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arXiv · 2507.19853

Spin-flop-like transition as quantum critical point in Cs$_2$RuO$_4$

S. D. Nabi·M. Zhu·K. Yu. Povarov·D. G. Mazzone·J. Lass·Y. Wu·Z. Yan·S. Gvasaliya·A. Zheludev
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Abstract

We report thermodynamic, neutron diffraction, and inelastic neutron scattering measurements on Cs$_2$RuO$_4$, a member of the celebrated family of frustrated magnets Cs$_2$MX$_4$ (M = Cu, Co, X = Br, Cl). Unlike the previously studied members, it is based on $4d$ transition metal ions with $S=1$. Mapping out the $H-T$ magnetic phase diagram reveals an unusual continuous spin-flop-like phase transition associated with a quantum critical point within the antiferromagnetically ordered phase. A quantitative analysis of the complex magnetic excitation spectrum measured in zero field allows us to derive a model magnetic Hamiltonian for this compound. Its main feature is a frustration of magnetic anisotropy on a level that is much higher than in any of the previously studied species. This frustration naturally explains the peculiar phase transition observed.

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S. D. Nabi, M. Zhu, K. Yu. Povarov, D. G. Mazzone, J. Lass, Y. Wu, Z. Yan, S. Gvasaliya, A. Zheludev. 2025-10-21. Spin-flop-like transition as quantum critical point in Cs$_2$RuO$_4$. https://doi.org/10.1103/bds5-vkvm

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