Effects of Ta2O5 addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites

MnZn ferrites with the chemical formula Mn0.68Zn0.25Fe2.07O4 have been prepared by the conventional ceramic technique. Toroidal cores were sintered at 1350 °C for 4 h in N2/O2 atmosphere with 4% oxygen. Then the influence of Ta2O5 addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites was investigated by characterizing the fracture surface micrograph and measuring the magnetic properties over a temperature ranging from 25 to 120 °C. The results show that, when the Ta2O5 concentration is not more than 0.04wt%, the grain size has a slight increase with the increase of Ta2O5 concentration, the temperature of secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to lower temperature. However, excessive Ta2O5 concentration (>0.04wt%) results in the exaggerated grain growth and porosity increase, which make the initial permeability and saturation magnetic flux density decrease and the power loss increase at room temperature. Furthermore, the temperature of secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to about 100 °C.