研究者詳細 - 武田　直也

論文 - 武田　直也

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Coexistence of distinct Ce 4f-electron states at inequivalent crystallographic sites: CePtGe2 case

Hayato Muto, Tomohito Nakano, Tatsuya Watanabe, Ryota Takahashi, Naoya Takeda, Jun Gouchi, Yoshiya Uwatoko, Michal Dušek, Jan Prokleška, Jiří Pospíšil, Vladimír Sechovský

Journal of Magnetism and Magnetic Materials 613 172670 - 172670 2025年2月

First-order transition under a magnetic ordered state in SmPtSi2

Tomohito Nakano, Eisuke Takahashi, Shuto Yamaguchi, Naoya Takeda, Klára Uhlířová, Jan Prokleška, Jiří Pospíšil, Vladimír Sechovský, Kazuyuki Matusbayashi, Hanming Ma, Yoshiya Uwatoko

Physica Scripta 99 ( 8 ) 085923 - 085923 2024年7月

掲載種別：研究論文（学術雑誌）出版者・発行元：IOP Publishing

Abstract

We have synthesized polycrystalline and single-crystalline samples of SmPtSi2, and measured their resistivity, specific heat, magnetization, and Seebeck coefficient. The existence of two magnetic phase transitions has been confirmed, one at T H = 8.6 K and the other T L = 5.6 K. A hump-type anomaly in resistivity, a lambda-type anomaly in specific heat, a downward bend in magnetization, and a semiconductor-like increase in the Seebeck coefficient were observed at T H, indicating an antiferromagnetic transition accompanied by a gap opening on the Fermi surface. In contrast, a sharp drop in resistivity, a sharp spike in specific heat, and a drop in magnetization were observed at T L. The Seebeck coefficient showed metallic temperature dependence below T L. With increasing pressure, T H and T L shifted to higher temperatures. The transition at T L was no longer observed at pressures above 1.5 GPa. These findings suggest that the transition at T L is a transition from an antiferromagnetic ordered state with the gap on the Fermi surface to a different antiferromagnetic state.

DOI： 10.1088/1402-4896/ad59e0

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その他リンク： https://iopscience.iop.org/article/10.1088/1402-4896/ad59e0/pdf

Y-Substitution Effects on Electrical Resistivity of (Ce1−yYy)PtGe2

Hayato Muto, Shoma Onuma, Tatsuya Watanabe, Ryota Takahashi, Tomohito Nakano, Naoya Takeda, Jun Gouchi, Yoshiya Uwatoko, Klára Uhlířová, Jan Prokleška, Vladimír Sechovský

Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 2023年5月

La-Substitution Effects on Multisite Ce Compound CePtGe<inf>2</inf>

Hayato Muto, Shoma Onuma, Tomohito Nakano, Naoya Takeda, Jun Gouchi, Yoshiya Uwatoko, Klára Uhlířová, Jan Prokleška, Vladimír Sechovský

Journal of the Physical Society of Japan 91 ( 7 ) 2022年7月

掲載種別：研究論文（学術雑誌）

The CePtGe2 compound, which shows antiferromagnetic transition at Néel temperature TN = 3.8 K, has two crystallographically inequivalent Ce sites. Recently, the coexistence of a localized f-electron state at one of two Ce sites and an itinerant heavy f-electron state at the other Ce site has been suggested. In this study, we have prepared polycrystalline samples of (Ce1-xLax)PtGe2 (x = 0 ∼ 0.2) and have measured their electrical resistivity and magnetization. The specific heat for x = 0.2 has been measured also. With increasing x, the downward bending of the temperature dependence of the resistivity and the cusp-type anomaly in the susceptibility associated with TN shift to lower temperatures with a linear extrapolation of TN directing to 0 K at x ∼ 0.5. Also, the saturation magnetization decreases linearly with increasing x, pointing to the disappearance of magnetic moments at the same La concentration. These results indicate that only the Ce ions with the localized f-electron are substituted by La ions. On the other hand, the transition from the antiferromagnetic state to the ferromagnetic-like polarized magnetic state at a very weak magnetic field, which is comparable to that of conventional Ferrite magnets, was realized via the La-substitution.

DOI： 10.7566/JPSJ.91.074712

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Superconductivity of the ternary stannide Y5Co6Sn18

Naoki Kase, Taishi Anada, Yusuke Terui, Tomohito Nakano, Naoya Takeda

PHYSICA B-CONDENSED MATTER 587 2020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：ELSEVIER

Superconductivity is newly discovered in a single crystal of Y5Co6Sn18 at superconducting transition temperature T-c = 0.7 K. The single crystals are grown by a Sn flux method. Superconducting and normal properties of Y5Co6Sn18 are investigated by means of electrical resistivity rho(T) and specific heat C(T) measurements. Superconductivity is of bulk nature because of the jump at T-c from specific heat measurements. The Sommerfeld constant gamma and Debye temperature Theta(D) are estimated to be 9.6 mJ/(mol .K-2) and 450 K. The upper critical filed mu H-0(c2)(0) is estimated to be 0.825 T obtained from rho(T) in several magnetic fields.

DOI： 10.1016/j.physb.2020.412149

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Coexistence of localized and heavy itinerant states in antiferromagnetic CePtGe2

Tomohito Nakano, Shoma Onuma, Naoya Takeda, Klara Uhlirova, Jan Proklesky, Vladimir Sechovsky, Jun Gouchi, Yoshiya Uwatoko

PHYSICAL REVIEW B 100 ( 3 ) 2019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

Two conflicting ground states, i.e., an antiferromagnetic ground state at 3.8K and aferromagnetic ground state at 5.1 K, have been reported for CePtGe2, which has two nonequivalent crystallographic Ce sites. In this study, we have prepared polycrystalline and single-crystalline CePtGe2 samples and measured their magnetization, specific heat, resistivity, and Seebeck coefficient. The observed bend in resistivity, peak in magnetic susceptibility, and lambda-type anomaly in specific heat at T-N = 3.8K and the metamagnetic transition in this CePtGe2 suggest antiferromagnetism at low temperatures. No evidence of ferromagnetic order was found in the studied temperature range, indicating possible crystal polymorphism with ferromagnetic character. The large susceptibility around TN and the Schottky-type specific heat indicate a well-localized f -electron state. However, the large residual gamma and X(0) indicate an itinerant heavy f -electron state. These findings suggest the coexistence of localized and heavy itinerant states corresponding to f electrons at the two Ce sites in this antiferromagnetic CePtGe2. The field dependence of magnetization indicates a sudden increase in magnetization at weak magnetic fields (similar to 0.2T), followed by a plateau at fields above 0.2 T, resulting in a possible different polarized metamagnetic state via interaction between localized and itinerant f electrons.

DOI： 10.1103/PhysRevB.100.035107

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単斜晶EuPdGeの単結晶育成と基礎物性

神戸繭, 永井維, 齋藤達也, 山内直也, 畠山淳, 皆川絢乃, 野本隆宏, 加瀬直樹, 中野智仁, 武田直也

日本物理学会講演概要集 74.2 1928 - 1928 2019年

CePtGe2の圧力下における低温物性II

郷地順, 大沼翔馬, 中野智仁, 武田直也, 上床美也

日本物理学会講演概要集 74.1 1978 - 1978 2019年

Fundamental properties of a new samarium compound SmPtSi2 査読

Shuto Yamaguchi, Eisuke Takahashi, Naoki Kase, Tomohito Nakano, Naoya Takeda, Kazuyuki Matsubayashi, Yoshiya Uwatoko

Physica B: Condensed Matter 536 297 - 299 2018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 B.V.

We have discovered a new orthorhombic ternary compound SmPtSi2. We succeeded in growing a single crystal of SmPtSi2
prepared a polycrystalline sample of this compound, and measured their susceptibility, specific heat, and resistivity. The temperature dependence of susceptibility of the polycrystalline sample is close to that of Sm3+ at high temperatures, and its specific heat shows anomalies at TH = 8.6 K and TL = 5.6 K. The resistivity of a single crystal of SmPtSi2 shows a hump-type anomaly just below TH and a sudden decrease at TL, indicating that these anomalies are intrinsic and that SmPtSi2 exhibits a two-step transition.

DOI： 10.1016/j.physb.2017.10.028

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Thermal expansion and magnetostriction of clathrate compound Pr3Pd20Ge6 査読

K.Matsumoto, Y.Sekiguchi, O.Iwakami, T.Ono, S.Abe, G.Ano, M.Akatsu, K.Mitsumoto, Y.Nemoto, T.Goto, N.Takeda, H.Kitazawa

J.Phys.:Conf. Series 969 012120-1 - 012120-6 2018年4月

Superfluidity of 4He in dense aerogel studied using quartz tuning fork 査読

K Matsumoto, Y Sekiguchi, O Iwakami, T Ono, S Abe, G Ano, M Akatsu, K Mitsumoto, Y Nemoto, T Goto, N Takeda, H Kitazawa

J. Phys.: Conf. Ser. 969 12019 2018年

単結晶α-Mnの試料育成と圧力下物性

戸丸有沙, 福原慶, 中野智仁, 武田直也, 雨海有佑, 村山茂幸

日本物理学会講演概要集 73 ( 0 ) 541 - 541 2018年

1T-Ta(S1-xSex)の熱電特性

荒木遼太, 松本絋祐, 中野智仁, 武田直也

日本物理学会講演概要集 73 ( 0 ) 1568 - 1568 2018年

空間反転対称性の破れた結晶構造をもつBaTSi (T = Pd, Pt)の基礎物性

木村優治, 細道正春, 中野智仁, 武田直也

日本物理学会講演概要集 73 ( 0 ) 1187 - 1187 2018年

カゴ状物質Lu5T6Sn18 (T = Co, Ir)における異方的超伝導

渡邉和平, 穴田泰士, 中野智仁, 武田直也

日本物理学会講演概要集 73 ( 0 ) 1188 - 1188 2018年

CePtGe2の圧力下における低温物性

郷地順, 大沼翔馬, 中野智仁, 武田直也, 上床美也

日本物理学会講演概要集 73 ( 0 ) 1518 - 1518 2018年

遷移金属酸化物BaIrO3の単結晶試料作成と物性

土門優志, 川井賢吾, 中野智仁, 武田直也

日本物理学会講演概要集 73 ( 0 ) 609 - 609 2018年

SmPtSi2の試料作成と基礎物性

山口嵩人, 高橋英亮, 中野智仁, 武田直也, 松林和幸, 上床美也, Uhlirova K., Pronkleska J., Sechovsky V.

日本物理学会講演概要集 73 ( 0 ) 1714 - 1714 2018年

Superconducting gap symmetry of the BiS2-based superconductor LaO0.5F0.5BiSSe elucidated through specific heat measurements 査読

Naoki Kase, Yusuke Terui, Tomohito Nakano, Naoya Takeda

PHYSICAL REVIEW B 96 ( 21 ) 2017年12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

In this study, the superconducting gap symmetry of LaO0.5F0.5BiSSe is elucidated through specific heat measurements with one single crystal of LaO0.5F0.5BiSSe. A clear jump is observed at 3.95 K in LaO0.5F0.5BiSSe, suggesting bulk superconductivity. From specific heat measurements, Delta C-e/gamma T-c and 2 Delta(0)/k(B)T(c) are obtained as 2.31 and 4.5. These values indicate strong electron-phonon coupling superconductivity. The temperature (T) and magnetic-field (H) dependence of the electronic specific heat C-e(T, H) suggests that superconductivity is fully gapped. Our handmade system successfully elucidates superconducting gap symmetry of the BiS2-based compound with a small single crystal.

DOI： 10.1103/PhysRevB.96.214506

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Upper critical field of the single crystal La(O,F)BiSe2 査読

Y.Terui, N.Kase, T.Nakano, N.Takeda

J.Phys.: Conf.Series 871 012005-1 - 012005-5 2017年7月

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