PHYSICAL REVIEW B 102, 134411 (2020) Strong magnetic anisotropy and unusual magnetic field reinforced phase in URhSn with a quasi-kagome structure Yusei Shimizu , 1 , * Atsushi Miyake, 2 Arvind Maurya, 1 Fuminori Honda, 1 Ai Nakamura, 1 Yoshiki J. Sato, 1 Dexin Li, 1 Yoshiya Homma, 1 Makoto Yokoyama , 3 Yo Tokunaga, 4 Masashi Tokunaga, 2 and Dai Aoki 1 1 Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan 2 Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan 3 Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan 4 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan (Received 5 June 2020; revised 31 August 2020; accepted 31 August 2020; published 9 October 2020) The physical properties of URhSn with quasi-kagome structure are studied using single-crystalline samples via electrical resistivity, magnetic susceptibility, heat capacity, thermal expansion, and high-field magnetization measurements. Remarkable magnetic anisotropy is found in the ferromagnetic (FM) state below T C = 16 K as well as in the ordered state between T C and T O = 54 K, where the easy and hard magnetization directions are the hexagonal [0001] and [10 ¯ 10] axes. In the paramagnetic state, the magnetic susceptibility shows a Curie- Weiss behavior; the Weiss temperatures are positive and negative for [0001] and [10 ¯ 10], respectively, indicating the presence of both FM and antiferromagnetic (AFM) correlations. The entropy release for 5 f electrons is approximately R ln3 at T O . The thermal expansion coefficient is strongly anisotropic around T O between the hexagonal basal plane and the [0001] axis, indicating its remarkable anisotropic magnetoelastic response and uniaxial stress dependences. Interestingly, the magnetic field response of the higher-temperature ordered state is unusual: T O (H ) increases and the heat-capacity jump is enhanced with the magnetic field for H || [0001]. Based on the established thermodynamic evidence for the second-order transition at T O (H ), a plausible scenario is the occurrence of a canted AFM ordering or a conical state under magnetic fields, which is stabilized when coupled with field-induced magnetic moments along the [0001] axis. Another possibility is the occurrence of quadrupole ordering at T O (H ). DOI: 10.1103/PhysRevB.102.134411 I. INTRODUCTION In solid-state physics, uranium compounds have attracted considerable interest because of their unusual properties, such as unconventional superconductivity [1–3], non-Fermi-liquid behavior due to quantum phase transitions [4], exotic Kondo effects [5], and metamagnetic instabilities [6–12]. Further- more, uranium systems show exotic orders, e.g., multipole orders in UCu 2 Sn [13–15], UNiSn [16], and UPd 3 [17,18], and the hidden order in URu 2 Si 2 [3], whose order parameter has not been understood for more than three decades [19]. Meanwhile, geometrically frustrated magnetic materials are fascinating for the investigation of novel quantum states, such as spin liquids [20,21], the spin nematic state [22], and chiral magnetism [23]. Hence, a study of frustrated magnetic sys- tems in uranium compounds with strong spin-orbit coupling would lead to a nontrivial research field. The uranium-based UTX (T = transition metals, X = Al and Sn) system, which crystallizes in the hexagonal ZrNiAl-type structure (space group: P ¯ 62m) without inversion symmetry in the crystal structure, is a good candidate for frustrated 5 f -electron systems. In particular, the ZrNiAl-type structure has a distorted kagome structure, which is comprised of a network of uranium triangular lattices [Figs. 1(a) and * yuseishimizu@imr.tohoku.ac.jp 1(b)]. Rare-earth-based ZrNiAl-type systems, such as CePdAl [24–29] and YbAgGe [30–32], show novel magnetic phase diagrams due to geometrical and magnetic frustration effects. Meanwhile, UTX compounds have provided various interest- ing properties due to the hybridization effects between 5 f and conduction electrons [33]; furthermore, they have been inves- tigated with a focus on their magnetic instability and quantum criticality [4]. For instance, UCoAl is a paramagnetic (PM) system at ambient pressure that exhibits an itinerant meta- magnetic (first-order) transition at 8 kOe with an Ising-type moment (0.3 μ B /U) [33,34]. It is considered that UCoAl is located in the vicinity of a tricritical point (TCP), as estimated at a negative pressure of −0.2 GPa [35]. Furthermore, the metamagnetic transition has been studied in detail based on tuning temperature (T ), pressure (P), and magnetic field (H ), demonstrating the wing structure in the T -P-H phase diagram [36–38]. Moreover, an isostructural ferromagnet URhAl ex- hibits a weak first-order ferromagnetic (FM) quantum phase transition at a critical pressure P c ∼ 5 GPa and non-Fermi- liquid behavior above P c [39]. In the present study, we focus on URhSn, which shows successive phase transitions at T C = 16 K and T O = 54 K [40–43]. Previous studies have reported only the results of polycrystalline samples [40–43], where the transition at T C was due to FM transition, whereas the nature of the or- dered phase below T O , which we call the higher-T ordered 2469-9950/2020/102(13)/134411(11) 134411-1 ©2020 American Physical Society