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
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 =. Upon heating, an additional magnetic peak splitting around 2.5 K was uncovered, indicating a presence of a first-order transition with =. 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 phase, magnetic peaks form hexagonal patterns in the equatorial scattering plane around nuclear. An ordering vector of the -phase has the similar size in the periodicity to , and could be a hallmark of a formation of skyrmion lattice in EuPtSi.
立岩 尚之; Pospil, J.*; 芳賀 芳範; 酒井 宏典; 松田 達磨*; 山本 悦嗣
Progress in Nuclear Science and Technology (Internet), 5, p.104 - 107, 2018/12
ウラン系強磁性超伝導物質UGe, URhGe, UCoGeについて盛んに研究が行われてきた。最近、我々は69個のウラン化合物、7個のネプツニウム化合物、4個のプルトニウム化合物について、スピンゆらぎ理論の適用性を検討した。その結果、アクチノイド5電子の遍歴性を示唆する結果が得られた。会議では全強磁性化合物の解析結果と、UGeのスピンのゆらぎパラーメーターの圧力依存を議論する。
目時 直人; 芳賀 芳範; 山本 悦嗣; 松田 雅昌*
Journal of the Physical Society of Japan, 87(11), p.114712_1 - 114712_9, 2018/11
竹内 哲也*; 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
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.
Pospil, J.*; 芳賀 芳範; 小濱 芳允*; 三宅 厚志*; 神戸 振作; 立岩 尚之; Valika, M.*; Proschek, P.*; Prokleka, J.*; Sechovsk, V.*; et al.
Physical Review B, 98(1), p.014430_1 - 014430_7, 2018/07
The metamagnetic transition between the antiferromagnetic and paramagnetic state in UIrGe has been studied at various temperatures by magnetization, heat capacity, and magnetocaloric effect measurements on a single crystal in static and pulsed magnetic fields applied along the orthorhombic axis. The first-order transition is accompanied by a dramatic increase of the Sommerfeld coefficient. A tentative scenario explaining these anomalies by antiferromagnetic correlations or short-range order in the paramagnetic state is discussed.
神戸 振作; 徳永 陽; 酒井 宏典; 服部 泰佑; 比嘉 野乃花; 松田 達磨*; 芳賀 芳範; Walstedt, R. E.*; 播磨 尚朝*
Physical Review B, 97(23), p.235142_1 - 235142_10, 2018/06
We report Si and Ru NMR measurements on high-quality, single-crystal URuSi samples with a residual resistivity ratio RRR70. Our results show that the Si and Ru sites exhibit 4-fold electronic symmetry around the -axis in the hidden-order state. A previously observed 2-fold contribution of Si NMR linewidth is concluded to be due to extrinsic magnetic centers. Since the U and Si sites are aligned along the -axis, we conclude further that the electronic state shows 4-fold symmetry around the U site below the hidden-order transition. From this observed local symmetry, possible space groups for the hidden-order state are or , based on group theoretical considerations. Since the order vector is considered to be , the hidden-order state is then found to be with rank 5 odd-parity, i.e. electric dotriacontapolar order.
筒井 智嗣*; 金子 耕士; Pospisil, J.; 芳賀 芳範
Physica B; Condensed Matter, 536, p.24 - 27, 2018/05
Inelastic X-ray scattering (IXS) experiments of RTAl ( = La Ce, = Cu, Au) were carried out at 300 and 5.5 K. The spectra between LaCuAl and CeCuAl (LaAuAl and CeAuAl) are nearly identical at both temperatures except for temperature factors such as temperature dependence of Bose factor in IXS spectra and effect on thermal expansion. This means that no evident temperature dependence of IXS spectra was observed in CeTAl ( = Cu, Au).
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
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.
野間 雄一郎*; 小手川 恒*; 久保 徹郎*; 藤 秀樹*; 播磨 尚朝*; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*; 伊藤 公平*; Haller, E. E.*; et al.
Journal of the Physical Society of Japan, 87(3), p.033704_1 - 033704_5, 2018/03
Ge nuclear quadrupole resonance study of ferromagnetic superconductor UGe is reported. Detailed analyses successfully assigned crystallographic sites of Ge atoms. The measurement of the nuclear spin-lattice relaxation rate revealed highly anisotropic magnetic fluctuations.
芳賀 芳範; 山村 朝雄*
日本原子力学会誌, 60(3), P. 181, 2018/03
松本 裕司*; 芳賀 芳範; 立岩 尚之; 山本 悦嗣; Fisk, Z.*
Journal of the Physical Society of Japan, 87(2), p.024706_1 - 024706_4, 2018/02
Single crystal samples of UPtIn with the hexagonal structure are grown from indium flux. Strong uniaxial magnetic anisotropy is revealed from magnetic property measurements. Specific heat measurement reveals a significant deviation from -linear behavior, indicating the smaller electronic specific heat than the previous study.
立岩 尚之; Pospisil, J.*; 芳賀 芳範; 山本 悦嗣
Physical Review B, 97(6), p.064423_1 - 064423_10, 2018/02
強磁性体URhAlの磁気臨界現象を研究した。自発磁化の臨界指数、磁化率の指数、強磁性転移温度における磁化の臨界指数を求めた。それぞれ=0.2870.005, =1.470.02, =6.080.04と決定された。これらの臨界指数はWidomのスケーリング則()を満たしている。得られた結果は、二次元イジングモデルについての繰り込み群を用いた理論モデルで説明される。
黒田 健太*; 越智 正之*; 鈴木 博之*; 平山 元昭*; 中山 光大*; 野口 亮*; Bareille, C.*; 明比 俊太朗*; 國定 聡*; 室 隆桂之*; et al.
Physical Review Letters, 120(8), p.086402_1 - 086402_6, 2018/02
We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit coupling (SOC), we draw the topological phase diagram of CeX and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion.
服部 泰佑; 酒井 宏典; 徳永 陽; 神戸 振作; 松田 達磨*; 芳賀 芳範
Physical Review Letters, 120(2), p.027001_1 - 027001_5, 2018/01
In order to identify the spin contribution to superconducting pairing compatible with the so-called "hidden order", Si nuclear magnetic resonance measurements have been performed using a high-quality single crystal of URuSi. A clear reduction of the Si Knight shift in the superconducting state has been observed under magnetic field applied along the crystalline axis, corresponding to the magnetic easy axis. These results provide direct evidence for the formation of spin-singlet Cooper pairs. Consequently, results indicating a very tiny change of in-plane Knight shift reported previously demonstrate extreme uniaxial anisotropy for the spin susceptibility in the hidden order state.
Pospisil, J.; 芳賀 芳範; 中島 邦久; 石川 法人; Csaov, I.*; 立岩 尚之; 山本 悦嗣; 山村 朝雄*
Solid State Communications, 268, p.12 - 14, 2017/12
A new compound of the composition ScPdAl showing polymorphism has been discovered. At room temperature, it crystalizes in the orthorhombic structure, but it transforms into a cubic phase above 1053C. ScPdAl exists as a very stable intermetallic phase just in the vicinity of the icosahedral quasicrystal AlPdSc.
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; 松本 裕司*; 山本 悦嗣; 立岩 尚之; et al.
Physical Review B, 96(12), p.125117_1 - 125117_9, 2017/09
The Fermi surface and band structure of have been studied by angle resolved photoelectron spectroscopy (ARPES) with the incident photon energies of = 665-735 eV. Detailed band structure and the three-dimensional shape of the Fermi surface were derived experimentally, and they are quantitatively explained by the band-structure calculation based on the density functional approximation. Comparison of the experimental ARPES spectra of with those of shows that they have considerably different spectral profiles particularly in the energy range of - 1 eV. Some energy bands with their energy dispersions of about 1 eV observed in are missing in the ARPES spectra of measured along the same high symmetry line of Brillouin zone, suggesting that U 5 states form these bands in . The relationship between the ARPES spectra of and is very different from the case between and where their intrinsic difference is limited only in the very vicinity of the Fermi energy. The present result argues that the U 5 electrons in have strong hybridization with ligand states, and essentially have an itinerant character.
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
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.
Kim, H.*; 吉田 靖雄*; Lee, C.-C.*; Chang, T.-R.*; Jeng, H.-T.*; Lin, H.*; 芳賀 芳範; Fisk, Z.*; 長谷川 幸雄*
Science Advances (Internet), 3(9), p.eeao0362_1 - eeao0362_5, 2017/09
We report a first, real-space, imaging of an orbital ordered structure on a cobalt-terminated surface of the well-studied heavy fermion compound CeCoIn. Within small tip-sample distances, the cobalt atoms on a cleaved (001) surface take on dumbbell shapes alternatingly aligned in the  and  directions in scanning tunneling microscopy topographies. First-principles calculations reveal that this staggered orbital order is triggered by enhanced on-site Coulomb interaction at the surface.
芳賀 芳範; 松本 裕司*; Pospisil, J.; 立岩 尚之; 山本 悦嗣; 山村 朝雄*; Fisk, Z.*
Journal of Physics; Conference Series, 807(1), p.012015_1 - 012015_4, 2017/04
Transport characteristics of an antiferromagnetic uranium compound URhIn are studied. The antiferromagnetic transition leads to a formation of a gap on the Fermi surface as demonstrated by a hump in the resistivity behavior as a function of temperature. Hall effect, magnetoresistance and de Haas-van Alphen study consistently demonstrate a small carrier concentration in the antiferromagnetic state suggesting that majority of the Fermi surface vanishes.
Pospisil, J.; 郷地 順*; 芳賀 芳範; 本多 史憲*; 上床 美也*; 立岩 尚之; 神戸 振作; 長崎 尚子*; 本間 佳哉*; 山本 悦嗣
Journal of the Physical Society of Japan, 86(4), p.044709_1 - 044709_6, 2017/04
The effect of hydrostatic pressure on the electronic state of the antiferromagnet UIrGe is reported. A series of resistivity measurements up to 15 GPa demonstrated the Neel temperature decreases with increasing pressure and vanishes around 12 GPa. The transition from antiferromagnetic to paramagnetic phase appears to be of first order. A moderate increase in the effective mass was detected in the vicinity of the critical pressure.