase transition (T-c=548 K for x=0.086) and large spontaneous polarization (P-s similar to 40 mu C/cm(2) for x=0.062) along the < 111 >(c) direction of pseudocubic perovskite structure for x>0.05-0.06. High quasistatic d(33)similar to 210 pC/N and low dielectric constant have lead to a very large value of piezoelectric voltage constant g(33)similar to 53.9x10(-3) Vm/N for the < 001 >(c)-cut crystal of this simple perovskite. It has been shown that Li substitution might enhance the piezoelectric coefficient of the crystal. The excellent piezo-/ferroelectricity of this system are considered to be facilitated by the strong polarization nature of both Ag and Li in the perovskite structure. Our findings may stimulate further interests in the development of lead-free piezoelectrics. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2918837

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

Martensite transformation temperature of ferromagnetic shape memory alloy FePd was studied in the shape of nanoparticle and the polycrystalline samples with grain size in micrometers based on the x- ray diffraction and magnetic measurement as a function of sample size. Both the forward transformation start temperature M(s) and reverse transformation finish temperature A(f) of polycrystalline sample monotonically decreased with decreasing grain size and were not observed in the nanoparticles. The size dependence of transformation temperature is explained based on the change in transformation mode, i. e., the decrease in sample size induces the change from the multivariant mode to single variant mode in which the strain energy is large. In the small sample, the strain energy becomes large, and thus the large driving force is required for the transformation. As a result, the large amount of undercooling occurs, which leads to the lowering of Ms. The measurement of heat capacity indicates that the strain energy is elastically stored without dispersion in the transformation process even in the small size because the volume change of FePd at the transformation is very small. The large elastic strain energy works as the driving force to reverse transformation, and then the lowering of Af is induced. Therefore, the lowering of transformation temperature in FePd is characterized by the lowering of thermodynamic equilibrium temperature. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2890143

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Local probing of conduction behaviors using atomic force microscopy clearly shows that the grain boundary of polycrystalline CaCu3Ti4O12 is Semiconducting. In contrast, the grain is a mixture of semiconductinc, and insulating regions. This inhomogeneous conductive feature leads to giant dielectric response in CaCu3Ti4O12. Theoretical analysis demonstrates that the dielectric response follows a typical Debye-type relaxation, and its unusual temperature dependence originates from the thermal activation behavior of free carries within the semiconducting regions in the grain. An effective way to control the electrical properties of CCTO is to control the defect density within a grain rather than the grain boundary.

DOI： 10.1021/cm0710507

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We report the observation of room temperature ferromagnetism in high quality, single crystalline dilute Fe-doped BaTiO3. The large equilibrium solubility of Fe ions in the matrix refutes uncertainties about secondary phase magnetism, which has often eclipsed this interesting field of research. While room temperature ferromagnetism is observed at and above 5% Fe concentrations, one finds a highly concave temperature dependence of the susceptibility. Using detailed ab initio calculation, this has been related to intrinsic magnetic inhomogeneities arising from positional disorder. Apart from providing a mechanism for the observed high temperature ferromagnetism, our results point out that intrinsic disorder is a generic and essential component of dilute magnetism.

DOI： 10.1103/PhysRevB.77.104416

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Mn-doped ZnO films on Si substrate could be grown by the spray pyrolysis method at 500 degrees C under an air atmosphere. Although the orientation (0 0 0 2) peak intensity became small with increasing Mn concentration, the lattice constant of the c-axis expanded monotonously with increasing Mn concentration. This indicated that the Mn ion was understood to have occupied the Zn site without changing wurtzite structure. Furthermore, the magnetic signal which increased with decreasing temperature was presumably due to superparamagnetic clusters in the ZnO film because (chi - chi(0))(-1), chi and chi(0) represented the susceptibility and the temperature-independent paramagnetic contribution from the substrate, respectively, could be well fitted with the Curie law, giving almost zero Curie temperature. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2007.09.074

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

High-field specific heat measurements on BaCo2V2O8, which is a good realization of an S=1/2 quasi-one-dimensional (1D) Ising-like antifferomagnet, have been performed in magnetic fields up to 12 T along the chain and at temperature down to 200 mK. We have found a new magnetic ordered state in the field-induced phase above H-c similar or equal to 3.9 T. We suggest that a novel type of the incommensurate order, which is caused by the quantum effect inherent in the S = 1/2 quasi-1D Ising-like antiferromagnet, appears in the field-induced phase.

DOI： 10.1103/PhysRevLett.100.057202

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We experimentally study the tunneling magnetoresistance (TMR) effect as a function of bias voltage (V-SD) in lateral Ni/InAs/Ni quantum-dot (QD) spin valves showing Coulomb blockade characteristics. With varying V-SD, the TMR value oscillates and the oscillation period corresponds to conductance changes observed in the current-voltage (I-V-SD) characteristics. We also find an inverse TMR effect near V-SD values where negative differential conductance is observed. A possible mechanism of the TMR oscillation is discussed in terms of spin accumulation on the QD and spin-dependent transport properties via excited states.

DOI： 10.1103/PhysRevB.77.081302

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Using a laterally fabricated quantum-dot (QD) spin-valve device, we experimentally study the Kondo effect in the electron transport through a semiconductor QD with an odd number of electrons (N). In a parallel magnetic configuration of the ferromagnetic electrodes, the Kondo resonance at N=3 splits clearly without external magnetic fields. With applying magnetic fields (B), the splitting is gradually reduced, and then the Kondo effect is almost restored at B=1.2 T. This means that, in the Kondo regime, an inverse effective magnetic field of B similar to 1.2 T can be applied to the QD in the parallel magnetic configuration of the ferromagnetic electrodes. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2820445

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

High field magnetization and ESR measurements on the quasi-one-dimensional (1D) antiferromagnet BaCo2V2O8 have been performed in magnetic fields up to 50 T along the chain. The experimental results are explained well in terms of a 1D S=1/2 antiferromagnetic XXZ model in longitudinal fields. We show that the quantum phase transition from the Neel ordered phase to the spin liquid one in the model is responsible for a peculiar order to disorder transition in BaCo2V2O8.

DOI： 10.1103/PhysRevLett.99.087602

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The authors demonstrate an electric-field control of tunneling magnetoresistance (TMR) effect in a semiconductor quantum-dot spin-valve device. By using ferromagnetic Ni nanogap electrodes, they observe the Coulomb blockade oscillations at a small bias voltage. In the vicinity of the Coulomb blockade peak, the TMR effect is significantly modulated and even its sign is switched by changing the gate voltage, where the sign of the TMR value changes at the resonant condition. (C) 2007 American Institute of Physics.

DOI： 10.1063/1.2759264

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Large single crystals of the novel vanadate Co3V2O8 are grown at a slow cooling rate using the flux method. X-ray diffraction and chemical analyses show that the grown crystals have high quality. Magnetic susceptibility and heat capacity measurements confirm that Co3V2O8 exhibits unusual magnetic behaviors, where five magnetic phase transitions occur below 15 K along the magnetic easy a-axis.

DOI： 10.1021/cg060539u

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Polarization measurements reveal that AgNbO3 has an extremely large polarization, which can reach a value of 52 mu C/cm(2) in polycrystals. Experiments also show that the large internal atom distortion in AgNbO3 is also strongly coupled to the electric field, indicating that high piezoelectric performance can be realized in AgNbO3 system. This finding opens the way to designing a new class of lead-free, high-performance piezoelectric materials based on AgNbO3. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2751136

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

We report on electrical bias voltage manipulation of the magnetic domain structures of patterned ferromagnetic Fe dots on a ferroelectric BaTiO(3) underlayer using a scanning probe microscope technique. Piezoresponse force microscopy is used to apply local electric field on the Fe dots/BaTiO(3) hybrid structure and to map the ferroelectric domain structures simultaneously. Magnetic force microscope observation also demonstrates that the magnetic domain structures of the Fe dots significantly change with the application of voltage at room temperature through the coupling between piezoelectric and magnetostrictive effects, indicating that the Fe dots/BaTiO(3) hybrid structure provides a promising basis for controlling micromagnetic domain structures using electric voltage.

DOI： 10.1063/1.2711280

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Evidence for ferromagnetism at the surface of a LaCoO3 single crystal is reported using a scanning superconducting quantum interference device (SQUID) microscope. Stray magnetic flux detected with the scanning SQUID shows typical ferromagnetic behavior in LaCoO3 below T-c similar to 85 K, in agreement with previous work on LaCoO3 particles. Analysis of the magnetization of LaCoO3 particle samples clearly shows that the magnetization is inversely proportional to the particle radius, giving the information that the ferromagnetism is restricted within a few unit cell layers from the surface. X-ray photoemission spectroscopy also indicates that the ferromagnetism likely originates from the metallic surface due to hole doping with oxygen chemisorption.

DOI： 10.1103/PhysRevB.75.184426

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Spin glass particles were prepared as the mesoscopic system in order to examine the space scale of spin glass domain (droplet). The peak temperature T-peak in the temperature-dependent magnetization is systematically reduced with decreasing average particle size. This is due to the imitation of droplet growth to the particle diameter. The magnetic field H also decreases T-peak, which is caused by the reduction of the barrier height by Zeeman energy. However, there appears different tendency in the relation between H and T-peak below 100 Oe. This indicates the existence of crossover between the two regimes in which the free energy and Zeeman energy govern the droplet excitation. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.640

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Magnetic properties of SrCo2V2O8 single crystal are investigated by means of ac magnetic susceptibility, dc magnetization and heat capacity measurements. The results show that SrCo2V2O8 possesses two canted antiferromagnetic transitions at similar to 5 and similar to 3 K, which is different from isostructural BaCo2V2O8 with only one anti ferromagnetic transition at similar to 5 K. We suggest that such different magnetic properties are mainly due to their different structural symmetry. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2007.01.010

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Linear and nonlinear magnetic susceptibilities of a LaCoO3 particle sample were measured to shed light on the surface ferromagnetism of LaCoO3. The ferromagnetic transition temperature T-C estimated from the nonlinear magnetic susceptibility agrees well with that inferred from Kouvel-Fisher's analysis of the linear susceptibility, while the critical exponent gamma deduced simultaneously from the same analysis is incompatible with any values reported for 2d and 3d ferromagnetism. The results are discussed in view of surface and/or size effects in detail. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.11.117

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The measurement of spin glass in zero magnetic field is essential to investigate the intrinsic nature of spin glass. We pay attention to tunnel resistance between spin-glass layers. The temperature dependence of tunnel resistance between spin-glass layers with the structure of AgMn/Al2O3/AgMn was measured, and was compared with that of Al/Al2O3/AgMn. For the junction of AgMn/Al2O3/AgMn, tunnel resistance shows a peak around the spin-glass transition temperature, but no peak was observed for the junction of Al/Al2O3/AgMn. The results indicate that the magnetic correlation between spin-glass layers is reflected to tunnel resistance. The singularity of the tunnel resistance between spin-glass layers is discussed by the droplet theory. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.1099

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The authors have fabricated a lateral double barrier magnetic tunnel junction (MTJ) which consists of a single self-assembled InAs quantum dot (QD) with ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance (TMR) effect, which is evidence for spin transport through a single semiconductor QD. The TMR ratio and the curve shapes are varied by changing the gate voltage.

DOI： 10.1063/1.2435957

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Dense polycrystalline samples of CaCu3Ti4O12 (CCTO) were prepared by solid-state reaction method under a high hydraulic pressure of 700 MPa, and characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy (AFM). Probing of the conduction path in nanoscale by AFM reveals that the grain boundary layer is conductive in CCTO. Therefore, reported giant-dielectric response in CCTOcan not be understood by the model of conducting grains surrounded by insulating grain boundaries, which is usually used for the explanation of conventional internal barrier layer capacitors.

DOI： 10.1080/00150190601187500

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Magnetic properties of peculiar structural-type borate Cu2NiB2O6 are investigated by means of ac susceptibility, dc magnetization, and heat capacity measurements. This material is isostructural to Cu2CoB2O6, of which the structural configuration is composed of quasi-one-dimensional six-columns ribbons. Our experimental results show that this material displays an antiferromagnetic phase transition at similar to 15 K. which differs from Cu2CoB2O6 showing spin-glass behavior below 5 K. The different magnetic ground states in these compounds may be attributed mainly to the subtle balance of the exchange energy in the scalene triangles. (c) 2006 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2006.08.034

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Magnetic properties of BaCu2V2O8 single crystals obtained by the spontaneous nucleation method using V2O5 as a self-flux are investigated. Singlet ground states with spin gaps of 215 and 223 K are observed along the directions parallel and perpendicular to the c-axis of the crystal, respectively, being in good agreement with powder sample measurements. Reinvestigation of the crystal structure reveals that the whole structural framework of BaCu2V2O8 crystal can be described as an assembly of alternating chains, which are built by edge-sharing pairs of CuO4 square-plaquettes and VO4 tetrahedra along the c-axis. The magnetic nature of BaCu2V2O8 is well understood based on this structural interpretation. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.03.041

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We report on the growth condition and magnetic properties of SrCo2V2O8 crystal. High-quality single crystals with dimensions 3x3x6 mm(3) have been successfully grown from its stoichiometrical melt in air by spontaneous nucleation method. Preliminary magnetic measurements show large canted ferromagnetism and unusual paramagnetic anisotropy of the grown crystals. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2006.05.039

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We study a possible mechanism of the switching of the magnetic easy axis as a function of hole concentration in (Ga,Mn)As epilayers. In-plane uniaxial magnetic anisotropy along [110] is found to exceed intrinsic cubic magnetocrystalline anisotropy above a hole concentration of p=1.5x10(21) cm(-3) at 4 K. This anisotropy switching can be realized by postgrowth annealing, and the temperature-dependent ac susceptibility is significantly changed with increasing annealing time. On the basis of our recent scenario [Phys. Rev. Lett. 94, 147203 (2005) and Phys. Rev. B 73, 155204 (2006)], we deduce that the growth of highly hole-concentrated cluster regions with [110] uniaxial anisotropy is likely the predominant cause of the enhancement in [110] uniaxial anisotropy at the high hole concentration regime. We can clearly rule out anisotropic lattice strain as a possible origin of the switching of the magnetic anisotropy.

DOI： 10.1103/PhysRevB.74.045201

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We study the effect of the shape anisotropy on the magnetic domain configurations of a ferromagnetic semiconductor (Ga,Mn)As/GaAs(001) epitaxial wire as a function of temperature. Using magnetoresistance measurements, we deduce the magnetic configurations and estimate the relative strength of the shape anisotropy compared with the intrinsic anisotropies. Since the intrinsic anisotropy is found to show a stronger temperature dependence than the shape anisotropy, the effect of the shape anisotropy on the magnetic domain configuration is relatively enhanced with increasing temperature. This information about the shape anisotropy provides a practical means of designing nanostructured spin electronic devices using (Ga,Mn)As. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2196113

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Magnetic and heat capacity studies of the 1D anisotropic antiferromagnet SrCo2V2O8 demonstrate field-induced magnetic transitions in longitudinal and transverse magnetic fields. An antiferromagnetic (AF)-paramagnetic (PM) transition is observed instead of spin-flop transition in longitudinal magnetic field parallel to the magnetic easy c-axis. The temperature-field (T-H) phase diagram clearly shows that the AF-PM transition occurs in the same framework for both longitudinal and transverse magnetic fields in SrCo2V2O8. This is an experimental observation of such magnetic behaviors in an anisotropic antiferromagnet, irrespective of the field directions.

DOI： 10.1103/PhysRevB.73.212406

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DOI： 10.1063/1.2194121

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

The order parameter S of Fe-Pt nanoparticles is estimated from X-ray diffraction (XRD) patterns. The total intensity of a diffraction peak is obtained by Rietveld analysis as well as simply integrating the intensity. The Rietveld analysis is found to provide a plausible value of S even for a sample showing an XRD pattern with broad and overlapped peaks. Another order parameter Q, which is obtained from Mossbauer spectra, is introduced, and it is confirmed that Q is equivalent to the probability of Fe atoms being in the L1(0)-type atomic arrangement. The coercivity of Fe-Pt nanoparticles is directly proportional to Q, while it vanishes at S = 0.4, indicating that the magnetic property of Fe-Pt nanoparticles has a closer relationship to Q than S. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2005.05.016

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We report the temperature dependence of the resistivity, magnetic susceptibility, and heat capacity of single crystalline Pb2Ru2O6.5 and Bi2Ru2O7, the metallic members of the pyrochlore ruthenates. The analysis of the T-2 coefficient of the resistivity, Pauli paramagnetic susceptibility, and linear heat-capacity coefficient indicates that Pb2Ru2O6.5 is a well-defined Fermi liquid with strong electron correlation. For Bi2Ru2O7, thermodynamic data suggest moderately correlated behavior, while the resistivity shows unusual behavior that can be attributed to the structural disorder in this compound. A comparison with the insulating pyrochlore ruthenates underlines the critical role of easily polarizable Pb/Bi ions in inducing the metallic properties and structural modifications observed in these compounds.

DOI： 10.1103/PhysRevB.73.193107

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Spin-selective transport of optically pumped spin-polarized electrons across 5-nm-thick Fe wires/GaAs and 5-nm-thick Fe wires/AlOx(1.5 nm)/GaAs interfaces is studied as functions of magnetic field and temperature. We find characteristic temperature dependence of the spin selectivity at the Fe/AlOx/p-GaAs interface, where the selectivity shows a maximum at 200 K, which we attribute to the tunneling effect of spin-polarized electrons across the AlOx layer in the Fe/AlOx/p-GaAs structure. (C) 2006 American Institute of Physics.

DOI： 10.1063/1.2167071

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We report on the growth behavior and surface feature of quasi-one-dimensional anisotropic antiferromagnet BaCo2V2O8 crystal grown from its stoichiometrical melt in air by spontaneous nucleation method. The grown crystals are found to have a characteristic morphology with clear facets, growth lines and veins. Clear steps on the crystal surface show layer-by-layer growth process from a nucleus at the center. Also large defect (vacancies) are clearly seen on the step edges. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jerysgro.2005.11.113

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A scenario of the mechanism of intriguing ferromagnetic properties in Mn-doped magnetic semiconductor (Ga,Mn)As is examined in detail. We find that magnetic features seen in zero-field-cooled and field-cooled magnetizations are not interpreted with a single domain model [Phys. Rev. Lett. 95, 217204 (2005)], and the magnetic relaxation, which is similar to that seen in magnetic particles and granular systems, is becoming significant at temperatures above the lower-temperature peak in the temperature dependence of ac susceptibility, supporting the cluster/matrix model reported in our previous work [Phys. Rev. Lett. 94, 147203 (2005)]. Cole-Cole analysis reveals that magnetic interactions between such (Ga,Mn)As clusters are significant at temperatures below the higher-temperature peak in the temperature dependent ac susceptibility. The magnetizations of these films disappear above the temperature showing the higher-temperature peak, which is generally referred to as the Curie temperature. However, we suggest that these combined results are evidence that the temperature is actually the blocking temperature of (Ga,Mn)As clusters with a relatively high hole concentration compared to the (Ga,Mn)As matrix.

DOI： 10.1103/PhysRevB.73.155204

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Magnetic anisotropy in the one-dimensional spin chain system BaCo2V2O8 is investigated using magnetic susceptibility, magnetization, and heat capacity measurements. Unusual magnetic anisotropy is observed in the paramagnetic state at room temperature. The magnetic anisotropy energy of BaCo2V2O8 is estimated to be greater than 1.44(4)x10(7) erg/cm(3) at 2 K using a simple uniaxial two-sublattice mean-field model. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2189913

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DOI： 10.1088/1/1742-6596/51/1/021

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/3-540-27164-3_4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Order-disorder transition is observed in the quasi-one-dimensional anisotropic spin chain antiferromagnet BaCo2V2O8 in magnetic fields along the magnetic easy c axis below the Néel temperature. We construct the phase diagram in the H-T plane through magnetic and heat capacity measurements and find that the phase boundary of the order-disorder transition can be described in terms of a mean-field power law. We also suggest that quantum critical behavior from three-dimensional Néel ordering back into a one-dimensional disordered phase is observed in magnetic fields above a critical value of 4.4T. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.172403

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Magnetotransport features of a ferromagnetic semiconductor (Ga,Mn)As epilayer are found to change by annealing at 250 degrees C. Magnetoresistance curves of the annealed sample indicate that the change in the magnetic easy axis in the film plane as well as the change in the magnetization reversal processes are induced by the enhancement in the contribution of [110] uniaxial anisotropy. The origin of the enhancement in [110] uniaxial anisotropy is also discussed. (C) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2005.04.059

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The magnetic and magnetotransport properties of very thin as-grown (Ga,Mn)As epilayers are reported. A 10-nm-thick epilayer shows a marked decrease in the Curie temperature and conductivity. The magnetoresistance (MR) increases with decreasing temperature in the temperature range below 20 K and the MR hysteresis curves show a characteristic feature which is different from that of thicker epilayers. We attribute the characteristic feature to the localization of hole carriers at the surface region of the epilayer. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.1844731

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We report on the magnetic and magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As modified by Ga+ ion irradiation using focused ion beam. A marked reduction in the conductivity and the Curie temperature is induced after the irradiation. Furthermore, an enhanced negative magnetoresistance and a change in the magnetization reversal process are also demonstrated at 4 K. Raman-scattering spectra indicate a decrease in the concentration of hole carriers after the irradiation, and a possible origin of the change in the magnetic properties is discussed. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.1844751

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Two different ferromagnetic-paramagnetic transitions are detected in (Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition at a higher temperature results from (Ga,Mn)As cluster phases with [110] uniaxial anisotropy and that at a lower temperature is associated with a ferromagnetic (Ga,Mn)As matrix with &lt; 100 &gt; cubic anisotropy. A change in the magnetic easy axis from [100] to [110] with increasing temperature can be explained by the reduced contribution of &lt; 100 &gt; cubic anisotropy to the magnetic properties above the transition temperature of the (Ga,Mn)As matrix.

DOI： 10.1103/PhysRevLett.94.147203

Web of Science

Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

X-ray magnetic circular dichroism (XMCD) of Pd97.1Fe2.9 fine particle samples is studied at the Pd L-2.3 edges. The magnetic moment of a Pd atom, which is estimated using the magneto-optical sum rule, is similar to 0.06 mu(B)/atom independent of particle size, while the total magnetization of the particle samples decreases monotonically with decreasing particle size. We attribute the size dependent magnetization to a reduction in the Fe magnetic moment at the surface region with decreasing particle size. Analysis of the XMCD data is reported in detail.

DOI： 10.1143/JPSJ.74.1044

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J-GLOBAL

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

Spin selective electron transport across a submicron Fe wire/GaAs(001) interface is studied under optical spin orientation. A significant bias dependence of the difference between photocurrents for two different single domain structures with opposite magnetic orientations is observed at room temperature, which we attribute to the spin selective transport effect of spin polarized electrons excited in GaAs across the interface. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2004.09.047

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

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

Ni/yttria-stabilized zirconia (YSZ) anodes with a multi-layered structure are prepared on YSZ substrates by a low temperature process using electron-beam evaporation method. The Ni/YSZ anode is obtained by reducing a NiO/YSZ anode, and both Ni and YSZ layers have no impurity phases. Scanning ion microscopy (SIM) observation of the cross-section of the anode shows a well-separated structure without Ni diffusion and agglomeration. Tight adhesion between the Ni and YSZ layers is realized by the low temperature process at 800degreesC. The current-voltage and current-power characteristics for three separate single cell samples with the multi-layered anode are measured. The maximum power densities of the single cells using an YSZ as an electrolyte (0.5 rum thick) with a four-layered anode, a six-layered anode, and a 10-layered anode are obtained to be 0.14, 0.12, and 0.32 W/cm(2) at 800degreesC, respectively. The improvement in the performance of the 10-layered anode compared with the four-layered and six-layered anodes is mainly due to an increase in the length of triple phase boundary in the structure and enhancement in the diffusivity of fuel gas. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2004.03.075

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL INST MATERIALS SCIENCE  

The preparation process and proton transport properties of zirconium tricarboxybutylphosphonate Zr(O3PC(CH2)(3)(COOH)(3))(2)(Zr(PBTC))/polybenzimidazole (PBI) composite membranes have been investigated with a view to developing a novel electrolyte for direct methanol fuel cells. A compacted Zr(PBTC) powder sample and a Zr(PBTC)/PBI composite membrane with 50 wt.% Zr(PBTC) content show conductivities of 6.74 x 10(-2) S cm(-1) and 3.82 x 10(-3) S cm(-1) at 200 degreesC under a fully humid condition, respectively. Postsulfonation thermal treatment, which has a great effect on the ligand structure of PBI, gives a marked increase in the conductivity of the membrane by a factor of 2 in the same condition. This effect is mainly attributed to the proton transport via sulfonic acid groups bonded to the PBI unit. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.stam.2004.02.005

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We find significant changes in the in-plane magnetic anisotropy of a (Ga,Mn)As epilayer by low-temperature annealing. Detailed magnetization and transport measurements reveal an enhancement in the contribution of a uniaxial anisotropy along [110] after annealing. The change in the magnetic anisotropy is affected by increasing hole concentration due to the annealing.

DOI： 10.1143/JJAP.43.L904

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The in-plane anisotropic magnetotransport feature of 2-mum-wide (Ga,Mn)As wires is examined at 4 K. The magnetoresistance (MR) features as a function of applied field orientation show clear anisotropy associated with the cubic magnetocrystalline anisotropy. Moreover, the field orientation dependence of the magnetization switching field shows two asymmetric peaks along [110] and [(1) over bar 10], indicating the presence of uniaxial anisotropy along [110]. A simple model incorporating the cubic and uniaxial anisotropies well explains these asymmetric peaks based on magnetization reversal processes via 90degrees domain wall displacement.

DOI： 10.1109/TMAG.2004.832667

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J-GLOBAL

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

The anisotropy field distribution of various Fe-Pt nanoparticle samples with a partially ordered structure is investigated up to 90 kOe using the Flanders and Shtrikman's method. The distribution of the Fe-Pt samples with a low order parameter of 0.66 or a nonequiatomic composition of Fe58Pt42 or Fe41Pt59 is broader than that of the Fe-Pt sample with an almost full order parameter of 0.96 at 5 K. The broad distribution is attributed to an inhomogeneous atomic arrangement with L1(0), L1(2), and disordered structures. The distribution measured at 300 K, on the other hand, is quite different from that at 5 K, indicating a significant thermal effect on the magnetization reversal. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1669352

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J-GLOBAL

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

The surface gas adsorption effect on the magnetic properties of Pd fine particles was studied to elucidate the magnetic structure. The O-2 gas exposure decreases the saturation component of magnetization to similar to 8% of that of a particle with clean surface, but the high field susceptibility was slightly increased. This indicates that the ferromagnetism of the Pd. ne particle is very sensitive to the surface condition and the ferromagnetic ordering exists in the surface region of the. ne particle. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.391

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)  

Scopus

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

The anisotropic magnetotransport properties of a (Ga,Mn)As epilayer and the magnetization switching are studied as a function of temperature. The magnetization switching field shows asymmetry for crystallographically equivalent [110] and [(1) over bar 10] directions at 4 K, and the asymmetry is more significant at 40 K. The magnetization switching features clearly show that cubic magnetocrystalline anisotropy along &lt;100&gt;, which is biased by a small uniaxial anisotropy along the [110] easy axis, is dominant at 4 K. On the other hand, the [110] uniaxial anisotropy competes with the cubic anisotropy and dominates the magnetization switching at 40 K. Accordingly, the magnetization reversal in the (Ga,Mn)As epilayer occurs via 90degrees and 180degrees domain-wall displacement at 4 and 40 K, respectively. A mechanism of the change in the magnetic anisotropy is discussed within a theoretical description of the hole band structure. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1629134

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Scopus

J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We report clear evidence of the ferromagnetism of gas-evaporated Pd fine particles with a clean surface. The clean Pd particle is found to have a magnetic heterostructure: the surface of the particle is ferromagnetic and the rest is paramagnetic. The size dependence of the magnetic saturation component reveals that the ferromagnetic ordering occurs only on (100) facets of the particle and that the topmost two to five layers from the surface contribute to the ferromagnetism with a magnetic moment of (0.75+/-0.31)mu(B)/atom.

DOI： 10.1103/PhysRevLett.91.197201

Web of Science

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

Recent advances in spin-polarized electron transport at the ferromagnet/semiconductor interface are summarized in the context of potential applications to spin-electronics. We review evidence for spin injection from a ferromagnetic metal into a semiconductor based on recent studies of polarized luminescence in ferromagnet/quantum well light emitting diode structures. Our recent results on spin-polarized electron transport from GaAs into Fe under optical spin pumping are shown. These observations clearly indicate an importance of the introduction of a tunneling barrier between the ferromagnetic metal and semiconductor in order to achieve a high spin injection and detection efficiency. (C) 2003 Published by Elsevier B.V.

DOI： 10.1016/S1567-1739(03)00106-8

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Spin-selective transport of optically excited polarized electrons through Fe/GaAs(100) and Fe/AlOx/GaAs(100) interfaces is reported. A visible enhancement in the spin selectivity is observed in the Fe/AlOx/GaAs(100) structure at a forward bias of 0.04 V, while no such feature is seen in the Fe/GaAs(100) structure. The spin selectivity in the Fe/AlOx/GaAs(100) structure has a maximum value which is a factor of 2 larger than that of the Fe/GaAs(100) structure at the same bias of 0.04 V. The effect can be understood in terms of the spin dependent tunneling of electrons through the oxide barrier in the Fe/AlOx/GaAs(100) structure, while its clear bias dependence excludes magnetic circular dichroism as a possible mechanism.

DOI： 10.1103/PhysRevB.68.134430

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Other Link： http://orcid.org/0000-0003-3683-5416

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The authors present magnetoresistance characteristics of patterned (Ga,Mn)As wire structures, which depend on wire width and thus overall magnetic anisotropy. Cubic and uniaxial magnetocrystalline anisotropies seem to be the, dominant magnetic contributions in 2-mum-wide wires, whereas both magnetocrystalline and shape-induced anisotropies, contribute to magnetization reversal in 1mum-wide wires, as manifested by jumps in the magnetoresistance curves. The role of these two anisotropies in the magnetization reversal is discussed, together with the determination of magnetic easy/hard axes of (Ga,Mn)As wires.

DOI： 10.1109/TMAG.2003.815710

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Scopus

J-GLOBAL

Language：English   Publishing type：Research paper (international conference proceedings)  

The anomalous Hall resistivities of polycrystalline manganite thin films with different grain sizes were analyzed. Positive anomalous Hall coefficients due to grain boundaries were observed in addition to a negative contribution in the bulk manganite. The temperature dependence of the anomalous Hall resistivity was found to be in agreement with its magnetoresistive feature.

DOI： 10.1063/1.1543865

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Scopus

J-GLOBAL

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

A double perovskite. type compound Sr2FeMoO6 was synthesized by a solid-state reaction. The order parameter (x) of Fe and Pt ions on the B sites increased from 68% to 82% and the spontaneous magnetization at 5 K increased from 2.1 to 3.0 mu(B) per formula unit by lowering the calcination temperature from 1100 to 500degreesC. The dependence of the spontaneous magnetization on x was discussed using two models considering the local magnetic interactions between ions on the B sites. Fe-57 Mossbauer analysis suggested the existence of tiny areas of SrFeO3-delta in Sr2FeMoO6. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1544088

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Spin injection is found to have a significant effect on the transport properties of the Kondo alloy Cu(Fe). When a spin-polarized electron current flows from Co into Cu(Fe) wires through the Co/Cu(Fe) interface, the resistivity of the Cu(Fe) wire is suppressed near the interface, as distinct from the ordinary logarithmic increase in the resistivity at low temperatures. For the opposite current direction, no significant changes are observed. The asymmetry of the resistivity with respect to the current direction decays with a characteristic length of 1.5+/-0.4 mum at 2.5 K as the distance from the interface is increased. Possible mechanisms for the asymmetry are discussed.

DOI： 10.1103/PhysRevLett.90.016601

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

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

We report on the magnetoresistive features of well-characterized polycrystalline manganite thin films as a function of film thickness. A crossover of the magnetization process from domain wall displacement to magnetic rotation of each grain is observed around a thickness of 25 nm, accompanied with the maximum of the coercivity. The thickness dependence of the electrical resistivity clearly distinguishes the transport mechanism at 25 nm, below which the magnetoresistance can be well scaled by similar to(M/M-S)(2), using the magnetization M and the saturation magnetization M-S. Spin-polarized tunneling transport between adjacent grains provides a comprehensive picture for the magnetotransport data. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1528282

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Magnetization and ac susceptibility measurements of Pd98.0Fe2.0 fine particles (average radii of 7.6-20.4 nm) gave the evidence of magnetic ordering of the surface layer in fine particle. The magnetic transition temperature of the surface layer in Pd-Fe fine particles was determined to be about 40 K based on the peaks in nonlinear susceptibility, and it slightly decreased with decreasing the particles size. Moreover, the size dependence of saturation magnetization indicates that the surface layer has no saturation magnetization at low temperature.

DOI： 10.1109/TMAG.2002.801968

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J-GLOBAL

Language：English   Publishing type：Research paper (international conference proceedings)  

Spin injection from a ferromagnetic metal Co into a Kondo alloy CuFe is demonstrated using the devices with a Co/CuFe wire junction. The temperature dependent resistivity of CuFe shows an increase below 20 K as spin current flows from CuFe into Co as seen in Kondo alloys. In contrast, the resistivity for the opposite current direction from Co into CnFe decreases at low temperatures at a current of 250 μA. The difference between the resistivities of both the current directions logarithmically increases with decreasing temperature, indicating the suppression of the spin scattering at Fe impurities that causes the logarithmic increase in Kondo alloys.

DOI： 10.1109/TMAG.2002.803135

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Scopus

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