23の空間群に属する化合物および関連する化合物の結晶構造について

垣花 将司*; 竹内 徹也*; 芳賀 芳範; 播磨 尚朝*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

固体物理, 55(10), p.505 - 514, 2020/10

立方晶キラル構造に属する磁性体が示す特異な磁気相が注目されている。代表的な物質MnSi(空間群23)および関連物質の構造の特徴を分類するとともに、一見複雑に見える結晶構造を安定化させる要因について考察する。

Electronic structure of trivalent compound EuPd studied by soft X-ray angle-resolved photoemission spectroscopy

川崎 郁斗; 小畠 雅明; 藤森 伸一; 竹田 幸治; 山上 浩志; 仲村 愛*; 伊覇 航*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

Journal of the Physical Society of Japan, 89(4), p.044704_1 - 044704_6, 2020/04

https://doi.org/10.7566/JPSJ.89.044704

EuPd is a rare Eu-based compound, whose Eu ions are in a trivalent state. The electronic structure of EuPd was investigated by angle-resolved photoemission spectroscopy (ARPES) using soft X rays. Eu components arising from the 4f final state multiplet were clearly observed in the valence spectra, and no Eu components were observed within an experimental accuracy, confirming a robust Eu state. The band structure and Fermi surfaces revealed by ARPES measurements were compared to the band structure calculations based on the density-functional theory for LaPd andYPd. We found that the calculation for LaPd provides a better description for our ARPES results. The effective electron masses estimated from the ARPES spectra near the Fermi level are in good agreement with the corresponding cyclotron effective masses in previous de Haas-van Alphen experiments.

Spin glass behavior in EuCuSi single crystal grown by the flux method

竹内 徹也*; 芳賀 芳範; 谷口 年史*; 伊覇 航*; 安次富 洋介*; 屋良 朝之*; 木田 孝則*; 田原 大夢*; 萩原 政幸*; 中島 美帆*; et al.

Journal of the Physical Society of Japan, 89(3), p.034705_1 - 034705_15, 2020/03

https://doi.org/10.7566/JPSJ.89.034705

Single crystals of EuCuSi have been grown by the flux method and Bridgman method. The Eu ions of the Bridgman-grown crystal are nearly trivalent and fluctuate depending on the temperature. On the other hand, the Eu ions of flux-grown sample are divalent and thermally stable and show spin-glass behavior at low temperatures. Crystallographic analyses identified random replacement of Cu sites by Si only for the flux-grown samples. Such structural randomness leads to spin-glass features.

4電子系化合物EuPtSiにおける磁気スキルミオン

金子 耕士; 垣花 将司*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

固体物理, 54(12), p.757 - 766, 2019/12

MnSiと同じ空間群に属する4電子系化合物EuPtSiについて、磁気特性を調べた。単結晶中性子回折実験の結果、MnSiとEuPtSiの磁気構造に多くの共通点を見出した。この結果は、EuPtSiが4電子系で初めて磁気スキルミオン格子を示す物質であることを示している。

Electronic states of EuCuGe and EuCuSi studied by soft X-ray photoemission spectroscopy

川崎 郁斗; 藤森 伸一; 竹田 幸治; 山上 浩志; 伊覇 航*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

Physical Review B, 100(3), p.035111_1 - 035111_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.035111

We have carried out angle-integrated photoemission spectroscopy (AIPES) and angle-resolved photoemission spectroscopy (ARPES) experiments using soft X-rays on single crystals of EuCuGe and EuCuSi grown by the Bridgman method to investigate their electronic structures. The AIPES results showed that the Eu ions in EuCuGe and EuCuSi are in a divalent state and a nearly trivalent state, respectively, in accord with the previously reported magnetic properties. The three-dimensional band structures and shapes of the Fermi surfaces of EuCuGe and EuCuSi were studied by ARPES measurements. We found that the band structures near the Fermi level and Fermi surfaces of EuCuGe and EuCuSi are very different from each other and are well reproduced by the band structure calculations based on density-functional theory for SrCuGe and YCuSi. This suggests that a charge transfer from the localized 4 states into the valence bands is responsible for the difference in the electronic states between EuCuGe and EuCuSi.

Evidence for weak spin-orbit interaction experienced by Cooper pairs in the spin-triplet superconductor UPt; Pt-NMR study

青山 泰介*; 小手川 恒*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦*; 藤 秀樹*

Journal of the Physical Society of Japan, 88(6), p.064706_1 - 064706_7, 2019/06

https://doi.org/10.7566/JPSJ.88.064706

Pt-NMR measurements under magnetic field () parallel to the -axis in the vicinity of the upper critical field have been carried out on the heavy-fermion superconductor UPt. The quasiparticle spin susceptibility was obtained from the measurements. The field dependence of the susceptibility suggests that the -vector freely rotates in magnetic field. It is therefore concluded that spin-orbit interaction, which confines the direction of the -vector with respect to the crystal axis, is weak in UPt.

Manifestation of electron correlation effect in 5 states of uranium compounds revealed by 4-5 resonant photoelectron spectroscopy

藤森 伸一; 小畠 雅明; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*

Physical Review B, 99(3), p.035109_1 - 035109_5, 2019/01

https://doi.org/10.1103/PhysRevB.99.035109

In the present study, we have elucidated the nature of the electron correlation effect in uranium compounds by imaging the partial density of states (pDOS) of typical itinerant, localized, and heavy fermion uranium compounds by using the 4-5 resonant photoemission spectroscopy. Obtained pDOS exhibit a systematic trend depending on the physical properties of compounds: Although the coherent peak at the Fermi level can be explained by the band-structure calculation, an incoherent peak emerges on the higher binding energy side () in the cases of localized and heavy fermion compounds. The intensity and energy position of the incoherent peak is increased and shifted to a higher binding energy as the localization of the state increases. These behaviors are consistent with the prediction of the Mott metal-insulator transition, suggesting that the Hubbard- type mechanism takes an essential role in the electronic structure of actinide materials.

Effects of magnetic field and pressure on the valence-fluctuating antiferromagnetic compound EuPtSi

竹内 徹也*; 屋良 朝之*; 安次富 洋介*; 伊覇 航*; 垣花 将司*; 中島 美帆*; 天児 寧*; 本多 史憲*; 本間 佳哉*; 青木 大*; et al.

Journal of the Physical Society of Japan, 87(7), p.074709_1 - 074709_14, 2018/07

https://doi.org/10.7566/JPSJ.87.074709

Effects of magnetic field and pressure on the Kondo-like behavior in the valence-fluctuating antiferromagnetic compound EuPtSi were studied using single-crystalline samples. Anomalous features in EuPtSi are due to valence fluctuation and/or valence change of the Eu ions at low temperatures.

Element-specific observation of the ferromagnetic ordering process in UCoAl via soft X-ray magnetic circular dichroism

竹田 幸治; 斎藤 祐児; 岡根 哲夫; 山上 浩志; 松田 達磨*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦*

Physical Review B, 97(18), p.184414_1 - 184414_7, 2018/05

AA2018-0316.pdf:0.62MB

https://doi.org/10.1103/PhysRevB.97.184414

We have performed soft X-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U 4-5 () and Co 2-3 () absorption edges in order to investigate the magnetic properties of the U 5 and Co 3 electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co 3 electrons is unusually large. Through the systematic temperature ()- and magnetic field ()-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of and (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was observed clearly under 15 K at . The value of the and its -dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings show clearly that the role of the Co 3 electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.

Electronic structures of U (=Al, Ga, and In) studied by photoelectron spectroscopy

藤森 伸一; 小畠 雅明; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*

Physical Review B, 96(11), p.115126_1 - 115126_10, 2017/09

https://doi.org/10.1103/PhysRevB.96.115126

The electronic structures of U (=Al, Ga, and In) were studied by photoelectron spectroscopy to understand the the relationship between their electronic structure and magnetic properties. The band structures and Fermi surfaces of UAl and UGa were revealed experimentally by angle-resolved photoelectron spectroscopy (ARPES), and they were compared with the result of band structure calculations. The topologies of the Fermi surfaces and the band structures of UAl and UGa were explained reasonably well by the calculation, although bands near the Fermi level () were renormalized owing to the finite electron correlation effect. The topologies of the Fermi surfaces of UAl and UGa are very similar to each other, except for some minor differences. Such minor differences in their Fermi surface or electron correlation effect might take an essential role in their magnetism.