Faculty Profiles - TANIYAMA Tomoyasu

Papers - TANIYAMA Tomoyasu

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Correlation between ferromagnetism and hole localization in very thin (Ga,Mn)As epilayers Reviewed International journal

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

JOURNAL OF APPLIED PHYSICS Vol. 97 ( 10 ) page： 10D301/1 - 3 2005.5

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

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

Effect of Ga+ irradiation on magnetic and magnetotransport properties in (Ga,Mn)As epilayers Reviewed International journal Open Access

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

JOURNAL OF APPLIED PHYSICS Vol. 97 ( 10 ) page： 10D302/1 - 3 2005.5

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

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

Mixed magnetic phases in (Ga,Mn)As epilayers Reviewed International journal Open Access

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

PHYSICAL REVIEW LETTERS Vol. 94 ( 14 ) page： 147203/1 - 4 2005.4

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 < 100 > cubic anisotropy. A change in the magnetic easy axis from [100] to [110] with increasing temperature can be explained by the reduced contribution of < 100 > cubic anisotropy to the magnetic properties above the transition temperature of the (Ga,Mn)As matrix.

DOI： 10.1103/PhysRevLett.94.147203

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

XMCD study of dilutely Fe doped Pd fine particles Reviewed International journal

T Shinohara, M Shigemune, T Sato, T Taniyama, H Sakurai

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 74 ( 3 ) page： 1044 - 1048 2005.3

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

Spin selective transport at the ferromagnetic wire/GaAs interface Reviewed International journal

T Taniyama, K Hamaya, Y Yamazaki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 286 ( 3 ) page： 103 - 107 2005.2

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

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

Influence of chemical conditions in fabrication of Bi-YIG precursor on morphological and magneto-optical response of its particulate film Reviewed

Kuroda CS, Uchida K, Ikazaki F, Taniyama T, Kitamoto Y, Yamazaki Y

NINTH INTERNATIONAL CONFERENCE ON FERRITES (ICF-9) page： 425-430 2005

Ion irradiation control of ferromagnetism in (Ga,Mn)As Reviewed Open Access

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 44 ( 24-27 ) page： L816-L818 2005

Effect of annealing on the transport process in manganite thin films Reviewed

Taniyama T, Hamaya K, Yamazaki Y

NINTH INTERNATIONAL CONFERENCE ON FERRITES (ICF-9) page： 189-194 2005

Anode products of a direct ethanol PEM fuel cell in a circulating fuel operation mode Reviewed Open Access

Taneda K, Taniyama T, Yamazaki Y

ELECTROCHEMISTRY Vol. 72 ( 10 ) page： 700-702 2004.10

Low temperature preparation and performance of Ni/YSZ anode with a multi-layered structure for SOFC Reviewed International journal

T Hatae, N Kakuda, T Taniyama, Y Yamazaki

JOURNAL OF POWER SOURCES Vol. 135 ( 1-2 ) page： 25 - 28 2004.9

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

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

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

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

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

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

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

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

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

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

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

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

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