Zero-field skyrmion, meron, and vortex crystals in centrosymmetric hexagonal magnets

We investigate the interaction conditions to stabilize topological spin textures in centrosymmetric magnets without an external magnetic field. By performing the simulated annealing for an effective spin model with the momentum-resolved interaction on a two-dimensional triangular lattice, we find that the competing interactions between the finite -q channel and the uniform (q = 0) channel lead to a zero-field skyrmion crystal with the skyrmion number of +/- 1. Moreover, we obtain a variety of topological spin textures, such as a meron crystal, vortex crystal, and other multiple -Q states with and without a scalar chirality. We especially show that the bond-dependent anisotropic exchange interaction originating from the relativistic spin-orbit coupling plays an important role in inducing such topological spin textures, while the single-ion anisotropy does not.