Ferromagnetic resonance in an ensemble of nanoparticles with randomly distributed anisotropy axes

Spectra of absorbed power as probed by ferromagnetic resonance (FMR) are numerically calculated within a macro-spin model for single domain nanoparticles using Landau–Lifshitz–Gilbert dynamics. Randomly distributed anisotropy axis and a distribution of anisotropy energies result in a significant broadening of the FMR signal as compared to an ensemble of particles all having the same anisotropy. Additionally, a temperature dependence of the shift of the resonance frequency is obtained which is in a qualitative agreement with experimental data on single domain nanoparticles.