Spin-orbit coupling controlled two-dimensional magnetism in chromium trihalides

TL;DR

This study investigates how spin-orbit coupling influences two-dimensional magnetism in chromium trihalides, providing experimental evidence of Kitaev interactions and quantifying exchange parameters crucial for designing novel 2D magnetic materials.

Contribution

It offers the first direct measurement of Kitaev interactions in CrX$_3$ using FMR spectroscopy and elucidates the role of SOC in 2D magnetic behavior.

Findings

Kitaev interaction signature detected via FMR

Quantified Heisenberg, Kitaev, and Gamma exchange parameters

Kitaev and Gamma interactions strongly depend on SOC constant

Abstract

CrX$_3$ (X = Cl, Br, I) have the same crystal structure and Hamiltonian but different ligand spin-orbit coupling (SOC) constant $\lambda_X$, 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 $\Gamma$ exchange interactions in CrX$_3$ determined using FMR and exact diagonalization. $K$ and $\Gamma$ exhibit dominant dependencies on $\lambda_X$, 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.