Impurity Ion Effects in the Ferrimagnetic Resonance of Ordered Lithium Ferrite

Experimental results are reported on the ferrimagnetic resonance linewidth, g factor, and magnetocrystalline anisotropy field of ionically ordered lithium ferrite monocrystals containing impurity ions. The measurements were made at frequencies ranging from 16.0 to 30.9 kMc and at temperatures ranging from 4.2° to 300°K. It is shown that: (a) the temperature dependence of the g factor is proportional to 1/T at ``high'' temperatures ${\text{(50}}^{\circ }\mathrm{K}{\text{≲T≤300}}^{\circ }\mathrm{K})$ but less pronounced at ``low'' temperatures ${\text{(T≲50}}^{\circ }\mathrm{K})$ ; (b) the linewidth vs temperature curves exhibit a maximum in the transition region (T ≈ 50°K) for all crystallographic directions which are not in the vicinity of [110]; (c) at 300°K the linewidth in the [111] direction increases linearly with increasing frequency; (d) all these experimental results can be interpreted on the basis of the theory of rapidly relaxing impurity ions proposed by Kittel and co‐workers. In regard to the anisotropy field, it is shown experimentally that at 4.2°K anomalous peaks exist in the [110] and [112] directions of the (110) plane, and that the amplitude of the former is twice that of the latter. An analysis based on Kittel's theory of anomalous anisotropy fields is supplemented by specific assumptions to explain both of these observations as well as the other details of the angular dependence of the anisotropy field.