HYSTERETIC BEHAVIOR OF COBALT POWDERS

Spherical cobalt powders with mean diameters D between 0.5 and 8 μm and standard deviations σ, scaling approximately as 0.25D, have been prepared by a nonaqueous solution technique. Characterization of these powders has involved x-ray diffraction analysis, scanning electron microscopy, and differential thermal analysis. SEM reveals additional levels of substructure with size domains ranging from 0.2 to 0.3 μm and below. "As- prepared" powders revealed a microcrystalline structure through XRD analysis. High-temperature annealing (923 K) in flowing N2 resulted in a crystallographic change from microcrystalline to a preferred cubic crystal structure as evident through XRD. Room-temperature magnetization studies have been made by a vibrating sample magnetometer as a function of magnetic fields up to 20 kOe. Particular attention has been given to the coercivity and reduced remanence. The dependence of these quantities on the crystallinity of the powders will be briefly discussed.