Ferromagnetic Resonance in Polycrystalline Nickel Ferrite Aluminate

Line broadening because of crystalline anisotropy and the random orientation of the crystallites is investigated for the case in which the anisotropy field is much larger than the saturation magnetization. The theory predicts an absorption line with shoulders on each side which correspond to grains in which a hard or an easy direction is aligned with the dc field. With increasing anisotropy the low-field side of the line becomes more prominent and for γHa/ω≳·5 a secondary absorption peak occurs on the low-field side of the main resonance. Measurements in nickel ferrite aluminates at X band agree reasonably well with the predictions, if it is assumed that the first order anisotropy constant is negative and that all higher order anisotropy constants are zero.