Investigation of the magnetoelastic coupling anisotropy in the Kitaev material $\alpha$-RuCl$_3$

TL;DR

This study combines theoretical and experimental approaches to analyze the anisotropic magnetoelastic coupling in $ ext{RuCl}_3$, revealing large magnetostriction anisotropy and directional magnetic effects influenced by magnetic torque, advancing understanding of its quantum spin-liquid properties.

Contribution

The paper provides a combined theoretical and experimental analysis of magnetoelastic anisotropy in $ ext{RuCl}_3$, highlighting the significant role of magnetoelastic coupling and torque effects in its magnetic behavior.

Findings

Magnetostriction anisotropy is unusually large compared to magnetization anisotropy.

Large, non-symmetric magnetic anisotropy observed for canted magnetic fields.

Magnetic torque effects significantly influence experimental measurements.

Abstract

The Kitaev material $\alpha$-RuCl$_3$ is among the most prominent candidates to host a quantum spin-liquid state endowed with fractionalized excitations. Recent experimental and theoretical investigations have separately revealed the importance of both the magnetoelastic coupling and the magnetic anisotropy, in dependence of the applied magnetic field direction. In this combined theoretical and experimental research, we investigate the anisotropic magnetic and magnetoelastic properties for magnetic fields applied along the main crystallographic axes as well as for fields canted out of the honeycomb plane. We found that the magnetostriction anisotropy is unusually large compared to the anisotropy of the magnetization, which is related to the strong magnetoelastic $\widetilde{\Gamma'}$-type coupling in our \textit{ab-initio} derived model. We observed large, non-symmetric magnetic anisotropy for magnetic fields canted out of the honeycomb $ab$-plane in opposite directions, namely towards the $+c^*$ or $-c^*$ axes, respectively. The observed directional anisotropy is explained by considering the relative orientation of the magnetic field with respect to the co-aligned RuCl$_6$ octahedra. Magnetostriction measurements in canted fields support this non-symmetric magnetic anisotropy, however these experiments are affected by magnetic torque effects. Comparison of theoretical predictions with experimental findings allow us to recognize the significant contribution of torque effects in experimental setups where $\alpha$-RuCl$_3$ is placed in canted magnetic fields.