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論文

Electronic states of EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$ 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

We have carried out angle-integrated photoemission spectroscopy (AIPES) and angle-resolved photoemission spectroscopy (ARPES) experiments using soft X-rays on single crystals of EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$ grown by the Bridgman method to investigate their electronic structures. The AIPES results showed that the Eu ions in EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$ 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 EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$ were studied by ARPES measurements. We found that the band structures near the Fermi level and Fermi surfaces of EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$ are very different from each other and are well reproduced by the band structure calculations based on density-functional theory for SrCu$$_2$$Ge$$_2$$ and YCu$$_2$$Si$$_2$$. This suggests that a charge transfer from the localized 4$$f$$ states into the valence bands is responsible for the difference in the electronic states between EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$.

論文

Anomalous ferromagnetic ordering in EuCuP

伊覇 航*; 垣花 将司*; 松田 進弥*; 本多 史憲*; 芳賀 芳範; 竹内 徹也*; 中島 美帆*; 天児 寧*; 郷地 順*; 上床 美也*; et al.

Journal of Alloys and Compounds, 788, p.361 - 366, 2019/06

Ferromagnetic ordering of EuCuP is investigated on a single crystal sample grown from tin flux. Application of hydrostatic pressure up to 8 GPa stabilizes ferromagnetic ordering, suggesting divalent Eu is stable. The Hall effect and resistivity measurements show that EuCuP is a low-carrier ferromagnetic metal with a characteristic resistivity cusp appearing at the ferromagnetic transition temperature.

論文

Effects of magnetic field and pressure on the valence-fluctuating antiferromagnetic compound EuPt$$_2$$Si$$_2$$

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

 被引用回数:2 パーセンタイル:29.91(Physics, Multidisciplinary)

Effects of magnetic field and pressure on the Kondo-like behavior in the valence-fluctuating antiferromagnetic compound EuPt$$_2$$Si$$_2$$ were studied using single-crystalline samples. Anomalous features in EuPt$$_2$$Si$$_2$$ are due to valence fluctuation and/or valence change of the Eu ions at low temperatures.

論文

Electronic states in EuCu$$_2$$(Ge$$_{1-x}$$Si$$_x$$)$$_2$$ based on the doniach phase diagram

伊覇 航*; 屋良 朝之*; 安次富 洋介*; 垣花 将司*; 竹内 徹也*; 本多 史憲*; 仲村 愛*; 青木 大*; 郷地 順*; 上床 美也*; et al.

Journal of the Physical Society of Japan, 87(6), p.064706_1 - 064706_14, 2018/06

 被引用回数:2 パーセンタイル:29.91(Physics, Multidisciplinary)

We succeeded in growing single crystals of the series of EuCu$$_2$$(Ge$$_{1-x}$$Si$$_x$$)$$_2$$ compounds.Physical property measurements demonstrate a maximum of the antiferromagnetic transition temperature appears at $$x = 0.5$$. Antiferromagnetism then disappears around $$x = 0.7$$ followed by a heavy-fermion formation at higher concentrations. These observations follow the Doniach phase diagram as a function of $$x$$.

口頭

軟X線角度分解光電子分光法によるEuCu$$_2$$Ge$$_2$$とEuCu$$_2$$Si$$_2$$の電子状態の研究

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*

no journal, , 

EuCu$$_2$$(Ge$$_{1-x}$$Si$$_x$$)$$_2$$はSi濃度を変化させることでEuの価数が変化し、磁気的な基底状態をもつEu$$^{2+}$$(x=0)の状態から非磁性のEu$$^{3+}$$(x=1)の状態に移り変わる。また、磁気秩序が消失するx=0.65近傍では重い電子状態が発現することが知られている。本講演では両端のEuCu$$_2$$Ge$$_2$$とEuCu$$_2$$Si$$_2$$に対して実施した角度分解光電子分光測定の結果について紹介し、Siドープによって引き起こされる電子状態の変化について議論する。

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