Modern developmental trends in the production and application of hard and soft magnetic ferrite materials

摘要

This paper discusses the state-of-the-art in developments of new ceramic ferrite materials. Even today, hard and soft ferrites play a dominant role in magnetic materials, and are produced in significant quantities. Although both material classesare used in a variety of applications, the parameters for using the currently available material qualities do not correspond to those desired by system designers. As a result, research and development in both industry and institutes have undertaken greatefforts to develop new classes of ferrite materials. Within the range of hard ceramic hexaferrite magnets, these efforts are directed towards optimising the magnetic parameters of these materials (remanence induction, coercive field strength, maximalenergy product). Examinations using the development of a material with a greater remanence induction (BR > 0,43 T) are shown as examples. The optimisation of the production technology for hard ferrites plays an important role, where the fine milling ofthe calcined raw material mixture is shown to be especially critical. Another possibility exists in influencing the bonds by appropriately doping the magnetic structure. In the area of soft ferrite materials, the development of optimised Mn-Zn ferrites is discussed which, because of their higher operating frequency (f=1 MHz) show only slight losses. After a short introduction into the properties of MnZn ferrites and the loss determining contributions, such complex topics as the purity of the raw materials, influence of the dopant, and the sintering process are presented with respect to their effects on the soft ferrite properties.