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, H-A(eff), 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 H-A(eff) (high temperature regime), it becomes more pronounced when H-A(eff) approximate to H. We show how these results influence the determination of the parameters characterizing an array of random particles. (C) 2002 Elsevier Science B.V. All rights reserved.