Comparison between the Kittel and Polder resonances in polycrystalline ferrites

Kittel and Polder resonance parameters in polycrystalline ferrite spheres have been determined simultaneously using the perturbation theory. Measurements were made with the same sample in order to establish a proper comparison between the Kittel and Polder parameters. The meaning of the shift of the ferromagnetic resonance field and the different parameters used to characterize the resonance losses in polycrystalline ferrites are discussed. Discrepancies between the Kittel and Polder parameters are explained by studying the dependence of the linewidth and the ferromagnetic resonance field on the applied field. There is good agreement between the experimental results and the theoretical predictions