Magnetization dynamics of soft nanocrystalline thin films with random magnetocrystalline anisotropy and induced uniaxial anisotropy

Results of frequency-dependent ferromagnetic resonance (FMR) measurements are presented for thin Fe-Zr-N nanocrystalline films with random magnetocrystal line anisotropy and induced uniaxial anisotropy. The study is done by changing the composition, the grain size and the magnitude of the induced anisotropy. We show that the magnetization dynamics is strongly influenced by the structural parameters of our samples. Although the frequency-dependent spectra can be analysed on the basis of the Landau-Lifshitz equation, an extra field H-shift has to be introduced in order to have agreement between the experiment and calculations. This extra field does not depend on the saturation magnetization and increases significantly when the grain size decreases from 10 to 2 nm. In addition, we observe a nonlinear decrease of the frequency linewidth with the applied dc field. After discussing various existing models we conclude that H-shift originates from variations in the magnitude of the magnetization, related with the nanocrystalline structure.