Unusual increase in permeability in cobalt substituted Ni-Zn-Mg ferrites

A constant rise in magnetic permeability with a simultaneous decrease in saturation magnetization, and Curie temperature has been recorded throughout the cobalt concentration studied in Ni-Zn ferrite system of composition, Ni0.57−yCoyZn0.35Mg0.08Fe2O4 (x = 0.00, 0.04, 0.08, 0.12, 0.16, 0.20). The observed increase in magnetic permeability with cobalt addition has been an unusual phenomenon in nickel zinc ferrites. The anomalous increase along with allied magnetic properties has been discussed in terms of the super exchange interactions between the cations occupying tetrahedral and octahedral sites and their distribution by studying lattice parameter, grain size and differential magnetic susceptibility.