Comparison of surface spin wave modes at Fe/MnF2 and Fe/Mn interfaces

We have studied the thermal demagnetization in semi-infinite ferromagnets in Fe/MnF2 and Fe/Mn bilayers using Mössbauer spectroscopy. We find that the hyperfine field at the Fe/MnF2 interface follows a quasilinear temperature dependence, which reverts to a T3/2 dependence further into the bulk. The region in which linear temperature dependence was observed also showed significantly higher spin canting than in the film's bulk layers. The interface in the Fe/Mn system immediately showed a T3/2 dependence which persisted deeper into the bulk. We attribute the linear temperature behavior to surface spin wave modes created by a perpendicular surface anisotropy at the interface. This behavior diminishes farther away from the interface, until the hyperfine field goes like T3/2 as expected for bulk, 3D spin waves. We conclude that the perpendicular surface anisotropy is much stronger at the Fe/MnF2 than the Fe/Mn interface