Dynamics of vortices in quasi-two-dimensional classical Heisenberg magnets with weak easy-plane anisotropy

The authors present a discussion of the dynamical correlation functions for Heisenberg magnets with a weak easy-plane anisotropy for temperatures just above the Kosterlitz-Thouless phase transition. Compared to the XY-model they find here vortices which have in addition to the well known in-plane structure a localized out-of-plane profile around their centre. For the ferromagnetic case this structure produces an effective magnetic field which acts as a gyro force on the other vortices. Assuming a dilute gas of weakly interacting vortices, they find analytic expressions for the vortex contribution to the dynamical correlation functions. These results are compared (i) with numerical Monte Carlo-molecular dynamics simulations on a 100*100 square lattice allowing them to determine values for the vortex correlation length xi and average vortex velocity u and (ii) with experiments performed on different quasi-two-dimensional magnetic materials.