Temperature and stress sensitivities of microwave ferrites

The effect of changes in remanent magnetization on the performance of microwave ferrites employed in latching phase shifter applications has been a serious problem for many years. Reductions in the remanence ratio R are caused both by increases in temperature and by stresses which arise from thermal or mechanical origins. Recently, the molecular field theory developed by Néel has been modified to account for the effects of possible sublattice canting on the magnetization-temperature curves of substituted microwave garnets. The results of this work have made it possible to compute magnetization-temperature characteristics for a wide range of substituted iron garnets. The problem of the stress sensitivity of R has also been examined theoretically, and it has been concluded that the ratio of the magnetostriction constant to the first-order anisotropy constant is the important variable. The magnetostriction constant involved depends on the relationship of the stress direction to the applied magnetic field. In comparison with experimental results for Y3MnxFe5-xO12in both single crystal and polycrystalline forms, the theory was shown to give at least qualitative agreement. This paper will serve as an up-to-date review of this work.