Da. Dimitrov et Gm. Wysin, FREE VORTEX AND VORTEX-PAIR LIFETIMES IN CLASSICAL 2-DIMENSIONAL EASY-PLANE MAGNETS, Journal of physics. Condensed matter, 10(33), 1998, pp. 7453-7465
We report numerical simulation results for free-vortex lifetimes in th
e critical region of classical two-dimensional easy-plane ferro- and a
ntiferromagnets having three-component order parameters. The fluctuati
ons in the vortex number density in a spin dynamics simulation were us
ed to estimate the lifetimes. The observed lifetimes are of the same o
rder of magnitude but smaller than the characteristic timescale above
which a phenomenological ideal vortex-gas theory that has been used to
account for the central peak in the dynamic structure factor S-alpha
alpha(q,omega) is expected to be valid. For strong anisotropy, where t
he vortices are in-plane, the free vortex lifetimes for ferromagnets a
nd antiferromagnets are the same, while for weak anisotropy, where the
vortices have non-zero out-of-easy-plane components, the lifetimes in
antiferromagnets are smaller than in ferromagnets. The dependence of
the free-vortex and total vortex densities on the size dependent corre
lation length in the critical region is examined. We also determined t
he lifetimes of vortex-antivortex pairs for T = T-KT and well below T-
KT. The observed timescales are very short, and the observed pair dens
ities are extremely small. These results suggest that pair creation an
d annihilation are unlikely to play any role in the central peak in S-
xx(q,omega) observed in computer simulations for the ferromagnetic mod
el for T less than or equal to T-KT.