Skyrmion crystal with integer and fractional skyrmion numbers in a nonsymmorphic lattice structure with the screw axis

Abstract

The emergence of a magnetic skyrmion crystal in a nonsymmorphic lattice system with the screw symmetry is numerically investigated. By performing the simulated annealing for a layered spin model with the isotropic exchange interaction and the antisymmetric Dzyaloshinskii-Moriya interaction, and then constructing a lowtemperature phase diagram, we reveal that the skyrmion crystal is stabilized in both zero and nonzero fields even without the threefold rotational symmetry in the two-dimensional plane. We show that a competition between the ferromagnetic interlayer exchange interaction and the layer-and momentum-dependent anisotropic interactions is a source of the skyrmion crystals in the presence of the screw axis. Moreover, we find two types of layerdependent skyrmion crystals, which are characterized as a coexisting state of the skyrmion crystal and the spiral state, in the narrow field region. Our result provides a reference in the further search for skyrmion crystals in nonsymmorphic lattice systems.

Orthorhombic distortion and rectangular skyrmion crystal in a centrosymmetric tetragonal host

“…In these situations, the SkX is invariant under threefold or fourfold rotation. Meanwhile, it was revealed that SkXs remain stable in the low-symmetric lattice structures [42][43][44][45][46][47] and nonsymmorphic lattice structures with the screw axis [48]. In addition, a recent experiment has shown that a rhombic SkX was observed in the centrosymmetric tetragonal magnet EuAl 4 [49][50][51][52][53], where the importance of a spin-lattice coupling through a tetragonal-to-orthorhombic structural distortion was indicated in realizing such a low-symmetric SkX [54,55].…”