Preparation and properties of hot-pressed Ni-Zn ferrites for magnetic head application

Hot-pressed polycrystalline Ni-Zn ferrites have been prepared by two different technologies: the wet method and the ball-milling method. In the wet method, the ferrite was prepared from aqueous solutions of iron, zinc, and nickel hydrated sulphates which were dehydrated in a spray-drier at 250°C and decomposed at 800°C in air. In the ball-milling method, oxides of these same elements were used. It was observed that the wet method is better than the ball-milling technique for preparation of hot-pressed ferrites: coercive force Hcis lower, grain size is more homogeneous, initial permeability μ´0is increased, and it is easier to control grain growth after hot-pressing without recrystallization phenomenon. Furthermore, stoichiometry is a very important parameter to obtain the better compromise between initial permeability, electric resistivity, coercive force, and homogeneous grain size.