Order by quenched disorder in the model triangular antiferromagnet RbFe(MoO4)2

TL;DR

This study demonstrates how quenched disorder from doping affects the magnetic ground state and magnetization plateau in the triangular antiferromagnet RbFe(MoO4)2, confirming the fluctuation-driven nature of its ground state.

Contribution

It provides experimental evidence that structural disorder lifts degeneracy in a frustrated magnet, revealing the fluctuation origin of its ground state and the impact of disorder on magnetic configurations.

Findings

Disappearance of the 1/3 magnetization plateau with doping

Disorder induces a transition to a less collinear magnetic state

Thermal effects can restore the pure compound's structure

Abstract

We observe a disappearance of the 1/3 magnetization plateau and a striking change of the magnetic configuration under a moderate doping of the model triangular antiferromagnet RbFe(MoO4)2. The reason is an effective lifting of degeneracy of mean-field ground states by a random potential of impurities, which compensates, in the low temperature limit, the fluctuation contribution to free energy. These results provide a direct experimental confirmation of the fluctuation origin of the ground state in a real frustrated system. The change of the ground state to a least collinear configuration reveals an effective positive biquadratic exchange provided by the structural disorder. On heating, doped samples regain the structure of a pure compound thus allowing for an investigation of the remarkable competition between thermal and structural disorder.