Improved parameters of manganese-zinc- and nickel-zinc-ferrites

The soft-magnetic Manganese-Zinc ferrites system has been known for more than 50 years. The continued study of the relationship between structure and properties, of ceramic processing optimisation possibilities as well as the improvement of the manufacturing machinery and equipment is due to the very good behaviour at high frequencies of these materials and their potential for possible further development. Possibilities of increasing the initial permeability of high-permeable Manganese-Zinc ferrites up to 20,000 during industrial processing as well as increasing of the usable transmission frequencies up to 3 MHz of high-performance Manganese-Zinc ferrites are presented in this paper. The optimisation of the parameters is based on a 8-10 components system whereby SiO2, CaO and TiO2 or alternatively SnO2, Nb2O5 and Ta2O5 are used as additives. Improved preparation technologies and new sintering techniques, especially a new generation of hood-type kilns, enable a oxygen partial pressure below 35 ppm O2 and ensure an efficient development of new components as well as material transport during the sintering process. Systems with 52 mole-% Fe2O3, 22 mole-% ZnO and 0.2 mass-% Bi2O3 provide initial permeabilities of 24,000 at room temperature and 45,000 at Hopkins point at a Curie temperature of 135°C. Nano-scaled ferrite microstructures prove to be materials with very special properties.