MAGNON MODES AND MAGNON-VORTEX SCATTERING IN 2-DIMENSIONAL EASY-PLANEFERROMAGNETS

We calculate the magnon modes in the presence of a vortex on a circula r system, combining analytical calculations in the continuum limit wit h a numerical diagonalization of the discrete system. The magnon modes are expressed by the S matrix for magnon-vortex scattering, as a func tion of the parameters and the size of the system and for different bo undary conditions. Certain quasilocal translational modes are identifi ed with the Frequencies which appear in the trajectory (X) over right arrow(t) of the vortex center in recent molecular dynamics simulations of the full many-spin model. Using these quasilocal modes we calculat e the two parameters of a third-order equation of motion for (X) over right arrow(t). This equation was recently derived by a collective var iable theory and describes very well the trajectories observed in the simulations. Both parameters, the vortex mass and the factor in front of (X) over right arrow, depend strongly on the boundary conditions.