Ionic Ordering Effects in the Ferromagnetic Resonance of Lithium Ferrite Monocrystals

Ferromagnetic resonance experiments on ordered and disordered lithium ferrite monocrystals are reported. The resonance line width $\mathrm{\Delta H}$ , the g factor, and the magnetocrystalline anisotropy constants $K_1$ and $K_2$ were measured at temperatures ranging from 300°K to 4°K. Before an influence of ordering on $\mathrm{\Delta H}$ could be observed, it was necessary to reduce drastically several spurious effects. These included a large and strongly anisotropic $\mathrm{\Delta H}$ , which was attributed to a plastic deformation in a thin layer underlying the sample surface. After proper preparation of the samples, it was found that at all temperatures and crystallographic angles at which measurements were made, the value of $\mathrm{\Delta H}$ is either increased or relatively unchanged as a result of long-range cation ordering. It is concluded that in lithium ferrite, at least, spin wave scattering resulting from cation disorder is not the dominant source of linewidth: The observations include a large peak of $\mathrm{\Delta H}$ obtained in the [110] direction of the ordered samples at low temperatures, and a low value of $\mathrm{\Delta H}$ (3 oe) obtained in the [111] direction of the disordered samples at 4°K.