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

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.

Skyrmion lattice in centrosymmetric magnets with local Dzyaloshinsky-Moriya interaction

“…Our phase diagram differs from that in Ref. [38], where more 3-Q states have been identified besides the skyrmion lattice phase.…”

“…Very recently, lattice spin Hamiltonian which reduces to Eq. ( 5) in the continuum limit by taking the ordering wave vector q → 0 was studied by Hayami [38]. Our phase diagram differs from that in Ref.…”

“…In Ref. [38], spins are defined on triangular lattice with q = π/3, while in the present work, we discretize the continuum model into a square lattice with a fine mesh to minimize the discretization effect.…”

“…In Ref. [38], Hayami restricted to the six in-plane wave vectors q i with |q i | = π/3 that are related by six-fold rotation in the simulations. This may also be a source of the discrepancy.…”