Size and anisotropy determination by ferromagnetic resonance in dispersed magnetic nanoparticle systems

We present results for the FMR line shape modelling of non-interacting magnetic nanoparticle systems. We compare the results of the Smit and Beljers formalism and the usual linear-model, where the effective anisotropy field, HAeff, in the superparamagnetic regime is considered as a perturbation to the Zeeman interaction and added to the applied field, H. While the difference between these approaches is negligible for small HAeff (high temperature regime), it becomes more pronounced when HAeff∼H. We show how these results influence the determination of the parameters characterizing an array of random particles