Magnetic precursor to the structural phase transition in V$_2$O$_3$

TL;DR

This study uncovers a magnetic precursor to the structural phase transition in V2O3, showing that antiferromagnetic fluctuations and instabilities play a key role in driving the metal-insulator transition, especially under strain.

Contribution

It provides direct evidence of magnetic instability preceding the structural transition in V2O3, highlighting the interplay between magnetism and structural changes in the transition mechanism.

Findings

Magnetic instability occurs near the structural transition.

Antiferromagnetic fluctuations are present without a structural change.

Strain affects the congruence of magnetic and structural transitions.

Abstract

The coupling between structural, electronic and magnetic degrees of freedom across the metal-insulator transition in V2O3 makes it hard to determine the main driving mechanism behind the transition. Specifically, the role of magnetism has been debated and its interplay with the other transitions has not been established. To address this issue, we use a combination of muon spin relaxation/rotation, electrical transport and reciprocal space mapping which allows to correlate magnetic, electronic and structural degrees of freedom in strain-engineered V2O3 thin films. Evidence is found for a magnetic instability in the vicinity of the structural transition. This is manifested as a decrease in the antiferromagnetic moment with temperature leading to a virtual N\'eel transition temperature which coincides with that of the structural and electronic transitions. Moreover, we find evidence for an onset of antiferromagnetic (AF) fluctuations in the rhombohedral phase even without a structural transition to the monoclinic phase. The non-congruence of the structural and magnetic transitions increases as the transition temperature is reduced by strain. In samples where the transition is most strongly suppressed by strain, a depth-dependent magnetic state is observed. These results reveal the importance of an AF instability in the paramagnetic phase in triggering the metal-insulator transition and the crucial role of the structural transition in allowing for the formation of an ordered AF state.