Skyrmion crystals in centrosymmetric triangular magnets under hexagonal and trigonal single-ion anisotropy

TL;DR

This paper theoretically demonstrates that specific types of single-ion anisotropy in centrosymmetric triangular magnets can induce skyrmion crystal phases, with stability depending on magnetic field direction and anisotropy type.

Contribution

It introduces a minimal spin model showing how hexagonal and trigonal single-ion anisotropy can stabilize skyrmion crystals in centrosymmetric triangular magnets.

Findings

Skyrmion crystals are stabilized by uniaxial or trigonal anisotropy under out-of-plane magnetic fields.

Hexagonal in-plane anisotropy stabilizes skyrmions under in-plane magnetic fields.

Various multiple-Q spin states depend on the type of single-ion anisotropy.

Abstract

We theoretically report an instability toward a skyrmion crystal in centrosymmetric magnets under hexagonal and trigonal single-ion anisotropy. The results are obtained for a minimal spin model with a crystal-dependent single-ion anisotropy on a triangular lattice by performing simulated annealing. By constructing magnetic phase diagrams in the presence of six different types of single-ion anisotropy while changing the amplitudes of external magnetic field and single-ion anisotropy in a systematic way, we find that the hexagonal and trigonal single-ion anisotropy becomes a source of the skyrmion crystal depending on the magnetic-field direction. We show that the skyrmion crystal is stabilized by the uniaxial-type or trigonal-type single-ion anisotropy under the out-of-plane magnetic field, while it is stabilized by the hexagonal-type inplane single-ion anisotropy under the inplane magnetic field. We also find various multiple-$Q$ spin states depending on the types of the single-ion anisotropy.