Magnetotropic Response in Ruthenium Chloride

TL;DR

This paper analyzes the magnetic anisotropy in RuCl$_3$ using magnetotropic coefficient data to estimate exchange couplings, revealing that Kitaev interactions are not dominant in the material's effective Hamiltonian.

Contribution

It provides a quantitative estimation of exchange couplings in RuCl$_3$, showing that non-Kitaev interactions outweigh Kitaev couplings based on thermodynamic measurements.

Findings

Kitaev couplings are subdominant in RuCl$_3$

Exchange interactions are not purely Kitaev-like

Magnetotropic data constrains effective Hamiltonian parameters

Abstract

We consider the exchange couplings present in an effective Hamiltonian of $\alpha$-RuCl$_3$, known as the K-$\Gamma$ model. This material has a honeycomb lattice, and is expected to be a representative of the Kitaev materials (which can realize the 2d Kitaev model). However, the behaviour of RuCl$_3$ shows that the exchange interactions of the material are not purely Kitaev-like, especially because it has an antiferromagnetic ordering at low temperatures and under low strengths of an externally applied magnetic field. Fitting the data obtained from the measurements of the magnetotropic coefficient (the thermodynamic coefficient associated with magnetic anisotropy), reported in Nature Physics 17, 240-244 (2020), we estimate the values of the exchange couplings of the effective Hamiltonian. The fits indicate that the Kitaev couplings are subdominant to the other exchange couplings.