Spin wave propagation near the surface of a ferromagnet with surface anisotropy

It is shown how the non-collinear spin ground state that generally results from an additional anisotropy energy at the surface of a ferromagnet alters the propagation of exchange dominated spin waves with wavevectors normal to the surface. These changes in propagation occur in a narrow region near the surface and for long wavelength spin waves are equivalent to changes in the spin wave boundary condition. These new boundary conditions show that the non-collinear ground state can substantially influence the spin wave resonance spectrum of thin ferromagnetic films.