Abstract
The effects of substitution of Mn2O3 for Fe2O3 Or CuO for MgO in MgZn ferrite have been studied in order to achieve low core loss, focusing on the microstructure, the initial permeability and the resistivity of MnZn, MnMgZn, and MnMgCuZn ferrites.
Initial permeability and resistivity of both MnMgZn and MnMgCuZn ferrites are higher than those of MgZn ferrite. Intragrain pores were observed in all of these ferrites. The pore density increases with grain growth.
The core loss of these ferrites consists of hysteresis loss and eddy current loss at frequencies lower than 120kHz. Hysteresis loss clearly depends on initial permeability because of magnetic anisotropy, grain size and pore density. It has been found that eddy current loss is related to the microstructure and not to the resistivity. It is suggested that the decrease in the amount of pores inside the grains is effective to lower hysteresis and eddy current losses.
Substitution of Cu enables MgZn ferrite to be sintered at lower temperatures, and it leads to the reduction of the core loss because of the formation of fine microstructure having small grain and low pore density. The lowest core loss (320kW/m3 at 100°C, 100mT and 100kHz) was achieved in the case of 11mol% CuO material sintered at 1120°C.
