Anisotropy of the zigzag order in the Kitaev honeycomb magnet $\alpha$-RuBr$_3$

TL;DR

This study investigates the magnetic anisotropy and zigzag magnetic order in the Kitaev candidate $ ext{α}$-RuBr$_3$ using torque magnetometry, revealing anisotropic interactions and domain behavior relevant to understanding its magnetic ground state.

Contribution

The paper provides detailed torque magnetometry measurements on $ ext{α}$-RuBr$_3$, identifying anisotropic interactions and domain effects that advance understanding of its magnetic anisotropy and zigzag order.

Findings

Easy-plane magnetic anisotropy with temperature-dependent torque amplitude.

Six-fold periodicity in torque reflecting crystal symmetry and domain stabilization.

Comparison with theory elucidates anisotropic interactions and domain competition.

Abstract

Kitaev materials often order magnetically at low temperatures due to the presence of non-Kitaev interactions. Torque magnetometry is a very sensitive technique for probing the magnetic anisotropy, which is critical in understanding the magnetic ground state. In this work, we report detailed single-crystal torque measurements in the proposed Kitaev candidate honeycomb magnet $\alpha$-RuBr$_3$, which displays zigzag order below 34 K. Based on angular-dependent torque studies in magnetic fields up to 16 T rotated in the plane normal to the honeycomb layers, we find an easy-plane anisotropy with a temperature dependence of the torque amplitude following closely the behaviour of the powder magnetic susceptibility. The torque for field rotated in the honeycomb plane has a clear six-fold periodicity with a saw-tooth shape, reflecting the three-fold symmetry of the crystal structure and stabilization of different zigzag domains depending on the field orientation, with a torque amplitude that follows an order parameter form inside the zigzag phase. By comparing experimental data with theoretical calculations we identify the relevant anisotropic interactions and the role of the competition between different zigzag domains in this candidate Kitaev material.