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

We have studied the thermal demagnetization in semi-infinite ferromagnets i n Fe/MnF2 and Fe/Mn bilayers using Mossbauer spectroscopy. We find that the hyperfine field at the Fe/MnF2 interface follows a quasilinear temperature dependence, which reverts to a T-3/2 dependence further into the bulk. The region in which linear temperature dependence was observed also showed sig nificantly higher spin canting than in the film's bulk layers. The interfac e in the Fe/Mn system immediately showed a T-3/2 dependence which persisted deeper into the bulk. We attribute the linear temperature behavior to surf ace spin wave modes created by a perpendicular surface anisotropy at the in terface. This behavior diminishes farther away from the interface, until th e hyperfine field goes like T-3/2 as expected for bulk, 3D spin waves. We c onclude that the perpendicular surface anisotropy is much stronger at the F e/MnF2 than the Fe/Mn interface. (C) 2000 American Institute of Physics. [S 0021-8979(00)01322-0].