Abstract
It is not difficult to prepare the manganese-zinc ferrite having a high permeability. But such a ferrite is also accompanied with a considerable loss at high frequencies because of the high conductivity. For improving the practical characteristics, i.e. reducing the loss and increasing the initial permeability various impurities were added to the manganese-zinc ferrite Mn0.68Zn0.21Fe2.11O4+δ. The simultaneous addition of CaO and SiO2 to the ferrite was found to be effective for this purpose. The impurities change the electrical and magnetic properties as well as the sintering grain structure. The relation of these properties to the grain structure was studied. It was found that the small loss of the ferrites containing proper amounts of CaO and SiO2 was due to the grain structure consisting of fine grains separated from one another by high resistive layer. The excess of SiO2 provokes the discontinuous grain-growth forming so called duplex structure, which is unfavourable in reducing the loss at high frequencies. The excess of CaO reduces the permeability remarkably. Based on the experimental results obtained in this study an excellent ferrite with a very small quality-factor, tan δ⁄μ0<2×10−6 at 100 Kc, was prepared.
