Analysis of low-temperature-fired NiCuZn ferrites for power applications

Abstract

NiCuZn ferrite materials fired at low temperature and containing 1.5 wt.% Bi 2O 3 and different Co 2O 3 concentrations have been prepared by the conventional ceramic technique. The samples were sintered for 4 h in air at 900 °C. The initial permeability decreased with the Co 2O 3 content due to local anisotropy induced by Co ions. The saturation magnetization increased with the Co 2O 3 content, which is attributed to the preference of Co ions for octahedral sites and their higher magnetic moment than those of Ni and Cu ions. Power loss under excitation at low magnetic flux density and low frequency first decreased, and then increased with increasing Co 2O 3 content due to the collective influence of the local induced anisotropy and the initial permeability. When the excitation frequency increased to 1 or 10 MHz, the power loss gradually decreased with increasing Co 2O 3 content, mainly because Co ions can decrease the concentration of Fe 2+ leading to a decrease in eddy current loss and residual loss for the ferrite samples. With increasing induction flux density, the effect of domain wall “freezing” caused by Co ions gradually disappears. For a flux density greater than or equal to the critical value of 50 mT, Co 2O 3 addition has a negative influence on decreasing the power loss of NiCuZn ferrites fired at low temperature.