Mg–Mn–Al FERRITES FOR HIGH FREQUENCY APPLICATIONS

Abstract

The effect of substitution of nonmagnetic Al 3+ ions on the electrical and magnetic properties of Mg–Mn ferrites was studied in the ferrite series Mg 0.9 Mn 0.1 Al x Fe 2-x O 4 where x varied from 0–0.5 in steps of 0.1. The incorporation of Al 3+ ions in place of Fe 3+ ions results in a decrease of the lattice parameter owing to the smaller size of the substituted ions. The increase in dc resistivity has been observed at the expense of the deterioration of magnetic properties. A significant reduction in the values of the initial permeability, saturation magnetization and Curie temperature has been observed with successive increase of Al 3+ ions. These changes in properties have been explained on the basis of various models and other relevant factors, like modified cation distribution and magnetic interactions. The high dc resistivity, thereby lowering the dielectric losses, and the low value of the saturation magnetization are the desired characteristics of aluminium-substituted Mg–Mn ferrites used to prepare microwave devices operating in L, S and C bands.