The microstructure and magnetic properties of $Ni_{0.4}Zn_{0.6}Fe_2O_4$ with the addition of $Bi_2O_3$ and $Nb_2O_5$ have been investigated. The effects of the additives on the sintering of $Ni_{0.4}Zn_{0.6}Fe_2O_4$ were also studied.
The amounts added were 0.0025, 0.005 and 0.01 mole fraction for $Bi_2O_3$ and 0.01 mole fraction for $Nb_2O_5$. All specimens were prepared by conventional method and sintered for 5 hours in air.
The densification rate of specimens with additives was found to be greater than that of pure specimens. The effect of $Bi_2O_3$ on the densification rate was greater than that of $Nb_2O_5$. Before the final density was obtained, abnormal grain growth occurred in the specimens with additives. But abnormal grain growth was not observed in pure specimens. The average grain size decreased with the increase of $Bi_2O_3$.
Up to the certain sintering temperature, the initial permeability increased, but above this temperature it began to decrease. As the sintering temperature increased, Q-value decreased. For the specimens with the same density, the initial permeability decreased with the increase of $Bi_2O_3$. The highest μxQ value was obtained in the specimen with the addition of 0.0025 mole fraction for $Bi_2O_3$ sintered at 975℃.
