Neel Skyrmion interactions derived by their arrangement in regular lattices

The coarse-grained interactions between Néel skyrmions, stabilized by interfacial Dzyaloshinskii-Moriya coupling (iDMI), are studied through the properties of their hexagonal lattices by micromagnetic simulations. The interactions with the film edges are excluded by imposing periodic boundary conditions. The dependence of skyrmion size and interaction energy on the distance is derived. Two types of behavior are observed depending on the value of iDMI compared to the critical value Dc above which the skyrmion size diverges: For iDMI < Dc the skyrmions acquire a finite size that saturates at maximum value independent of the skyrmion distance that corresponds to the one of the isolated skyrmion. This energy is above that of the homogeneous ferromagnetic state. For iDMI > Dc the skyrmions tend to increase in size to the extent that their neighboring skyrmions permit and finite size skyrmions can be stabilized only in arrays due to their mutual repulsion. These configurations have energy below that of the homogeneous ferromagnetic state.