LIFETIME OF VORTICES IN 2-DIMENSIONAL EASY-PLANE FERROMAGNETS

We use a combination of classical Monte Carlo and spin dynamics simula tions for the two-dimensional (2D) classical easy-plane ferromagnet to estimate the lifetime of free vortices near the Kosterlitz-Thouless t ransition temperature. The number fluctuations of free vortices are us ed to calculate the lifetime. The inverse lifetime gives an estimate f or a cutoff frequency below which an ideal-gas description of vortex d ynamics is inappropriate, We compare the lifetime results with simulat ions and ideal-gas phenomenology for the dynamic structure function, S -alpha alpha(q,omega). Motion of the vortices is observed only on a sh ort-range scale and the magnitude of the lifetime is mainly determined by processes of creation and annihilation of vortex-antivortex pairs rather than by vortex motion.