Internal modes and magnon scattering on topological solitons in two-dimensional easy-axis ferromagnets - art. no. 024432

We study the magnon modes in the presence of a topological soliton in a two -dimensional Heisenberg easy-axis ferromagnet. The problem of magnon scatte ring on the soliton with arbitrary relation between the soliton radius R an d the ''magnetic length" Delta (0) is investigated for partial modes with d ifferent values of the azimuthal quantum numbers m. Truly local modes are s hown to be present for all values of m, when the soliton radius is large en ough. The eigenfrequencies of such internal modes are calculated analytical ly on the limiting case of a large soliton radius and numerically for arbit rary soliton radius. It is demonstrated that the model of an isotropic magn et, which admits an exact analytical investigation, is not adequate even fo r the limit of small radius solitons, R much less than Delta (0): there exi sts a local mode with nonzero frequency. We use the data of local modes to derive the effective equation of soliton motion; this: equation has the usu al Newtonian form in contrast to the case of the easy-plane ferromagnet. Th e effective mass of the soliton is found.