A hot pressed coprecipitated ferrite and its application to magnetic heads

The nature of a coprecipitated ferrite powder has been studied and a hot pressed coprecipitated ferrite has been developed. A superior material, although hot pressed in air, was assumed due to a homogeneity of the powder, a partial oxidation of the powder and a low green density. A partial oxidation at 700°C in air decomposed the powder into a deformed spinel, α-Fe2O3and unknown phases and yet a microscopic homogeneity was not lost. This led to an easier control on sintering by reducing an excessive reactivity of the powder and introducing a reaction sintering. A low green density of less than 2 g/cm³resulted in a slow sintering and thus oxygen evolved at the initial sintering stage was not trapped in a sintered body and a reaction sintering permitted a high degree of densification. A continuous grain growth and an oxydizing atmosphere at an initial sintering stage contributed to segregate pores mainly at grain boundaries. A small grain size (about 50μm in average) and a reducing atmosphore of a SiC mold subsequently at high temperature were also effective and a hot pressing further reduced a porosity less than 0.05%. An appropriate reducing atmosphere also improved a permeability at 5MHz to 1000. Due to a high permeability and also due to an improved microstructure and thus a superior precission machinability, magnetic heads made of the new HPF exhibited twice as much output at 5MHz as the conventional one.