Magnetic properties of hot-pressed very fine-grained nickel ferrite

Hot-pressing of a Ni1/3Fe2/3coprecipitate at 300°C, 12 kbar resulted in the formation of a high density pellet of very fine-grained nickel ferrite, of which the crystallite size was 170 Å. The static magnetic properties were found to be very different from those of ordinary nickel ferrite. The magnetization under high magnetic field was much lower in value and was too hard to be readily saturated. In contrast, the Mössbauer spectra were not much different from those of ordinary ferrite. By annealing, the specimen first showed rather an unexpected enhancement in magnetic hardness and then gradually approached that of ordinary ferrite. A tentative model based on an assumption of strong interaction between the crystallites is discussed.