Thickness and temperature dependence of the dynamic magnetic behavior in disordered FePt films

We present in this work an investigation of the magnetic behavior of FePt films as a function of film thickness and thermal treatment. The films have been sputter-deposited on oxidized Si (1 0 0) crystals and are ferromagnetic at room temperature. Using ferromagnetic resonance techniques at 9.5 GHz we have studied a series of four films with a thickness in the range 10nm⩽t⩽100nm. The resonance spectra of these films were measured at and also above room temperature. The high temperature measurements produce irreversible changes in the samples which depend on the maximum temperature reached during the experiment. For relatively low measuring temperatures (T≲200∘C) the magnetic properties are generally improved, probably due to the release of stress formed during film fabrication. For larger temperatures (T>200∘C) the absorption linewidth gradually broadens and the line could be hardly observed at room temperature if the measuring temperature exceeded 300∘C. This behavior is due to the partial transformation of the metastable FCC phase to the ordered L10L10 high anisotropy phase. These data are consistent with the results found in samples annealed outside the resonant cavity.