Magnetic phase diagram of the frustrated antiferromagnet Cs₂RuO₄

The celebrated family of distorted triangular lattice systems Cs₂MX₄ (M = Cu, Co, X = Br, Cl) gained much attention in the field of quantum magnetism, with recent advancements in Cs₂CoBr₄ [1-3]. We report single crystal bulk properties and preliminary neutron measurements of a new member, Cs₂RuO₄. Unlike the Cu and Co-based counterparts, its magnetism stems from a S = 1 4d transition metal ion Ru⁶⁺. It has stronger spin-orbit coupling and potentially features bond-dependent anisotropies in the spirit of the Kitaev model. We present thermodynamic measurements of susceptibility, specific heat, and high-field magnetization to map out an interesting H-T phase diagram and investigate the role of anisotropy. We observed magnetic order at T_N = 5 K and a spin-flop-like transition accompanied by a gap closing and reopening, reminiscent of a quantum critical point. Our findings further extend the explored parameter space of this intriguing family of materials.

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[2] L. Facheris, S. D. Nabi, A. Glezer Moshe, U. Nagel, T. Rõõm, K. Yu. Povarov, J. R. Stewart, Z. Yan, A. Zheludev, Phys. Rev. Lett. 130, 256702 (2023).

[3] L. Facheris, S. D. Nabi, K. Yu. Povarov, Z. Yan, A. Glezer Moshe, U. Nagel, T. Rõõm, A. Podlesnyak, E. Ressouche, K. Beauvois, J. R. Stewart, P. Manuel, D. Khalyavin, F. Orlandi and A. Zheludev, Phys. Rev. B 109, 104433 (2024).