研究者詳細 - 谷山　智康

論文 - 谷山　智康

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Crystal growth and magnetic properties of SrCO2V2O8 査読有り国際誌

Zhangzhen He, Tomoyasu Taniyama, Mitsuru Itoh

JOURNAL OF CRYSTAL GROWTH 293 巻 ( 2 ) 頁： 458 - 461 2006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：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

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

Magnetic anisotropy switching in (Ga,Mn)As with increasing hole concentration 査読有り国際誌

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

PHYSICAL REVIEW B 74 巻 ( 4 ) 頁： 045201/1 - 4 2006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 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

その他リンク： 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 査読有り国際誌

K Hamaya, T Taniyama, T Koike, Y Yamazaki

JOURNAL OF APPLIED PHYSICS 99 巻 ( 12 ) 頁： 123901/1 - 3 2006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

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 査読有り国際誌

ZZ He, T Taniyama, M Itoh

PHYSICAL REVIEW B 73 巻 ( 21 ) 頁： 212406/1 - 4 2006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：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

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

Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations 査読有り国際誌

K.Hamaya, T. Taniyama, Y. Yamazaki

J. Appl. Phys. 99 巻 ( 9 ) 頁： 093903/1 - 5 2006年5月

Analysis of atomic arrangement in magnetic Fe-Pt nanoparticles 査読有り国際誌

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

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 300 巻 ( 2 ) 頁： 284 - 292 2006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：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

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

Electronic properties of the metallic pyrochlore ruthenates Pb2Ru2O6.5 and Bi2Ru2O7 査読有り国際誌

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

PHYSICAL REVIEW B 73 巻 ( 19 ) 頁： 193107/1 - 4 2006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

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

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

Optically pumped spin-polarized carrier transport across Fe wire/GaAs interfaces 査読有り国際誌

T Taniyama, E Wada, Y Yamazaki

JOURNAL OF APPLIED PHYSICS 99 巻 ( 8 ) 頁： 08T307/1 - 3 2006年4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

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

Growth behavior and surface feature of quasi-one-dimensional anisotropic antiferromagnet BaCo2V2O8 crystal 国際誌

ZZ He, T Taniyama, M Itoh

JOURNAL OF CRYSTAL GROWTH 289 巻 ( 2 ) 頁： 734 - 736 2006年4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

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

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

Dynamic relaxation of magnetic clusters in a ferromagnetic (Ga,Mn)As epilayer 査読有り国際誌

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

PHYSICAL REVIEW B 73 巻 ( 15 ) 頁： 155204/1 - 7 2006年4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

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

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

Large magnetic anisotropy in the quasi-one-dimensional system BaCo2V2O8 査読有り国際誌

Z He, T Taniyama, M Itoh

APPLIED PHYSICS LETTERS 88 巻 ( 13 ) 頁： 132504/1 - 3 2006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 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 査読有り

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 51 巻頁： 99-+ 2006年

Optical studies of electron spin transmission 査読有り

Bland J.

Ultrathin Magnetic Structures IV: Applications of Nanomagnetism 頁： 59-100 2005年12月

Field-induced order-disorder transition in the quasi-one-dimensional anisotropic antiferromagnet BaCo2V2O8 査読有り国際誌

Zhangzhen He, Tomoyasu Taniyama, Tôru Kyômen, Mitsuru Itoh

Physical Review B - Condensed Matter and Materials Physics 72 巻 ( 17 ) 頁： 172403/1 - 4 2005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：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

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

Magnetotransport measurement of (Ga,Mn)As epilayers with low-temperature annealing 査読有り国際誌

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

ELECTROCHIMICA ACTA 51 巻 ( 5 ) 頁： 1004 - 1007 2005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：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

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

Correlation between ferromagnetism and hole localization in very thin (Ga,Mn)As epilayers 査読有り国際誌

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

JOURNAL OF APPLIED PHYSICS 97 巻 ( 10 ) 頁： 10D301/1 - 3 2005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

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 査読有り国際誌

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

JOURNAL OF APPLIED PHYSICS 97 巻 ( 10 ) 頁： 10D302/1 - 3 2005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 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 査読有り国際誌

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

PHYSICAL REVIEW LETTERS 94 巻 ( 14 ) 頁： 147203/1 - 4 2005年4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

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

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

XMCD study of dilutely Fe doped Pd fine particles 査読有り国際誌

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 巻 ( 3 ) 頁： 1044 - 1048 2005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：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 査読有り国際誌

T Taniyama, K Hamaya, Y Yamazaki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 286 巻 ( 3 ) 頁： 103 - 107 2005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

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

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

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