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Pt
Al
太田 玖吾*; 松本 裕司*; 渡部 悠貴*; 金子 耕士; 田端 千紘; 芳賀 芳範
New Physics; Sae Mulli, 73(12), p.1170 - 1173, 2023/12
ハニカム格子を持つ反強磁性体UPtAlの磁気構造を決定するために中性子散乱実験を行った。UPtAlは
=9Kと
=26Kで二つの相転移を示す。 
の第一相では、
=(1/3, 0, 0)の伝搬ベクトルで記述される磁気反射が観測された。のフェーズIIでは、=(1/3, 0, 0)と
=(1/2, 0, 0)の磁気反射が観測され、=(1/3, 0, 0)の磁気反射強度は弱いが有限であった。温度依存強度のヒステリシスはでの相転移にまたがって観測され、での転移が1次転移であることを示唆している。
酒井 宏典; 常盤 欣文; Opletal, P.; 木俣 基*; 淡路 智*; 佐々木 孝彦*; 青木 大*; 神戸 振作; 徳永 陽; 芳賀 芳範
no journal, ,
最近、我々は溶融塩フラックス法により超伝導UTeの純良単結晶育成に成功した。これらの純良単結晶は、残留抵抗比が大きく、超伝導転移温度
以下の残留比熱も小さい。今回、純良単結晶を用いて、磁化困難軸である
軸方向に磁場をかけた時の超伝導相図を、電気抵抗率と交流帯磁率の同時測定により、正確に決定した。その結果、低磁場超伝導相と高磁場超伝導相が、全く異なる磁場角度依存性を示すことを明らかにした。また、高磁場超伝導相が現れる特徴磁場が、試料純良性によらず、約15Tと一定であること、低磁場超伝導相内にピン留め力の小さな中間超伝導相が新たに現れることなどを見出した。
Ge
; de Haas-van Alphen study芳賀 芳範; 山本 悦嗣; 仲村 愛*; 本多 史憲*; 青木 大*; 松本 裕司*; 山村 朝雄*; 白崎 謙次*; 山上 浩志*
no journal, ,
Electronic structure of the actinide compound ThRhGe is investigated using de Haas-van Alphen effect. The peculiar electronic structure possibly arising from the non-centrosymmetric hexagonal crystal structure is discussed.
Zn
北澤 崇文; 徳永 陽; 芳賀 芳範; Opletal, P.; 酒井 宏典; 常盤 欣文; 山本 悦嗣; 神戸 振作; 池田 陽一*; 藤田 全基*
no journal, ,
Possible multiorbital Kondo effect occurring in URhZn is examined by diluting with non-magnetic Lu. An experimental signature of a local maximum in magnetic susceptibility 
disappeared in the diluted Lu
U
RhZn, suggesting that the anomaly in can be attributed to intersite correlation effects rather than the single-site property.
Si金子 耕士; Stockert, O.*; 田端 千紘; 桑原 慶太郎*; 鬼柳 亮嗣; 中尾 朗子*; Krellner, C.*; Geibel, C.*
no journal, ,
Novel physical phenomena, such as superconductivity and non-Fermi liquid behavior, emerge in the vicinity of a quantum critical point (QCP). YbRhSi has been extensively studied owing to its proximity to an antiferromagnetic (AFM) QCP at ambient pressure. The AFM order at 
= 70 mK is suppressed by a weak external magnetic field. An inelastic neutron scattering study revealed a competition between ferromagnetic and incommensurate spin fluctuations at q' close to the zone center in YbRhSi, and evolution of resonance-like response at q=0 under magnetic fields. These features suggest an importance of ferromagnetic fluctuations in this system, where as a static AFM order was not confirmed at q'. This fact indicates that the AFM order in YbRhSi may have a different characteristic wave vector. As the latest study discovers emergence of superconductivity at very low temperature, recurring interests on nature of the AFM order burst. A search for an AFM Bragg reflection in YbRhSi has extreme difficulties arising from extremely low , and correspondingly a tiny ordered moment. To overcome these difficulties, we focus on isoelectronic substitution, where substitution of Rh with Co leads to a stabilization of the magnetic order. The huge enhancement of through the Co doping provides us with an opportunity to study the magnetic order closely. Our latest single crystal neutron scattering experiment was carried out on a lower Co concentration of 0.18. A new form of the AFM ordering vector was revealed in the ground state. This provides new insights into magnetic properties of YbRhSi.
under magnetic field along the easy a-axis常盤 欣文; Opletal, P.; 酒井 宏典; 山本 悦嗣; 神戸 振作; 徳永 陽; 芳賀 芳範; 木俣 基*; 淡路 智*; 佐々木 孝彦*; et al.
no journal, ,
磁化と磁気熱量効果の測定から得られたエントロピーを分析することにより、磁気容易a軸に沿った磁場下でのUTeの超伝導とメタ磁性の間の関係性を調べた。超伝導転移温度
以上の常伝導状態では、エントロピーが弱いメタ磁性による異常な増強を示す。驚くべきことに、異常は超伝導状態の中でも持続し、鋭い異常に変化する。異常は磁場の増加に伴うエントロピーの段階的な増加であり、吸熱に対応する。このように、メタ磁性が超伝導状態で一次相転移を引き起こすという前例のない現象を発見した。本研究では、この相転移が同じ
間の転移であり、相転移において
超伝導成分の重みが階段状に増加すると考えると、観察と一致することを議論する。
石飛 尊之; 服部 一匡*
no journal, ,
Some rare-earth-based compounds with the ZrNiAl-type structure exhibit intriguing physical phenomena due to the lack of inversion symmetry and magnetic frustration in the distorted Kagome lattice of the rare earth site. For example, HoAgGe is a potential candidate for kagome spin ices [1], and UCo
Ru
Al shows a colossal anomalous Nernst effect attributed to Weyl points [2]. In URhSn, unusual two-stage phase transitions at 
K and 
K have been observed [3]. While the low-temperature () ordered phase below is a typical ferromagnetic order present in the family compounds, the order parameter for the high- ordered phase in 
remains unknown. One feature of the high- order is that 
increases with increasing out-of-plane magnetic field [3]. This implies a non-magnetic order, as for the absence of the spectrum splitting at Sn sites in the M
ssbauer effect [4]. Here, we present an effective 
model, based on the observed magnetic entropy and Curie-Weiss temperature, and analyze it, using the mean-field approximation. We propose that the order parameter below is a 
structure of 
and 
type electric quadrupoles with chiral or polar symmetry. These orders can reproduce the observed magnetic-field dependence of . A chiral-polar switching phase transition may be realized under pressure, resolving the anomalous pressure-temperature phase diagram [5]. Below , a non-coplanar magnetic order with uniform magnetization perpendicular to the Kagome plane is realized, which may result in the anomalous Hall effect. The current scenario and whether the order parameter is chiral or polar can be examined through magnetoelectric effects and NMR measurements. Notably, the domain of chirality or polarity can be controlled by external magnetic fields. Thus, URhSn provides an ideal platform for investigating chiral and polar orders in metals.
Opletal, P.; 酒井 宏典; 芳賀 芳範; 三宅 厚志*; 徳永 将史*; 常盤 欣文; 山本 悦嗣; 神戸 振作; 徳永 陽
no journal, ,
UOX (X = S, Se, Te) crystallizes in tetragonal PbFCl-type structure (P4/nmm space group). Only polycrystalline samples are reported in literature. UOS, UOSe and UOTe were reported to be antiferromagnets with T
= 55, 100 and 160 K, respectively. Magnetic structure of UOS and UOSe were reported to have moment along the c-axis with Q = (0,0,1/2). UOS and UOSe were both reported to exhibit semiconducting behavior on polycrystalline samples. UOTe was theoretically predicted to have nontrivial topology. We have prepared first single crystals of UOX (X = S, Se, Te) and shown they exhibit semimetallic conductivity and UOS exhibits increase of T by almost 30 K in contrast to published literature. We will present the method of preparation of single crystals, results of magnetic, transport, thermal measurements, all effect and data obtained in high magnetic fields. We will discuss these results in connection to Weyl semimetals and results published in literature and anisotropy observed in electric resistivity.
田端 千紘; 今 布咲子*; 網塚 浩*; 清水 悠晴*; 青木 大*; 中尾 裕則*
no journal, ,
Magnetic materials with no inversion center at the magnetic site have attracted much attention from the viewpoints of chiral magnetic orders and electromagnetic effects in recent years. URhSn has a crystal structure without spatial inversion symmetry (hexagonal, space group P-62m) consisting of distorted Kagome layers, and according to previous reports on polycrystalline samples, it undergoes a two-step phase transition at To = 54 K and TC = 16 K. While the low-temperature phase is considered a ferromagnetic phase with spontaneous magnetization along the c-axis, the order parameter of the high-temperature phase has remained unknown for decades. No symmetry breaking has been detected for this mysterious phase by microscopic measurements such as powder neutron diffraction and Mossbauer spectroscopy. We recently succeeded in growing high-quality single crystals of this compound and clarified its detailed bulk properties (specific heat, magnetization, electrical resistivity, and thermal expansion). Interestingly, the high-temperature phase below To isstabilized by a magnetic field parallel to the c-axis, despite the absence of a c-axis spontaneous magnetization component. This peculiar behavior indicates neither a simple ferromagnetic nor antiferromagnetic scenario. We investigated the order parameter of this unknown phase using a resonant X-ray scattering (RXS) technique. On the resonance condition at the M4 absorption edge of U, we observed a slight increase in the intensity of a fundamental Bragg reflection below To, suggesting an order parameter with q = 0 that does not break the translational symmetry of the crystal. The observed RXS signal can be interpreted by either case of order parameters of magnetic dipoles and electric quadrupoles. Given the Sn-Mossbauer and Sn-NMR reports of no internal magnetic field associated with the order, an electric quadrupolar order is more plausible.
