S. Komineas and N. Papanicolaou
Department of Physics, University of Crete,
P.O. Box 2208, GR--710.03 Heraklion, Crete, Greece
and Research center of Crete.
Abstract
The dynamics of vortices in a 2D Heisenberg antiferromagnet with
an easy-plane anisotropy is studied numerically within the discrete spin
model as well as analytically within a continuum approximation based on a
suitable extension of the relativistic nonlinear sigma model. We find that
two like vortices scatter at 90o during a head-on collision,
whereas a vortex-antivortex pair is annihilated into spinwave radiation
emitted mainly at 90o . When a uniform bias field is applied,
vortex dynamics is affected rather profoundly and acquires the characteristic
features of the Hall effect of electrodynamics or the Magnus effect
of fluid dynamics. In particular, a single vortex is always spontaneously
pinned, two like vortices form a rotating bound state, and a
vortex-antivortex pair undergoes Kelvin motion. Finally, in the presence
of a bias field, vortices are shown to be the prominent topological
excitations even for an isotropic antiferromagnet.