Abstract:To improve the performance of Ni-Zn ferrites for power field use, the influence of MnO₂ additive on the properties of Ni-Zn ferrites was investigated by the conventional powder metallurgy. The results show that MnO₂ does not form a visible second phase in the doping mass fraction range of (0−2.0%). The average grain size, sintering density and real permeability gradually decrease with the increase of the MnO₂ content. And the DC resistivity continuously increases with the increase of MnO₂ content. The saturation magnetization (magnetic moment in unit mass) first increases slightly when mass fraction of MnO₂ is less than 0.4% MnO₂, and then gradually decreases with increasing the MnO₂ mass fraction due to the exchange interaction of the cations. When the excitation frequency is less than 1 MHz, the power loss (P_cv) continuously increases with increasing the MnO₂ content due to the decrease of average grain size. However, when the excitation frequency exceeds 1 MHz, eddy current loss gradually becomes the predominant contribution to P_cv. And the sample with a higher resistivity favors a lower P_cv, except for the sample with 2.0% MnO₂. The sample without additive has the best P_cv when worked at frequencies less than 1 MHz; and the sample with 1.6% MnO₂ additive has the best P_cv when worked at frequencies higher than 1 MHz.

Key words: Ni-Zn ferrite; MnO₂; doping; magnetic properties