Faculty Profiles - TANIYAMA Tomoyasu

Papers - TANIYAMA Tomoyasu

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Optically spin oriented electron transmission across fully epitaxial Fe(3)O(4)/GaAs(001) interfaces Reviewed International journal

T. Taniyama, T. Mori, K. Watanabe, E. Wada, M. Itoh, H. Yanagihara

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 7 ) page： 07D705/1 - 3 2008.4

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

Crossover of electron transmission mechanism and spin filtering effect at Fe/GaAs(001) interfaces Reviewed International journal

E. Wada, M. Itoh, T. Taniyama

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 7 ) page： 07A702/1 - 3 2008.4

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

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

Piezoelectric properties of lithium modified silver niobate perovskite single crystals Reviewed International journal

Desheng Fu, Makoto Endo, Hiroki Taniguchi, Tomoyasu Taniyama, Shin-ya Koshihara, Mitsuru Itoh

APPLIED PHYSICS LETTERS Vol. 92 ( 17 ) page： 172905/1 - 3 2008.4

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

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

Size dependence of martensite transformation temperature in ferromagnetic shape memory alloy FePd Reviewed International journal Open Access

Kenta Seki, Hiroaki Kura, Tetsuya Sato, Tomoyasu Taniyama

JOURNAL OF APPLIED PHYSICS Vol. 103 ( 6 ) page： 63910/1 - 9 2008.3

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

Origin of giant dielectric response in nonferroelectric CaCu3Ti4O12: Inhomogeneous conduction nature probed by atomic force microscopy Reviewed International journal

Desheng Fu, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Shin-ya Koshihara

CHEMISTRY OF MATERIALS Vol. 20 ( 5 ) page： 1694 - 1698 2008.3

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

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

High temperature ferromagnetism in single crystalline dilute Fe-doped BaTiO3 Reviewed International journal

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

PHYSICAL REVIEW B Vol. 77 ( 10 ) page： 104416/1 - 6 2008.3

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

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

Structural and magnetic characterization of Mn-doped ZnO films grown by spray pyrolysis method Reviewed International journal

Kenji Yoshino, Satoshi Oyama, Minoru Yoneta, Tomoyasu Taniyama

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS Vol. 148 ( 1-3 ) page： 234 - 236 2008.2

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

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

Novel ordering of an S=1/2 quasi-1D Ising-like antiferromagnet in magnetic field Reviewed International journal Open Access

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

PHYSICAL REVIEW LETTERS Vol. 100 ( 5 ) page： 057202/1 - 4 2008.2

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

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

Oscillatory changes in the tunneling magnetoresistance effect in semiconductor quantum-dot spin valves Reviewed International journal

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

PHYSICAL REVIEW B Vol. 77 ( 8 ) page： 081302(R)/1 - 4 2008.2

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

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

Selective Manipulation of Electron Spins with Electric Fields Reviewed

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

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

Kondo effect in a semiconductor quantum dot coupled to ferromagnetic electrodes Reviewed International journal Open Access

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

APPLIED PHYSICS LETTERS Vol. 91 ( 23 ) page： 232105/1 - 3 2007.12

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

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

PHYSICAL REVIEW LETTERS Vol. 99 ( 8 ) page： 087602/1 - 4 2007.8

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

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

Electric-field control of tunneling magnetoresistance effect in a Ni/InAs/Ni quantum-dot spin valve Reviewed International journal Open Access

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

APPLIED PHYSICS LETTERS Vol. 91 ( 2 ) page： 022107/1 - 3 2007.7

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

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh, Yutaka Ueda

CRYSTAL GROWTH & DESIGN Vol. 7 ( 6 ) page： 1055 - 1057 2007.6

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

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

AgNbO3: A lead-free material with large polarization and electromechanical response Reviewed International journal

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

APPLIED PHYSICS LETTERS Vol. 90 ( 25 ) page： 252907/1 - 3 2007.6

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

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

JOURNAL OF APPLIED PHYSICS Vol. 101 ( 9 ) page： 09F512/1 - 3 2007.5

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

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

Ferromagnetism at the surface of a LaCoO3 single crystal observed using scanning SQUID microscopy Reviewed International journal

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

PHYSICAL REVIEW B Vol. 75 ( 18 ) page： 184426/1 - 5 2007.5

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

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

Size and field effect on mesoscopic spin glass Reviewed International journal

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 310 ( 2 ) page： 1500 - 1502 2007.3

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

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

Two magnetic phase transitions in quasi-one-dimensional system SrCo2V2O8 Reviewed International journal

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

SOLID STATE COMMUNICATIONS Vol. 141 ( 12 ) page： 667 - 670 2007.3

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

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

Surface ferromagnetism of LaCoO3 crystals Reviewed International journal

A. Harada, T. Taniyama, M. Itoh

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 310 ( 2 ) page： 2172 - 2173 2007.3

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

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

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