An investigation on the dynamics of single (anti)skyrmion and multi-skyrmion structures in ferromagnetic nanodisks

We report a numerical study on the internal resonant modes of an antiskyrmion structure and  multi-skyrmion  in thin-film ferromagnetic nanodisks by using micromagnetic simulations. For the single antiskyrmion state,  we resolved several sets of resonant eigenmodes: gyrotropic mode and azimuthal and radial spin wave modes. At the in-plane field excitation,the gyrotropic mode behaves consistently with Thiele’s analytic theory, while a pair of twin azimuthal spin wave modes  demonstrate that their splitting is strongly relevant to the coexistent gyrotropic mode. At the out-of plane field excitation, several breathing like radial spin wave modes have been found. We also quantitatively investigate the dependence of the eigenfrequencies of these modes on the different parameter sets of the sample size and internal interactions.  For the multi-skyrmion,  we set  up a theoretic model with modified massless Thiele’s equations. Several theoretical expected gyrotropic eigenmodes were confirmed with their unique relative configurations among SK cores and by an IP magnetic field.