Chiral and polar quadrupole orders in URhSn

URhSnにおけるカイラル・ポーラー四極子秩序

石飛 尊之; 服部 一匡*

Ishitobi, Takayuki; Hattori, Kazumasa*

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 UCoRuAl 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 Mssbauer 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.