研究者詳細 - 谷山　智康

論文 - 谷山　智康

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High temperature ferromagnetism in single crystalline dilute Fe-doped BaTiO3 査読有り国際誌

Sugata Ray, Priya Mahadevan, Suman Mandal, S. R. Krishnakumar, Carlos Seiti Kuroda, T. Sasaki, Tomoyasu Taniyama, Mitsuru Itoh

PHYSICAL REVIEW B 77 巻 ( 10 ) 頁： 104416/1 - 6 2008年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Structural and magnetic characterization of Mn-doped ZnO films grown by spray pyrolysis method 査読有り国際誌

Kenji Yoshino, Satoshi Oyama, Minoru Yoneta, Tomoyasu Taniyama

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS 148 巻 ( 1-3 ) 頁： 234 - 236 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Novel ordering of an S=1/2 quasi-1D Ising-like antiferromagnet in magnetic field 査読有り国際誌

S. Kimura, T. Takeuchi, K. Okunishi, M. Hagiwara, Z. He, K. Kindo, T. Taniyama, M. Itoh

PHYSICAL REVIEW LETTERS 100 巻 ( 5 ) 頁： 057202/1 - 4 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

その他リンク： http://orcid.org/0000-0003-3683-5416

Oscillatory changes in the tunneling magnetoresistance effect in semiconductor quantum-dot spin valves 査読有り国際誌

K. Hamaya, M. Kitabatake, K. Shibata, M. Jung, M. Kawamura, S. Ishida, T. Taniyama, K. Hirakawa, Y. Arakawa, T. Machida

PHYSICAL REVIEW B 77 巻 ( 8 ) 頁： 081302(R)/1 - 4 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Selective Manipulation of Electron Spins with Electric Fields 査読有り

Pioro-Ladriere Michel, Obata Toshiaki, Tokura Yasuhiro, Shin You-Sok, Kubo Toshihiro, Yoshida Katsuharu, Taniyama Tomoyasu, Tarucha Seigo

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT ( 176 ) 頁： 322-340 2008年

Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes 査読有り国際誌

K. Hamaya, M. Kitabatake, K. Shibata, M. Jung, M. Kawamura, K. Hirakawa, T. Machida, T. Taniyama, S. Ishida

APPLIED PHYSICS LETTERS 91 巻 ( 23 ) 頁： 232105/1 - 3 2007年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

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

Field-induced order-disorder transition in antiferromagnetic BaCo2V2O8 driven by a softening of spinon excitation 査読有り国際誌

S. Kimura, H. Yashiro, K. Okunishi, M. Hagiwara, Z. He, K. Kindo, T. Taniyama, M. Itoh

PHYSICAL REVIEW LETTERS 99 巻 ( 8 ) 頁： 087602/1 - 4 2007年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

その他リンク： http://orcid.org/0000-0003-3683-5416

Electric-field control of tunneling magnetoresistance effect in a Ni/InAs/Ni quantum-dot spin valve 査読有り国際誌

K. Hamaya, M. Kitabatake, K. Shibata, M. Jung, M. Kawamura, K. Hirakawa, T. Machida, T. Taniyama, S. Ishida, Y. Arakawa

APPLIED PHYSICS LETTERS 91 巻 ( 2 ) 頁： 022107/1 - 3 2007年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

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

Flux growth and magnetic anomalies of Co3V2O8 crystals 査読有り国際誌

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh, Yutaka Ueda

CRYSTAL GROWTH & DESIGN 7 巻 ( 6 ) 頁： 1055 - 1057 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

その他リンク： http://orcid.org/0000-0003-3683-5416

AgNbO3: A lead-free material with large polarization and electromechanical response 査読有り国際誌

Desheng Fu, Makoto Endo, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh

APPLIED PHYSICS LETTERS 90 巻 ( 25 ) 頁： 252907/1 - 3 2007年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

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

Electrical voltage manipulation of ferromagnetic microdomain structures in a ferromagnetic/ferroelectric hybrid structure 査読有り国際誌

T. Taniyama, K. Akasaka, D. Fu, M. Itoh, H. Takashima, B. Prijamboedi

JOURNAL OF APPLIED PHYSICS 101 巻 ( 9 ) 頁： 09F512/1 - 3 2007年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

その他リンク： http://orcid.org/0000-0003-3683-5416

Ferromagnetism at the surface of a LaCoO3 single crystal observed using scanning SQUID microscopy 査読有り国際誌

A. Harada, T. Taniyama, Y. Takeuchi, T. Sato, T. Kyomen, M. Itoh

PHYSICAL REVIEW B 75 巻 ( 18 ) 頁： 184426/1 - 5 2007年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMERICAN PHYSICAL SOC

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Size and field effect on mesoscopic spin glass 査読有り国際誌

K. Komatsu, H. Maki, T. Taniyama, T. Sato

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 1500 - 1502 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Surface ferromagnetism of LaCoO3 crystals 査読有り国際誌

A. Harada, T. Taniyama, M. Itoh

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 2172 - 2173 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Spin-glass behavior in zero magnetic field using tunnel resistance 査読有り国際誌

Y. Takeuchi, K. Komatsu, H. Maki, T. Taniyama, T. Sato

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 1503 - 1505 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

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

その他リンク： http://orcid.org/0000-0003-3683-5416

Two magnetic phase transitions in quasi-one-dimensional system SrCo2V2O8 査読有り国際誌

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh, Jun-Ichi Yamaura, Yutaka Ueda

SOLID STATE COMMUNICATIONS 141 巻 ( 12 ) 頁： 667 - 670 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

その他リンク： http://orcid.org/0000-0003-3683-5416

Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads 査読有り国際誌

K. Hamaya, S. Masubuchi, M. Kawamura, T. Machida, M. Jung, K. Shibata, K. Hirakawa, T. Taniyama, S. Ishida, Y. Arakawa

APPLIED PHYSICS LETTERS 90 巻 ( 5 ) 頁： 053108 2007年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

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

Conductive Boundary Layer in CaCu3Ti4O12 with Giant-Dielectric-Response 査読有り国際誌

Desheng Fu, Yosuke Arima, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Jianding Yu, Shin-Ya Koshihara

FERROELECTRICS 347 巻 ( 1 ) 頁： 140 - 144 2007年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

Long-range antiferromagnetic ordering in Cu2NiB2O6 査読有り国際誌

Zhangzhen He, Toru Kyomen, Tomoyasu Taniyama, Mitsuru Itoh

JOURNAL OF SOLID STATE CHEMISTRY 179 巻 ( 12 ) 頁： 3937 - 3941 2006年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

その他リンク： http://orcid.org/0000-0003-3683-5416

Magnetic behavior and structural feature of quasi-one-dimensional BaCu(2)V2O(8) crystal 査読有り国際誌

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 306 巻 ( 2 ) 頁： 277 - 280 2006年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

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

その他リンク： http://orcid.org/0000-0003-3683-5416

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