Effects of additives on the loss characteristics of Mn–Zn ferrite

Abstract

In this study, the effects of the additives SiO2, CaO, TiO2, and Nb2O5 in various amounts on the high-frequency magnetic properties of Mn0.3Zn0.7Fe2O4 (MZFT) were investigated. The content of TiO2 and Nb2O5 was maintained at 2500ppm (0.25wt%) and 200ppm respectively, while that of SiO2 and CaO varied correspondingly from 0 to 100ppm and from 0 to 1000ppm. Results indicated that the sintering densities of the ferrites with additives appeared to be larger than that of the pure MZFT. No visible second phase was shown in the XRD patterns. The addition of SiO2 and CaO slightly increased the grain size of the ferrite, ranging from 6.89μm to 8.17μm, at 1275°C. The pure MZFT ferrite exhibited two maxima in the μi–T curves which were located at 220°C and 92°C and displayed a minimum power loss of 495mW/cm3 at ≈110°C in the PT–T curves. Addition of the additives was observed to shift the secondary maximum peak of the μi–T curves to ≈60°C. Among the samples, the compositions with 50ppm SiO2 and 1000ppm CaO additions, as well as with 100ppm SiO2 and 500 ppm CaO additions showed, respectively at 70°C and 60°C, the lowest total power losses of ≈290mW/cm3, which is 41.4% lower than that of the pure MZFT ferrite. This is due to the facts that the substitution of Ti4+ and Nb5+ in the spinel matrix triggered the formation of the strongly bound Ti4+–Fe2+ and Nb5+–Fe2+ pairs and thus reduced electron hopping in the ferrite lattices. On the other hand, SiO2 and CaO segregated to grain boundaries and formed electrically-insulating layers, thereby decreasing the contribution of the eddy current loss.