Faculty Profiles - TANIYAMA Tomoyasu

Proton conductivity of zirconium tricarboxybutylphosphonate/PBI nanocomposite membrane Reviewed International journal

Y Yamazaki, MY Jang, T Taniyama

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Vol. 5 ( 4 ) page： 455 - 459 2004.7

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

Significant change in in-plane magnetic anisotropy of (Ga,Mn)As epilayer induced by low-temperature annealing Reviewed International journal

H Kato, K Hamaya, T Taniyama, Y Kitamoto, H Munekata

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 43 ( 7A ) page： L904 - L906 2004.7

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

Anistropic magnetotransport due to uniaxial magnetic anisotropy in (Ga,Mn)As wires Reviewed International journal

K Hamaya, T Taniyama, Y Kitamoto, Y Yamazaki, R Moriya, H Munekata

IEEE TRANSACTIONS ON MAGNETICS Vol. 40 ( 4 ) page： 2682 - 2684 2004.7

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

Anisotropy field distribution of partially ordered FePt nanoparticles Reviewed International journal

H Sakuma, T Taniyama, Y Kitamoto, Y Yamazaki, H Nishio, H Yamamoto

JOURNAL OF APPLIED PHYSICS Vol. 95 ( 11 ) page： 7261 - 7263 2004.6

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

Ferromagnetism of gas-evaporated Pd fine particles in mesoscopic size Reviewed International journal

Takenao Shinohara, Tetsuya Sato, T. Taniyama

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 272 page： E1181 - E1182 2004.5

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

Contribution of Shape Anisotropy to the Magnetic Configuration of (Ga, Mn)As Reviewed

Hamaya K.

Japanese Journal of Applied Physics, Part 2: Letters Vol. 43 ( 2 B ) page： . 2004.2

Magnetotransport study of temperature dependent magnetic anisotropy in a (Ga,Mn)As epilayer Reviewed International journal

K Hamaya, T Taniyama, Y Kitamoto, R Moriya, H Munekata

JOURNAL OF APPLIED PHYSICS Vol. 94 ( 12 ) page： 7657 - 7661 2003.12

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 <100>, 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

Scopus

Surface ferromagnetism of Pd fine particles Reviewed International journal

T Shinohara, T Sato, T Taniyama

PHYSICAL REVIEW LETTERS Vol. 91 ( 19 ) page： 197201/1 - 4 2003.11

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

Spin selective transport at the ferromagnet/semiconductor interface Reviewed International journal

JAC Bland, T Taniyama, WS Cho, SJ Steinmueller

CURRENT APPLIED PHYSICS Vol. 3 ( 5 ) page： 429 - 432 2003.10

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

Spin-selective transport through Fe/AlOx/GaAs(100) interfaces under optical spin orientation Reviewed International journal

T Taniyama, G Wastlbauer, A Ionescu, M Tselepi, JAC Bland

PHYSICAL REVIEW B Vol. 68 ( 13 ) page： 134430/1 - 4 2003.10

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

Control of magnetic anisotropy and magnetotransport in epitaxial micropatterned (Ga,Mn)As wire structures Reviewed International journal

K Hamaya, R Moriya, A Oiwa, T Taniyama, Y Kitamoto, H Munekata

IEEE TRANSACTIONS ON MAGNETICS Vol. 39 ( 5 ) page： 2785 - 2787 2003.9

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

Scopus

Anomalous hall resistivity due to grain boundary in manganite thin films Reviewed International journal

T. Taniyama, K. Hamaya, Y. Kitamoto, Y. Yamazaki

Journal of Applied Physics Vol. 93 ( 10 ) page： 8107 - 8109 2003.5

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

Scopus

Cation order and magnetic properties of double perovskite Sr2FeMoO6 Reviewed International journal

H Sakuma, T Taniyama, Y Kitamoto, Y Yamazaki

JOURNAL OF APPLIED PHYSICS Vol. 93 ( 5 ) page： 2816 - 2819 2003.3

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

Asymmetric transport due to spin injection into a Kondo alloy Reviewed International journal

T Taniyama, N Fujiwara, Y Kitamoto, Y Yamazaki

PHYSICAL REVIEW LETTERS Vol. 90 ( 1 ) page： 016601/1 - 4 2003.1

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