Faculty Profiles - TANIYAMA Tomoyasu

Papers - TANIYAMA Tomoyasu

Division display 161 - 180 of about 236 ／ All the affair displays >>

Spin-glass behavior in zero magnetic field using tunnel resistance Reviewed International journal

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 310 ( 2 ) page： 1503 - 1505 2007.3

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

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

Spin transport through a single self-assembled InAs quantum dot with ferromagnetic leads Reviewed International journal Open Access

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

APPLIED PHYSICS LETTERS Vol. 90 ( 5 ) page： 053108 2007.1

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

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

FERROELECTRICS Vol. 347 ( 1 ) page： 140 - 144 2007

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

Long-range antiferromagnetic ordering in Cu2NiB2O6 Reviewed International journal

Zhangzhen He, Toru Kyomen, Tomoyasu Taniyama, Mitsuru Itoh

JOURNAL OF SOLID STATE CHEMISTRY Vol. 179 ( 12 ) page： 3937 - 3941 2006.12

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

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

Magnetic behavior and structural feature of quasi-one-dimensional BaCu(2)V2O(8) crystal Reviewed International journal

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 306 ( 2 ) page： 277 - 280 2006.11

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

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

Crystal growth and magnetic properties of SrCO2V2O8 Reviewed International journal

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh

JOURNAL OF CRYSTAL GROWTH Vol. 293 ( 2 ) page： 458 - 461 2006.8

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

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

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

Magnetic anisotropy switching in (Ga,Mn)As with increasing hole concentration Reviewed International journal Open Access

K. Hamaya, T. Watanabe, T. Taniyama, A. Oiwa, Y. Kitamoto, Y. Yamazaki

PHYSICAL REVIEW B Vol. 74 ( 4 ) page： 045201/1 - 4 2006.7

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

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

Effect of the shape anisotropy on the magnetic configuration of (Ga,Mn)As and its evolution with temperature Reviewed International journal Open Access

K Hamaya, T Taniyama, T Koike, Y Yamazaki

JOURNAL OF APPLIED PHYSICS Vol. 99 ( 12 ) page： 123901/1 - 3 2006.6

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

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

Antiferromagnetic-paramagnetic transitions in longitudinal and transverse magnetic fields in a SrCo2V2O8 crystal Reviewed International journal

ZZ He, T Taniyama, M Itoh

PHYSICAL REVIEW B Vol. 73 ( 21 ) page： 212406/1 - 4 2006.6

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

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

Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations Reviewed International journal Open Access

K.Hamaya, T. Taniyama, Y. Yamazaki

J. Appl. Phys. Vol. 99 ( 9 ) page： 093903/1 - 5 2006.5

Analysis of atomic arrangement in magnetic Fe-Pt nanoparticles Reviewed International journal

H Sakuma, T Taniyama, K Ishii, Y Kitamoto, Y Yamazaki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 300 ( 2 ) page： 284 - 292 2006.5

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

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

Electronic properties of the metallic pyrochlore ruthenates Pb2Ru2O6.5 and Bi2Ru2O7 Reviewed International journal

Makoto Tachibana, Yoshimitsu Kohama, Tomotaka Shimoyama, Akihiro Harada, Tomoyasu Taniyama, Mitsuru Itoh, Hitoshi Kawaji, Tooru Atake

PHYSICAL REVIEW B Vol. 73 ( 19 ) page： 193107/1 - 4 2006.5

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

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

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

Optically pumped spin-polarized carrier transport across Fe wire/GaAs interfaces Reviewed International journal

T Taniyama, E Wada, Y Yamazaki

JOURNAL OF APPLIED PHYSICS Vol. 99 ( 8 ) page： 08T307/1 - 3 2006.4

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

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

Dynamic relaxation of magnetic clusters in a ferromagnetic (Ga,Mn)As epilayer Reviewed International journal Open Access

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

PHYSICAL REVIEW B Vol. 73 ( 15 ) page： 155204/1 - 7 2006.4

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

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

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

Growth behavior and surface feature of quasi-one-dimensional anisotropic antiferromagnet BaCo2V2O8 crystal International journal

ZZ He, T Taniyama, M Itoh

JOURNAL OF CRYSTAL GROWTH Vol. 289 ( 2 ) page： 734 - 736 2006.4

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

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

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

Large magnetic anisotropy in the quasi-one-dimensional system BaCo2V2O8 Reviewed International journal

Z He, T Taniyama, M Itoh

APPLIED PHYSICS LETTERS Vol. 88 ( 13 ) page： 132504/1 - 3 2006.3

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

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

High field magnetism of the quasi one-dimensional anisotropic antiferromagnet BaCO2V2O8 Reviewed Open Access

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

YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS Vol. 51 page： 99-+ 2006

Optical studies of electron spin transmission Reviewed

Bland J.

Ultrathin Magnetic Structures IV: Applications of Nanomagnetism page： 59-100 2005.12

Field-induced order-disorder transition in the quasi-one-dimensional anisotropic antiferromagnet BaCo2V2O8 Reviewed International journal

Zhangzhen He, Tomoyasu Taniyama, Tôru Kyômen, Mitsuru Itoh

Physical Review B - Condensed Matter and Materials Physics Vol. 72 ( 17 ) page： 172403/1 - 4 2005.11

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

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

Magnetotransport measurement of (Ga,Mn)As epilayers with low-temperature annealing Reviewed International journal

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

ELECTROCHIMICA ACTA Vol. 51 ( 5 ) page： 1004 - 1007 2005.11

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

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

　 PREV - NEXT 　

1
2
3
4
5
6
7
8
9
10
11
12