Non-collinear magnetic order in honeycomb Na₂PrO₃ revealed by single crystal torque measurements

The honeycomb antiferromagnet Na₂PrO₃ has recently attracted interest as a candidate to display unconventional magnetic behaviour from bond-dependent Kitaev interactions between 4f Pr⁴⁺ (j_eff = ¹/₂) moments [1], complementary to much explored Kitaev iridates and α-RuCl₃. We have succeeded in growing single crystals with no evidence for stacking faults or site mixing, and observe a sharp transition to long-range magnetic order at low temperatures, consistent with previously reported powder measurements [2]. Using highly-sensitive piezo-cantilever torque measurements on single-grain crystals we observe strongly contrasting angular dependence of the torque in orthogonal crystallographic planes, which can be naturally explained by a non-collinear, canted magnetic structure and we propose a minimal anisotropic exchange model to explain its stability, compatible with the crystal structure symmetry.

[1] S.-H. Jang, R. Sano, Y. Kato, and Y. Motome, “Antiferromagnetic Kitaev interaction in f-electron based honeycomb magnets,” Phys. Rev. B 99, 241106(R), 2019.

[2] M. J. Daum, A. Ramanathan, A. I. Kolesnikov, S. Calder, M. Mourigal, and H. S. La Pierre, “Collective excitations in the tetravalent lanthanide honeycomb antiferromagnet Na₂PrO₃,” Phys. Rev. B 103, L121109, 2021.