Lead borate and lead silicate were added to lower the sintering temperature of a Ni0.5Zn0.5Fe2O4 ferrite prepared from the blend of two types of powders and to homogenize the grain size. 5PbO center dot SiO2 and 5PbO center dot B2O3 flux systems were added to lower the sintering temperature and diminish the magnetic loss at high frequencies. The ferrites were studied by bulk density, scanning electron microscopy and impedance analysis. It was found that the addition of PbO markedly accelerated the grain growth, while SiO2 and B2O3 were found to be effective to obstruct the movement of grain boundaries and to minimize the grain size. Doping with PbO in the mixed powders appropriately increased the densification and initial permeability. The ferrite doped with 1% of 5PbO center dot SiO2 possessed the lowest loss tangent (tg delta) in the range of 5 M-40 MHz and the highest threshold frequency. (c) 2006 Elsevier Ltd. All rights reserved.