We report comprehensive thermodynamic and neutron scattering measurements on the S = 3/2 antiferromagnet Cs2CoI4, a member of the thoroughly studied family of frustrated magnets Cs2MX4 (M = Cu, Co, Ru, X = Br, Cl, I, O). Unlike previously studied members, Cs2CoI4 undergoes a structural phase transition, for which we determine the low-temperature crystallographic structure. The resulting symmetry reduction strongly affects both the magnetic exchange interactions and single-ion anisotropy. Despite the large parameter space, we propose a minimal magnetic Hamiltonian that reasonably captures the observed excitation spectrum, analyzed using extended SU(4) linear spin-wave theory.
@article{arxiv.2603.08237,
title = {Magnetic phase diagram and spin Hamiltonian of antiferromagnet Cs$_2$CoI$_4$},
author = {S. D. Nabi and L. Facheris and V. Romerio and V. Kocsis and K. Yu. Povarov and D. Sheptyakov and J. Lass and D. G. Mazzone and H. Kikuchi and T. Masuda and S. A. Barnett and D. R. Allan and Z. Yan and S. Gvasaliya and A. Zheludev},
journal= {arXiv preprint arXiv:2603.08237},
year = {2026}
}