Magnetic and dielectric properties of low-loss MnZn ferrites with wide temperature stability

To meet the needs for higher energy efficiency and a wide operating temperature range of electric vehicles, the low-loss MnZn ferrites in a wide temperature range have been developed by optimizing the Fe content and the oxygen partial pressure (PO2) during the sintering process in this work. For the optimal sample, power loss at 300 kHz/100mT is 204 kW/m3 at 25 degrees C and remains below 290 kW/m3 in the wide temperature range from -10 to 120 degrees C. The loss separation method was employed to clarify the effects of the Fe content and PO2 on power loss. The equivalent circuit model has been employed to fit the complex impedance and it is found that the increase of PO2 enhances both the grain resistance Rg and the grain boundary resistance Rgb. The enhancement of Rgb is mainly responsible for the reduction of eddy current loss and consequently power loss. Dielectric permittivity is as large as about 15000 in this series of samples due to the electric polarization at the rich grain boundaries. Dielectric loss is very low between -50 and 150 degrees C and has little contribution to the energy loss.