Ferromagnetic Resonance Loss in Lithium Ferrite as a Function of Temperature

Abstract

The ferromagnetic resonance linewidth as measured in ferrites is often dominated by loss due to ferrous ions. However, theoretical investigations of the scattering mechanisms in disordered magnetic materials such as ferrites have shown that volumetric disorder scattering should also play a significant role in determining the total linewidth of these materials. Lithium ferrite, Li0.5 Fe2.5O4, is one of the ferrites which in stoichiometric proportions would have all of the iron ions in the ferric state and which can have either an ordered or a disordered crystal structure at room temperature. It should thus be possible to reduce the contribution of ferrous ions so that the effects of disorder scattering can be observed by comparing the linewidths of ordered and disordered crystals. The data of this paper were taken on samples of lithium ferrite in which the linewidths are of the order of oersteds so that parallel pumping techniques can be used. The advantage of these measurements is that the role of surface scattering mechanisms is minimized and the resulting linewidth is the intrinsic linewidth for long-wavelength spin waves. Data are presented of intrinsic linewidth at microwave frequencies as a function of temperature from 290°K through a low-temperature maximum at 25°K. The value of the linewidth maximum in the disordered crystal proves to be quite anisotropic. Ordering the crystal increases the low-temperature maximum and alters the linewidth anisotropy. The effects of disorder scattering can be obtained from the linewidths above the low-temperature maximum and are shown to agree qualitatively with the predictions of theory.