NORMAL-MODES OF VORTICES IN EASY-PLANE FERROMAGNETS

We investigate the linear spin-wave spectrum of two-dimensional easy-p lane classical Heisenberg ferromagnets in the presence of a vortex, us ing numerical diagonalization on small systems. The spectra of normal modes for both in-plane and out-of-plane vortices are determined, for square, triangular, and hexagonal lattices. Some of the modes show a s trong localization of their amplitudes near the center of the vortex. Moreover, we investigate a particular mode that drives the crossover i n the static vortex structure from purely in-plane to a vortex with we ll-localized out-of-plane component as the easy-plane character of the system is reduced below a certain threshold.