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論文

Magnetic field induced triple-$$q$$ magnetic order in trillium lattice antiferromagnet EuPtSi studied by resonant X-ray scattering

田端 千紘*; 松村 武*; 中尾 裕則*; 道村 真司*; 垣花 将司*; 稲見 俊哉*; 金子 耕士; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

Journal of the Physical Society of Japan, 88(9), p.093704_1 - 093704_5, 2019/09

The magnetic order in the magnetic-fild-induced so-called A phase of cubic chiral antiferromagnet EuPtSi was investigated by resonant X-ray scattering (RXS) near the Eu $$L_{2}$$ edge. The high flux RXS signal under the magnetic field applied along [111] revealed the first and second order satellite magnetic reflections, indicating that the A phase is a triple-$$q$$ magnetic ordered state that is described by three propagation vectors lying in the plane normal to the magnetic field direction; $$q_1$$, $$q_2$$, and $$q_3$$. With the high resolution in the reciprocal space achieved in the RXS measurement, it is suggested that the triple-$$q$$ order strongly couples with the underlying crystal lattice. The triple-$$q$$ magnetic order is discussed in the context of a magnetic skyrmion lattice on which the geometrical frustration may play a crucial role.

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

Unique helical magnetic order and field-induced phase in trillium lattice antiferromagnet EuPtSi

金子 耕士; Frontzek, M. D.*; 松田 雅昌*; 中尾 朗子*; 宗像 孝司*; 大原 高志; 垣花 将司*; 芳賀 芳範; 辺土 正人*; 仲間 隆男*; et al.

Journal of the Physical Society of Japan, 88, p.013702_1 - 013702_5, 2019/01

 被引用回数:1 パーセンタイル:14.05(Physics, Multidisciplinary)

Magnetic transitions in chiral antiferromagnet EuPtSi were investigated by means of single crystal neutron diffraction. In the ground state, magnetic peaks emerge at positions represented by $$q_{1}$$=$$(0.2, 0.3, 0)$$. Upon heating, an additional magnetic peak splitting around 2.5 K was uncovered, indicating a presence of a first-order transition with $$q^*_{1}$$=$$(0.2, 0.3, {delta})$$. An half-polarized neutron scattering for polarization parallel to Q reveled that polarization antiparallel to Q has stronger intensity in both magnetic phases. This feature clarifies single chiral character of helical structure with moments normal to the ordering vector in both ordered states. Under vertical magnetic field along [1,1,1] in the $$A$$ phase, magnetic peaks form hexagonal patterns in the equatorial scattering plane around nuclear. An ordering vector $$q_{A}$$ of the $$A$$-phase has the similar size in the periodicity to $$q_{1}$$, and could be a hallmark of a formation of skyrmion lattice in EuPtSi.

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 $$x$$.

論文

Magnetic structure of divalent europium compound EuGa$$_{4}$$ studied by single-crystal time-of-flight neutron diffraction

川崎 卓郎; 金子 耕士; 仲村 愛*; 阿曽 尚文*; 辺土 正人*; 仲間 隆男*; 大原 高志; 鬼柳 亮嗣; 及川 健一; 田村 格良; et al.

Journal of the Physical Society of Japan, 85(11), p.114711_1 - 114711_5, 2016/11

 パーセンタイル:100(Physics, Multidisciplinary)

The magnetic structure of the intermetallic compound EuGa$$_{4}$$ was investigated using single-crystal neutron diffraction with TOF Laue technique on the new diffractometer SENJU at MLF of J-PARC. Despite of the high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections appeared at $$h + k + l$$ $$neq$$ 2$$n$$ below 16 K, indicating that the ordering vector is $$q$$ = (0, 0, 0). The continuous evolution of the magnetic reflection intensity below T$$_{N}$$ follows a squared Brillouin function for $$S$$ = 7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa$$_{4}$$ revealed that a nearly full magnetic moment of 6.4 $$mu$$B of Eu lies within the basal plane of the lattice.

論文

Electronic structure of EuAl$$_4$$ studied by photoelectron spectroscopy

小畠 雅明; 藤森 伸一; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 小林 啓介*; 山上 浩志; 仲村 愛*; 辺土 正人*; 仲間 隆男*; et al.

Journal of the Physical Society of Japan, 85(9), p.094703_1 - 094703_6, 2016/09

 被引用回数:4 パーセンタイル:44.55(Physics, Multidisciplinary)

The electronic structure of a divalent $$mathrm{Eu}$$ compound EuAl$$_4$$, which shows the charge density wave transition at $$T_{mathrm{CDW}} = 140~mathrm{K}$$, was studied by the hard X-ray angle-integrated photoelectron spectroscopy (HAXPES) and the soft X-ray angle resolved photoelectron spectroscopy (ARPES). The valence band and core-level spectra obtained by the HAXPES are consistent with the divalent nature of Eu atoms in EuAl$$_4$$. Furthermore, the Fermi surface as well as the band structure in the vicinity of the Fermi Energy ($$E_{rm F}$$) of EuAl$$_4$$ are very similar to those of its isostructural divalent $$mathrm{Sr}$$ compound SrAl$$_4$$, which does not have $$4f$$ electrons. These suggest that Eu atoms are divalent in EuAl$$_4$$, and $$4f$$ electrons are completely localized with $$mathrm{Eu}~4f^7$$ electronic configuration in the ground state. The ARPES spectra measured along the $$Gamma$$-$$(Sigma)$$-Z high-symmetry line did not show significant temperature dependences above and below $$T_{mathrm{CDW}}$$ within the energy resolution of $$80-90~mathrm{meV}$$. Moreover, the Fermi surface mapping along the $$k_z$$ direction showed that both of EuAl$$_4$$ and SrAl$$_4$$ have highly three-dimensional electronic structures, suggesting that the nesting of Fermi surface is not straightforward. The Fermi surface and band structure of SrAl$$_4$$ were well explained by the band-structure calculation based on the local density approximation.

論文

Superconducting and Fermi surface properties of single crystal Zr$$_2$$Co

照屋 淳志*; 垣花 将司*; 竹内 徹也*; 青木 大*; 本多 史憲*; 仲村 愛*; 芳賀 芳範; 松林 和幸*; 上床 美也*; 播磨 尚朝*; et al.

Journal of the Physical Society of Japan, 85(3), p.034706_1 - 034706_10, 2016/03

 パーセンタイル:100(Physics, Multidisciplinary)

Superconducting characteristics and Fermi surfaces of Zr$$_2$$Co are experimentally studied on a single crystal sample grown by Bridgman technique. Thermodynamic quantities in the superconducting state such as specific heat and magnetization show deviation from a single-gap the BCS model and can be attributed on the band structure with the dominant contribution of Zr-4$$d$$ and Co-3$$d$$ components.

論文

Split Fermi surface properties in Ulmannite NiSbS and PdBiSe with the cubic chiral crystal structure

垣花 将司*; 照屋 淳志*; 西村 憲吾*; 仲村 愛*; 竹内 徹也*; 芳賀 芳範; 播磨 尚朝*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦

Journal of the Physical Society of Japan, 84(9), p.094711_1 - 094711_8, 2015/09

 被引用回数:8 パーセンタイル:31.29(Physics, Multidisciplinary)

Fermi surface properties of illuminate NiSbS and PbBiSe have been clarified by de Haas-van Alphen effect, resistivity and specific heat measurements. Fermi surfaces were found to split into two, reflecting the non-centrosymmetric crystal structure. The splitting energies have been estimated experimentally. Those are originated from spin-orbit interactions.

論文

Characteristic fermi surface properties of V$$_2$$Ga$$_5$$, CoGa$$_3$$, TiGa$$_3$$, ZrGa$$_3$$, and ZrAl$$_3$$ with different tetragonal structures

照屋 淳志*; 竹田 政貴*; 仲村 愛*; 播磨 尚朝*; 芳賀 芳範; 内間 清春*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*

Journal of the Physical Society of Japan, 84(5), p.054703_1 - 054703_15, 2015/05

 被引用回数:3 パーセンタイル:58.15(Physics, Multidisciplinary)

A series of metallic compounds with the tetragonal symmetry are investigated to reveal the relationship between the structural dimensionality and the electronic structure. By combining the de Haas-van Alphen experiments and band structure calculations, a flat one-dimensional Fermi surface is revealed in V$$_2$$Ga$$_5$$ which is characterized by a chain like arrangement of atoms. On the other hand, Co$$_3$$Ga with the nearly cubic symmetry has pyramidal Fermi surfaces with flat {111} planes, similar to Ni$$_3$$Ga with the ideal cubic structure.

論文

Unique Fermi surface and emergence of charge density wave in EuGa$$_4$$ and EuAl$$_4$$

仲村 愛*; 平仲 裕一*; 辺土 正人*; 仲間 隆男*; 三浦 泰直*; 堤 泰樹*; 森 晶宣*; 石田 一裕*; 三田村 勝哉*; 広瀬 雄介*; et al.

JPS Conference Proceedings (Internet), 3, p.011012_1 - 011012_6, 2014/06

Two europium compounds with the same structure EuGa$$_4$$ and EuAl$$_4$$ have been investigated. The Fermi surfaces revealed experimentally show a peculiar feature: flat Fermi surface sheets appear parallel to the tetragonal [110] planes. Reflecting this, a charge density wave transition due to the nesting of Fermi surface sheets has been observed in EuAl$$_4$$.

論文

Single crystal neutron diffraction study of high neutron absorbing compound EuGa$$_{4}$$

川崎 卓郎; 金子 耕士; 阿曽 尚文*; 仲村 愛*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*; 大原 高志; 鬼柳 亮嗣; 及川 健一; et al.

JPS Conference Proceedings (Internet), 1, p.014009_1 - 014009_4, 2014/03

Single crystal neutron diffraction measurement of EuGa$$_{4}$$ has been carried out using time-of-flight single crystal neutron diffractometer SENJU at BL18 in MLF/J-PARC. In spite of extremely high neutron absorption of natural Eu, significant numbers of Bragg reflection were observed. Lattice parameters and Bravais lattice at above $$T_mathrm{N}$$ (=15 K) obtained from the positions and systematic extinction of the reflections were well agreed with the result of single crystal X-ray diffraction. Further, magnetic reflections were clearly observed at below $$T_mathrm{N}$$ at the positions of forbidden reflections of body-centered lattice of EuGa$$_{4}$$. An antiferromagnetic structure with the propagation vector $$q$$ = 0 was clarified.

論文

Fermi surface and magnetic properties of antiferromagnet EuBi$$_3$$

仲村 愛*; 平仲 裕一*; 辺土 正人*; 仲間 隆男*; 立津 慶幸*; 眞榮平 孝裕*; 三浦 泰直*; 森 晶宣*; 堤 泰樹*; 広瀬 雄介*; et al.

Journal of the Physical Society of Japan, 82(12), p.124708_1 - 124708_6, 2013/12

 被引用回数:13 パーセンタイル:28.22(Physics, Multidisciplinary)

Fermi surfaces and magnetic properties of an antiferromagnet EuBi$$_3$$ were investigated on a flux-grown single crystal. A critical magnetic field of 225 kOe where the magnetic moments are forced to align ferromagnetically was well explained by the magnetic exchange interaction based on a two-sublattice model. The Fermi surface characteristics are in agreement with the theoretical prediction indicating a fully magnetic divalent state in Eu atoms.

論文

Magnetic and Fermi surface properties of EuGa$$_4$$

仲村 愛*; 平仲 裕一*; 辺土 正人*; 仲間 隆男*; 三浦 泰直*; 堤 泰樹*; 森 晶宣*; 石田 一裕*; 三田村 勝哉*; 広瀬 雄介*; et al.

Journal of the Physical Society of Japan, 82(10), p.104703_1 - 104703_10, 2013/10

 被引用回数:23 パーセンタイル:16.99(Physics, Multidisciplinary)

High quality single crystals of EuGa$$_4$$ have been grown from Ga flux. Electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, thermoelectric power and de Haas-van Alphen effect were investigated. Antiferromagnetic transition due to divalent Eu atoms were observed at 16.5 K. A charge density wave transition was also found under high pressure accompanied by a Fermi surface reconstruction. These observations were fully accounted for by the Fermi surface topology and corresponding band calculations.

口頭

単結晶中性子回折法による高い中性子吸収を示すEuGa$$_{4}$$の磁気構造解析

川崎 卓郎; 金子 耕士; 阿曽 尚文*; 仲村 愛*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*; 大原 高志; 鬼柳 亮嗣; 及川 健一; et al.

no journal, , 

物質の磁気的性質を調べる手段として、中性子回折を用いた磁気構造解析は基礎的かつ強力である。パルス中性子回折では短波長の中性子を利用できるためEuやDyのように中性子の吸収が大きな元素を含む物質の構造研究に有効であることが期待される。EuGa$$_{4}$$は豊富な物性を示すことで知られるEuT$$_{2}$$X$$_{2}$$で表される122化合物と呼ばれる一連の物質の母物質であると考えられており、15Kで反強磁性的な相転移を示すことが報告されているが、詳細な磁気構造は明らかになっていない。今回、J-PARC/MLFの単結晶中性子回折装置SENJUを使用して、Euを吸収の小さい同位体に置換していないEuGa$$_{4}$$単結晶の磁気構造解析を試みたので、結果を報告する。

口頭

軟X線角度分解光電子分光によるEuAl$$_4$$の電子状態

小畠 雅明; 藤森 伸一; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 小林 啓介*; 山上 浩志; 仲村 愛*; 辺土 正人*; 仲間 隆男*; et al.

no journal, , 

体心正方晶(BaAl$$_4$$型)を持つEuAl$$_4$$は、T=15K付近で反強磁性体で、T=140Kでフェルミ面のネスティング効果による電荷密度波(CDW)を示唆する肩構造が電気抵抗に現れる興味深い物性をもつ物質である。この物性を理解するためにEuAl$$_4$$のバンド構造とフェルミ面に関する情報を得ることは物理的に重要である。そこで、本研究では、EuAl$$_4$$のバンド構造とフェルミ面の形状を実験的に決めることを目的とし、原子力機構専用ビームラインBL23SU(SPring-8)で軟X線角度分解光電子分光(SX-ARPES)実験を行った。その結果から、EuAl$$_4$$のEuは、2価であることが分かった。また、この物質の4${it f}$バンドはフェルミ準位以下の約1eVの所に存在した。そのため、フェルミ面は4${it f}$バンド以外の価電子からできていると考えられる。そこで、4${it f}$電子の価電子帯への寄与をより明確にするために、同じ結晶構造で${it f}$電子をもたないSrAl$$_4$$の電子状態と比較することが有効と考え、両者の電子構造について比較を行った。両者のフェルミ付近のバンド構造やフェルミ面の形状は、類似することが分かった。講演では、バンド計算と比較して、この化合物の電子状態について報告する。

口頭

Contrasting magnetic ground state in isoelectronic compound Eu$$X_4$$ ($$X$$ = Al, Ga)

金子 耕士; 川崎 卓郎; 仲村 愛*; 茂吉 武人*; 宗像 孝司*; 中尾 朗子*; 花島 隆泰*; 鬼柳 亮嗣; 大原 高志; 及川 健一; et al.

no journal, , 

As a consequence of strong coupling among charge, magnetic and orbital degrees of freedom, a variety of attractive physical properties comes out in Eu compounds. In Eu$$X_4$$ ($$X$$ = Al, Ga) with the BaAl$$_{4}$$-type structure, Eu ions are divalent and, hence, carry magnetism with S = 7/2. These isoelectronic compounds exhibit contrasting magnetic properties. In order to reveal respective ground states from a microscopic point of view, single crystal neutron diffraction experiments were carried out on SENJU at BL18 in MLF. Superlattice peaks were successfully observed in both compounds. The magnetic ground state of EuGa$$_4$$ can be described by the commensurate vector. On the other hand, the ground state in EuAl$$_4$$ is characterized with the long periodic magnetic structure. This study reveals that, in addition to the transition sequence, the ground state magnetic structures are also different between these compounds.

口頭

Eu$$X_4$$($$X$$=Al, Ga)で実現する対照的な基底状態

金子 耕士; 川崎 卓郎; 仲村 愛*; 茂吉 武人*; 宗像 孝司*; 中尾 朗子*; 花島 隆泰*; 鬼柳 亮嗣; 大原 高志; 及川 健一; et al.

no journal, , 

価数揺動など多彩な物性を示すEuT$$_2X_2$$化合物の母物質であるEuX$$_4$$($$X$$=Al,Ga)では、Euは2価の電子状態を取り、S=7/2で記述される物性を示す。EuGa$$_4$$では、T$$_N$$=16Kの反強磁性転移を示すのに対し、EuAl$$_4$$は、基底状態に至るまでに5つの転移点を持つ、複雑な物性を示す。この両者における各転移の詳細な描像に関して、単結晶中性子回折を用いて明らかにしたので、報告する。

口頭

単結晶中性子回折法を用いた高い中性子吸収を示すEuX$$_{4}$$(X=Al,Ga)の磁気構造の研究

川崎 卓郎; 金子 耕士; 阿曽 尚文*; 仲村 愛*; 辺土 正人*; 仲間 隆男*; 大貫 惇睦*; 茂吉 武人*; 中尾 朗子*; 花島 隆泰*; et al.

no journal, , 

単結晶中性子回折法による磁気反射の観測は物質の磁気的性質を調べるための最も基礎的かつ強力な手法であるが、Eu, Gd, Sm, Dyなどの希土類元素は中性子の吸収が非常に大きく、これらの元素を含む化合物の中性子回折による磁気構造の研究例は限られている。一方、吸収の影響が小さい短波長中性子を利用可能な白色中性子と、大面積検出器を組み合わせたパルス中性子回折装置を用いることで、吸収の大きな希土類元素を含む物質の磁気構造を効率的に調べられることが期待できる。我々はEuを含み、同一な結晶構造と原子価をもちながらも異なる磁気転移を示す二つの物質、EuGa$$_{4}$$とEuAl$$_{4}$$に注目し、J-PARC MLF BL18に設置された単結晶中性子回折装置SENJUを用いて中性子回折測定を実施した。その結果、これらの物質において異なる磁気的秩序状態を示す磁気反射を観測し、EuGa$$_{4}$$は4Kにおいて伝搬ベクトルq=(0 0 0)の反強磁性的構造であり、EuAl$$_{4}$$は不整合的な磁気構造となっていることがわかった。

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