CrX3 (X = Cl, Br, I) have the same crystal structure and Hamiltonian but different ligand spin-orbit coupling (SOC) constant λX, providing excellent material platform exploring for exotic two-dimensional (2D) spin orders. Their microscopic mechanism underlying 2D spin physics remain unestablished, along with experimental corroboration of Kitaev exchange interaction, central to realizing topological quantum spin liquids. Finding direct evidence for Kitaev interaction and determining its value has been an essential but formidable challenge in Kitaev physics. Here we report the direct Kitaev interaction signature in magnetic anisotropy measured by ferromagnetic resonance (FMR) spectroscopy. We present measured values of Heisenberg J, Kitaev K, and off-diagonal symmetric Γ exchange interactions in CrX3 determined using FMR and exact diagonalization. K and Γ exhibit dominant dependencies on λX, indicating its central role in 2D magnetism. Our study provides a foundation for designing 2D magnetic materials exhibiting novel behaviors by tuning intrinsic material parameters such as SOC.
@article{arxiv.2405.16709,
title = {Spin-orbit coupling controlled two-dimensional magnetism in chromium trihalides},
author = {Inhee Lee and Jiefu Cen and Oleksandr Molchanov and Shi Feng and Warren L. Huey and Johan van Tol and Joshua E. Goldberger and Nandini Trivedi and Hae-Young Kee and P. Chris Hammel},
journal= {arXiv preprint arXiv:2405.16709},
year = {2026}
}