Faculty Profiles - SHIGETA Iduru

Masakazu Ito, Tatsuya Furuta, Keita Kai, Atsushi Taira, Keijiro Onda, Iduru Shigeta, Masahiko Hiroi . Thermodynamic Properties of Heusler Fe2-xCox MnSi . JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS428 390 - 393 2017.4Reviewed International journal

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

We investigated the thermodynamic properties of Heusler compounds Fe2-xCox mnSi (0.00 <= x <= 2.00). The specific heats CP(T) for compounds with x <= 0.1 exhibit a.-type anomaly arising from spin rearrangements at TR. With increasing x, TR decreases linearly and vanishes at x similar to 0.169. The magnetic entropy, S-TR, derived from the magnetic specific heat, Cm(T), released at TR decreases by increasing x. This means the canting angle of spins from the [111] direction decreases by the substitution of Fe atoms with Co atoms, based on the magnetic structure model of Fe2MnSi proposed by Miles et al. For compounds with 0.5 <= x, CP(T) in the low-T range can be reproduced by Debye T-3 law. The electronic specific heat coefficient decreases monotonically with x.

DOI： 10.1016/j.jmmm.2016.12.070

Masahiko Hiroi, Hiroaki Sano, Tomoya Tazoko, Iduru Shigeta, Masakazu Ito, Keiichi Koyama, Hirotaka Manaka, Norio Terada, Muneaki Fujii, Akihiro Kondo, Koichi Kindo . Magnetic and electrical properties of Heusler compounds Ru2Cr1-xXxSi (X = V, Ti) . JOURNAL OF ALLOYS AND COMPOUNDS694 1376 - 1382 2017.2Reviewed International journal

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

Two series of Heusler compounds Ru2Cr1-xXxSi (X = V, Ti) are synthesized, and their magnetic and electrical properties are investigated. Overall, these two series of compounds are identical in numerous properties. The measurements of magnetic properties reveal that an antiferromagnetic transition observed for x = 0 becomes smeared and it changes into a spin-glass state with increasing x. Around x = 0.5 this behavior disappears and it becomes paramagnetic. High-field magnetization for x = 03 and 0.4 up to 62 T exhibits no sign of magnetic transition or saturation of the magnetization. In the temperature dependence of resistivity, the kink that indicates the antiferromagnetic transition observed for x = 0 becomes invisible even for x similar to 0.1. This also exemplifies that the antiferromagnetic order is destroyed by the substitution and is replaced by the spin-glass state. Concerning the resistivity, these samples exhibit semiconducting behavior for small x, whereas with increasing x >= 0.5 they turn to show metallic behavior and Ru2VSi becomes a paramagnetic metal. Nevertheless, Ru2TiSi shows a tendency for semiconductivity again. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2016.09.276

Masahiko Hiroi, Tomoya Tazoko, Hiroaki Sano, Iduru Shigeta, Keiichi Koyama, Akihiro Kondo, Koich Kindo, Hirotaka Manaka, Norio Terada . High-field magnetization of Heusler compound Fe2Mn1-xVxSi . PHYSICAL REVIEW B95 ( 1 ) 014410-1 - 014410-5 2017.1Reviewed International journal

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

Fe2MnSi exhibits a ferromagnetic transition at T-C similar to 230 K and another transition to a phase with antiferromagnetic components at T-A similar to 60 K. By substituting V for Mn, so as to obtain Fe2Mn1-xVxSi, T-A is revealed to decrease with x and then vanish around x similar to 0.2. In this study, the phase boundary of the transition at T-A in the high-field range is found for 0 <= x <= 0.15 with pulsed fields up to similar to 70 T. The magnetization of Fe2Mn1-xVx Si slowly increases even at the highest field of similar to 70 T, though it occurs more gradually as x increases. We compare the magnetization for 0 <= x <= 0.20 at 62 T with the Slater-Pauling rule, which holds when a Heusler compound is a half-metal, and find fairly good agreement. This suggests an intimate relation between the high-field phase and the half-metallic electronic structure, and that at the high-field limit the phase approaches the half-metallic state, which has been predicted by band-structure calculations.

DOI： 10.1103/PhysRevB.95.014410

Ryutaro Ooka, Iduru Shigeta, Yoshimi Sukino, Yutaro Fujimoto, Rie Y. Umetsu, Yoshio Miura, Akiko Nomura, Kunio Yubuta, Touru Yamauchi, Takeshi Kanomata, Masahiko Hiroi . Magnetization and Spin Polarization of Heusler Alloys Co2TiSn and Co2TiGa0.5Sn0.5 . IEEE MAGNETICS LETTERS8 3101604-1 - 3101604-4 2017Reviewed International journal

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The substitution effect on half-metallicity for Co-based Heusler alloys Co2TiGa1-xSnx was investigated by experimental measurements and first-principles band calculations. The synthesized alloys crystalized in the ordered L2(1) crystal structure. The spontaneous magnetization obeyed the Slater-Pauling rule, indicating the possibility that Co2TiSn and Co2TiGa0.5Sn0.5 are half-metals. The first-principles band calculations revealed that Co2TiSn is half-metal and Co2TiGa0.5Sn0.5 is nearly half-metal. The spin polarization P was determined by the Andreev reflection technique. The intrinsic P values were 58.9% for Co2TiSn and 58.2% for Co2TiGa0.5Sn0.5, respectively. The P values of Co2TiGa1-xSnx were relatively higher than other Co-based Heusler alloys. Thus, Co-based Heusler alloys Co2TiGa1-xSnx are possible candidates for half-metallic electrode materials in spintronic devices.

DOI： 10.1109/LMAG.2016.2623257

Iduru Shigeta, Takahide Kubota, Kazumasa Makise, Shojiro Kimura, Satoshi Awaji, Bunju Shinozaki, Keiichi Koyama, Koki Takanashi, Masahiko Hiroi . Fabrication and Characterization of Epitaxial Films of Superconductor NbN and Highly Spin- Polarized Heusler Alloy CO2Fe0.4Mn0.6Si . IEEE MAGNETICS LETTERS8 3305605-1 - 3305605-5 2017Reviewed International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We report structural, magnetic, and transport properties of epitaxial films of superconductor NbN and highly spin- polarized Heusler alloy CO2Fe0.4Mn0.6Si (CFMS). The saturation magnetization Ms of the film was 870 emu/cm(3), which is slightly smaller than values reported earlier. With an increase of CFMS thickness d(CFMS), the sheet resistance R-sq decreased and the upper critical field mu H-0(c2)(0) decreased monotonically, while the superconducting transition temperature Tc exhibited a minimum around d(CFMS) = 3 nm. A theoretical analysis of superconducting fluctuations revealed that the high spin polarization of the CFMS layer affected the pair breaking parameter d, the superconducting coherence length. (0), and the diffusion coefficient D.

DOI： 10.1109/LMAG.2017.2687878

Ryutaro Ooka, Iduru Shigeta, Yoshimi Sukino, Yutaro Fujimoto, Rie Y. Umetsu, Akiko Nomura, Touru Yamauchi, Takeshi Kanomata, Kunio Yubuta, Masahiko Hiroi . Spin polarization and magnetization of Heusler alloys Co₂TiGa_1−xSn_x (x = 1.0, 0.5) . IEEE Magnetics Letters 2016.10Spin polarization and magnetization of Heusler alloys Co₂TiGa_1−xSn_x (x = 1.0, 0.5)Reviewed

Masahiko Hiroi, Hiroaki Sano, Tomoya Tazoko, Iduru Shigeta, Masakazu Ito, Keiichi Koyama, Hirotaka Manaka, Norio Terada, Muneaki Fujii, Akihiro Kondo, Koichi Kindo . Magnetic and electrical properties of Heusler compounds Ru₂Cr_1−xX_xSi (X = V, Ti) . Journal of Alloys and Compounds 2016.9Magnetic and electrical properties of Heusler compounds Ru₂Cr_1−xX_xSi (X = V, Ti)Reviewed

Qing Tao Meng, Shingo Komaki, Takuya Tsuneoka, Hirotoshi Hanada, Shohei Maeda, Taiki Murano, Fusao Ichikawa, Kikuo Itoh, Yuya Nishisako, Iduru Shigeta, Masahiko Hiroi . Tunneling spectroscopy of the superconductor-insulator transition on Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ and (Bi_1-yPb_y)₂Sr₂Ca_1-xY_xCu₂O_8+δ . IEEE Transactions on Applied Superconductivity24 ( 5 ) 7000504(1) - (4) 2014.10Tunneling spectroscopy of the superconductor-insulator transition on Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ and (Bi_1-yPb_y)₂Sr₂Ca_1-xY_xCu₂O_8+δReviewed

Qing Tao Meng, Shingo Komaki, Takuya Tsuneoka, Hirotoshi Hanada, Shohei Maeda, Taiki Murano, Fusao Ichikawa, Kikuo Itoh, Yuya Nishisako, Iduru Shigeta, Masahiko Hiroi . Tunneling Spectroscopy of the Superconductor-Insulator Transition on Bi2Sr2Ca1-xYxCu2O8+delta and (Bi1-yPby)(2)Sr2Ca1-xYxCu2O8+delta . IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY24 ( 5 ) 7000504-1 - 7000504-4 2014.10Reviewed International journal

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We report tunnel experiments on Bi2Sr2Ca1-xYxCu 2O8+delta (Y-Bi2212) crystals with x= 0, 0.01, 0.05, 0.1, 0.11, and 0.12. The results are discussed about Cooper pairs existing. Tunneling spectra were measured for Y-Bi2212 crystal-SiO-Ag planar junctions. For superconducting samples the V-shaped gap structure and zero bias conductance peaks (ZBCP) were observed. While neither superconducting gap nor ZBCP was observed for insulator samples. These results suggest that Cooper pairs break up on the insulating side of superconductor- insulator transition (SIT). We also measured tunneling spectra on (Bi1-Pb-y(y))(2)Sr2Ca1-xYxCu2O8+delta samples. In their spectra there were also several characteristic behaviors.

DOI： 10.1109/TASC.2014.2351263

Sora Nishiinoue, Hidekazu Suwa, Iduru Shigeta, Masahiko Hiroi, Keiichi Koyama, Shojiro Kimura, Kazuo Watanabe, Muneaki Fujii . Magneto-transport properties in the Heusler compounds Ru_2-xFe_xCrSi (0 ≦ x ≦ 0.1) . JPS Conference Proceedings3 017018(1) - (6) 2014.6Magneto-transport properties in the Heusler compounds Ru_2-xFe_xCrSi (0 ≦ x ≦ 0.1)Reviewed

Hidekazu Suwa, Sora Nishiinoue, Kensuke Koseki, Iduru Shigeta, Masakazu Ito, Masahiko Hiroi, Hirotaka Manaka, Norio Terada . Study on the half-Heusler compounds Co_1+δTiSb with excess cobalt . JPS Conference Proceedings3 017017(1) - (6) 2014.6Study on the half-Heusler compounds Co_1+δTiSb with excess cobaltReviewed

Masahiko Hiroi, Tomonari Higashiuchi, Takuro Ogawa, Iduru Shigeta, Masakazu Ito, Hirotaka Manaka, Norio Terada . Substitution effects in the antiferromagnetic Heusler compound Ru₂CrSi . JPS Conference Proceedings3 014024(1) - (6) 2014.6Substitution effects in the antiferromagnetic Heusler compound Ru₂CrSiReviewed

Masahiko Hiroi, Tomonari Higashiuchi, Takuro Ogawa, Iduru Shigeta, Masakazu Ito, Hirotaka Manaka, Norio Terada . Substitution effects in the antiferromagnetic Heusler compound Ru2CrSi . JPS Conference Proceedings3 014024-1 - 014024-6 2014.6Substitution effects in the antiferromagnetic Heusler compound Ru2CrSiReviewed International journal

Hidekazu Suwa, Sora Nishiinoue, Kensuke Koseki, Iduru Shigeta, Masakazu Ito, Masahiko Hiroi, Hirotaka Manaka, Norio Terada . Study on the half-Heusler compounds Co1+δTiSb with excess cobalt . JPS Conference Proceedings3 017017-1 - 017017-6 2014.6Study on the half-Heusler compounds Co1+δTiSb with excess cobaltReviewed International journal

Sora Nishiinoue, Hidekazu Suwa, Iduru Shigeta, Masahiko Hiroi, Keiichi Koyama, Shojiro Kimura, Kazuo Watanabe, Muneaki Fujii . Magneto-transport properties in the Heusler compounds Ru2−xFexCrSi (0 ≦ x ≦ 0.1) . 3 017018-1 - 017018-6 2014.6Magneto-transport properties in the Heusler compounds Ru2−xFexCrSi (0 ≦ x ≦ 0.1)Reviewed International journal

Iduru Shigeta, Yuya Nishisako, Shinpei Urakawa, Osamu Murayama, Masakazu Ito, and Masahiko Hiroi . Fabrication and measurement of high-temperature superconductor YBa₂Cu₃O_7-δ: Activity report of science club . JPS Conference Proceedings1 017013(1) - (4) 2014.3Fabrication and measurement of high-temperature superconductor YBa₂Cu₃O_7-δ: Activity report of science clubReviewed

Iduru Shigeta, Yuya Nishisako, Shinpei Urakawa, Osamu Murayama, Masakazu Ito, Masahiko Hiroi . Fabrication and measurement of high-temperature superconductor YBa2Cu3O7−δ: Activity report of science club . JPS Conference Proceedings1 017013-1 - 017013-4 2014.3Fabrication and measurement of high-temperature superconductor YBa2Cu3O7−δ: Activity report of science clubReviewed International journal

Iduru Shigeta, Yuki Maeda, Kohei Harumori, Yuya Nishisako, Masakazu Ito, Touru Yamauchi, and Masahiko Hiroi . Spin polarization measurements of Heusler alloy Ru_0.2Fe_1.8CrSi by Andreev reflection technique . IEEE Transactions on Magnetics50 ( 1 ) 1401304(1) - (4) 2014.1Spin polarization measurements of Heusler alloy Ru_0.2Fe_1.8CrSi by Andreev reflection techniqueReviewed

Iduru Shigeta, Yuki Maeda, Kohei Harumori, Yuya Nishisako, Masakazu Ito, Touru Yamauchi, Masahiko Hiroi . Spin Polarization Measurements of Heusler Alloy Ru0.2Fe1.8CrSi by Andreev Reflection Technique . IEEE TRANSACTIONS ON MAGNETICS50 ( 1 ) 1401304-1 - 1401304-4 2014.1Reviewed International journal

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We report spin polarization P of Fe-rich Heusler alloy Ru0.2Fe1.8CrSi, which was determined by the Andreev reflection technique. Heusler alloy Ru2-xFexCrSi was predicted to be half- metal by the first- principle band calculations. Fe- rich Ru0.2Fe1.8CrSi compounds are ferromagnetic and the saturation magnetization M-0 almost coincideswith that expected fromthe Slater- Pauling rule. Two theoretical approaches in the determination of spin polarization by Andreev reflection are discussed and compared from an experimental perspective. The spin polarization more than P = 0.60 is obtained for Ru0.2Fe1.8CrSi specimens and it is highest value in all Ru2-xFexCrSi compounds. The difference in values of spin polarization as determined by two models is less than 0.02.

DOI： 10.1109/TMAG.2013.2278034