Features of ferromagnetic resonance in nanogranular films with perpendicular anisotropy of particles

Ferromagnetic resonance (FMR) in the blocked state of nanogranular magnetic films with perpendicular anisotropy of granules is considered for the magnetic field, which is perpendicular to the film plane, for the field strengths corresponding to the unsaturated magnetic state of the films. It is shown that in this case FMR response of the film is the sum of contributions from two subensembles of granules with the magnetic moments oriented “up” and “down” with respect to the film plane. These subensembles are coupled through the common demagnetization field of the film. It is established that FMR signals registered with the help of microwave detector direct current and a component of the detector current at the frequency of radiospectrometer magnetic field high frequency modulation are essentially different. It is shown that the distinction arises due to the fact that total magnetization of each of the subensembles and the film as a whole are practically not modulated by the high frequency modulation of the quasistatic magnetic field in the conditions of the ensemble blocked state and for the amplitude of modulation substantially smaller than the coercive field. Results of the phenomenon consideration within a simplified model are in a satisfactory qualitative agreement with the FMR measurement data for a Co0.54(Al2O3)0.46 film, basic characteristics of which satisfy requirements of the model.