Structural Transition and Magnetic Anisotropy in $\alpha$-RuCl$_{3}$

TL;DR

This study investigates the structural phase transition and magnetic anisotropy in $ ext{α-RuCl}_3$, revealing how structural changes influence magnetic properties and potentially explain sample-dependent behaviors.

Contribution

It provides detailed insights into the structural transition from C2/m to rhombohedral R$ar{3}$ symmetry and its impact on magnetic anisotropy in $ ext{α-RuCl}_3$.

Findings

Structural transition involves stacking direction change from a-axis to b-axis.

Bond anisotropy disappears at the structural transition.

Magnetic anisotropy vanishes in the low-temperature rhombohedral phase.

Abstract

We report X-ray diffraction and magnetic susceptibility studies of the structural phase transition in $\alpha$-RuCl$_{3}$. By utilizing a single crystal sample with predominantly single twin domain, we show that $\alpha$-RuCl$_{3}$ goes from high-temperature C2/m structure to a rhombohedral structure with R$\bar{3}$ symmetry at low temperature. While the defining feature of the structural transition is changing the stacking direction from the monoclinic a-axis to the b-axis, bond-anisotropy disappears when the structural change occurs, indicating that the local $C_3$ symmetry is restored within the honeycomb layer. The symmetry change is corroborated by the vanishing magnetic anisotropy in the low-temperature structure. Our study demonstrates that magnetic interaction is extremely sensitive to structural details in $\alpha$-RuCl$_{3}$, which could explain the sample dependence found in this material.