SURFACE SPIN-WAVES IN HEISENBERG FERROMAGNETS WITH NONUNIAXIAL SINGLE-ION-ANISOTROPY

A Green-function formalism is employed to study the effect of nonuniaxial single-ion anisotropy on surface spin waves in semi-infinite Heisenberg ferromagnets with nearest-neighbor exchange interactions and at low temperatures T Tc. Results are deduced for the dispersion relations of surface spin waves in terms of the exchange and anisotropy parameters, which are assumed different at the surface compared with those of the bulk. The spin-correlation functions are also calculated as functions of the layer distances from the surface layer. © 1990 The American Physical Society.