Ginzburg-Landau theory for skyrmions in inversion-symmetric magnets with competing interactions

TL;DR

This paper develops a Ginzburg-Landau theoretical framework for understanding skyrmions in inversion-symmetric magnets with competing interactions, revealing unique static and dynamic properties, including a new internal degree of freedom, and offering insights for future skyrmion research.

Contribution

It introduces a general Ginzburg-Landau theory for skyrmions in inversion-symmetric magnets, highlighting their unique internal degrees of freedom and coupling effects, expanding the understanding beyond non-centrosymmetric systems.

Findings

Skyrmions can be stabilized by easy axis spin anisotropy in inversion-symmetric magnets.

Skyrmions possess a new internal degree of freedom related to helicity rotation.

Coupling between orbital and spin degrees leads to novel skyrmion behaviors.

Abstract

Magnetic skyrmions have attracted considerable attention recently for their huge potential in spintronic applications. Generally skyrmions are big compared to the atomic lattice constant, which allows for the Ginzburg-Landau type description in the continuum limit. Such a description successfully captures the main experimental observations on skyrmions in B20 compound without inversion symmetry. Skyrmions can also exist in inversion-symmetric magnets with competing interactions. Here we derive a general Ginzburg-Landau theory for skyrmions in these magnets valid in the long wavelength limit. We study the unusual static and dynamical properties of skyrmions based on the derived Ginzburg-Landau theory. We show that an easy axis spin anisotropy is sufficient to stabilize a skyrmion lattice. Interestingly, the skyrmion in inversion-symmetric magnets has a new internal degree of freedom associated with the rotation of helicity, i.e. the "spin" of the skyrmion as a particle, in addition to the usual translational motion of skyrmions (orbital motion). The orbital and spin degree of freedoms of an individual skyrmion can couple to each other, and give rise to unusual behavior that is absent for the skyrmions stabilized by the Dzyaloshinskii-Moriya interaction. The derived Ginzburg-Landau theory provides a convenient and general framework to discuss skyrmion physics and will facilitate the search for skyrmions in inversion-symmetric magnets.