Skyrmion crystal and spiral phases in centrosymmetric bilayer magnets with staggered Dzyaloshinskii-Moriya interaction

TL;DR

This paper demonstrates how layer-dependent staggered Dzyaloshinskii-Moriya interactions in centrosymmetric bilayer magnets stabilize skyrmion crystal phases and other complex magnetic states, revealing new mechanisms for topological spin textures.

Contribution

It introduces a theoretical model showing that staggered Dzyaloshinskii-Moriya interactions combined with interlayer exchange stabilize skyrmion crystals in centrosymmetric bilayer magnets.

Findings

Skyrmion crystals form in bilayer triangular-lattice models under magnetic fields.

The skyrmion phases are robust against ferromagnetic and antiferromagnetic interlayer interactions.

Additional triple-Q states with opposite scalar chirality are identified in low- and high-field regions.

Abstract

We theoretically study a stabilization mechanism of the skyrmion crystal in centrosymmetric magnets with a bilayer structure. We show that the interplay between a layer-dependent staggered Dzyaloshinskii-Moriya interaction that arises from the absence of local inversion symmetry and the interlayer exchange interaction gives rise to a plethora of multiple-$Q$ states including the skyrmion crystal with a quantized topological number. By performing the simulated annealing for the bilayer triangular-lattice model under an external magnetic field, we demonstrate that the skyrmion forms the triangular-shaped crystals with different helicities in each layer owing to the staggered Dzyaloshinskii-Moriya interaction. Although the relative positions of the skyrmion core in each layer are different depending on the sign of the interlayer exchange interactions, the skyrmion crystal phases robustly appear under both ferromagnetic and antiferromagnetic interlayer interactions. We also find another two triple-$Q$ states with a uniform scalar chirality but without a quantized topological number in the low- and high-field regions. Especially, the low-field triple-$Q$ state exhibits the opposite sign of the scalar chirality to the skyrmion crystal, which are not found in the single-layer system. Our results indicate that the lack of local inversion symmetry in the lattice structure is another key ingredient to induce topological spin textures in centrosymmetric magnets.