Stability of N\'eel-type skyrmion lattice against oblique magnetic fields in GaV$_4$S$_8$ and GaV$_4$Se$_8$

TL;DR

This study investigates how Neel-type skyrmion lattices in GaV_4S_8 and GaV_4Se_8 are stable under oblique magnetic fields, mapping phase diagrams and comparing with theoretical predictions.

Contribution

It provides the first comprehensive experimental phase diagrams of skyrmion stability against oblique fields in these materials, revealing greater robustness than predicted.

Findings

Skyrmion phase withstands larger oblique angles than theory suggests.

Reentrant cycloidal phase observed in GaV_4Se_8.

Additional magnetic states linked to domain walls identified.

Abstract

The orientation of N\'eel-type skyrmions in the lacunar spinels GaV$_4$S$_8$ and GaV$_4$Se$_8$ is tied to the polar axes of their underlying crystal structure through the Dzyaloshinskii-Moriya interaction. In these crystals, the skyrmion lattice phase exists for externally applied magnetic fields parallel to these axes and withstands oblique magnetic fields up to some critical angle. Here, we map out the stability of the skyrmion lattice phase in both crystals as a function of field angle and magnitude using dynamic cantilever magnetometry. The measured phase diagrams reproduce the major features predicted by a recent theoretical model, including a reentrant cycloidal phase in GaV$_4$Se$_8$. Nonetheless, we observe a greater robustness of the skyrmion phase to oblique fields, suggesting possible refinements to the model. Besides identifying transitions between the cycloidal, skyrmion lattice, and ferromagnetic states in the bulk, we measure additional anomalies in GaV$_4$Se$_8$ and assign them to magnetic states confined to polar structural domain walls.