Observation of two independent skyrmion phases in a chiral magnetic material

TL;DR

This study reports the discovery of a second, low-temperature skyrmion phase in Cu₂OSeO₃, stabilized by cubic anisotropy, expanding understanding of skyrmion phases beyond high-temperature conditions.

Contribution

The paper identifies a new low-temperature skyrmion phase in Cu₂OSeO₃ stabilized by cubic anisotropy, distinct from the known high-temperature phase, and provides theoretical modeling of its stabilization mechanism.

Findings

Discovery of a second skyrmion phase at low temperature.

The new phase exists only when magnetic field is along the <100> axis.

Theoretical evidence links stabilization to cubic anisotropy terms.

Abstract

Magnetic materials can host skyrmions, which are topologically non-trivial spin textures. In chiral magnets with cubic lattice symmetry, all previously-observed skyrmion phases require thermal fluctuations to become thermodynamically stable in bulk materials, and therefore exist only at relatively high temperature, close to the helimagnetic transition temperature. Other stabilization mechanisms require a lowering of the cubic crystal symmetry. Here, we report the identification of a second skyrmion phase in Cu$_{2}$OSeO$_{3}$ at low temperature and in the presence of an applied magnetic field. The new skyrmion phase is thermodynamically disconnected from the well-known, nearly-isotropic, high-temperature phase, and exists, in contrast, when the external magnetic field is oriented along the $\langle100\rangle$ crystal axis only. Theoretical modelling provides evidence that the stabilization mechanism is given by well-known cubic anisotropy terms, and accounts for an additional observation of metastable helices tilted away from the applied field. The identification of two distinct skyrmion phases in the same material and the generic character of the underlying mechanism suggest a new avenue for the discovery, design, and manipulation of topological spin textures.