Development of Elongated Particle Magnets

The development of permanent magnet materials is briefly reviewed. The present status of fine particle magnets is discussed from the viewpoint of our present understanding and lack of understanding of their behavior. The present methods of preparation and the various theoretical descriptions of the properties of elongated particles are reviewed. New work is presented relating the parameters of preparation to the resulting diameter of the elongated particles prepared by electrolysis into mercury. Rotational hysteresis,coercive force, and coercive force as a function of orientation are reported for particle diameters from 130 A to 305 A. Their behavior is compared to various theoretical descriptions and found to correspond to a noncoherent magnetization reversal mechanism most similar to the chain-of-spheres fanning model rather than the curling, buckling or coherent rotation models. Iron and iron-cobalt alloy particle magnets are described with maximum energy products up to 4.3 and 6.5 million gauss-oe, respectively.