Effects of microstructure on the permeability and loss of $Ni_{0.4}Zn_{0.6}Fe_2O_4$, $Ni_{0.4}Zn_{0.6}Fe_2O_4 + 0.01 V_2O_5$ and $Ni_{0.4}Zn_{0.6}Fe_2O_4 + 0.001 Bi_2O_3$ have been investigated.
Three kinds of specimens were calcined at 900 ℃ for 3 hours in air and then sintered at various temperatures for 5 hours in air.
$V_2O_5$-doped Ni-Zn ferrites showed the highest densification rate, followed $Bi_2O_3$-doped Ni-Zn ferrites and then Ni-Zn ferrites specimen.
Abnormal grain growth occured in $Bi_2O_3$-doped specimen. Average grain size increased with sintering temperature for $V_2O_5$-doped and Ni-Zn ferrites specimens.
$V_2O_5$-doped specimen showed markedly lower initial permeability than Ni-Zn ferrites specimen, and the linear relationship between initial permeability and grain size.
However, the initial permeability increased up to the grain size of 5.9 ㎛ and then decreased for Ni-Zn ferrites specimen.
The experimental results of the present Ni-Zn ferrites specimens showed that the domain wall relaxation frequency and maximum-loss frequency were shifted to higher frequencies with decreasing grain size.
