Preparation and magnetic properties of cobalt alloy particles

The preparation of submicroscopic chained cobalt and cobalt alloy particles by spontaneous autocatalytic reduction in protein solution has been studied. By varying the kind of protein, the average particle size can be easily varied from approximately 100 Å to 500 Å. The effects of the bath pH and hypophosphite content on the magnetic properties of the particles obtained are measured. It has been found that the coercive force can be increased at pH values from 8.0 to 8.5. However, coercive forces ranging from 300 Oe to 1000 Oe can be obtained by controlling the concentration of sodium hypophosphite. The rotational hysteresis integrals for the cobalt particles studied were in the range 1.2 to 1.8. These values are indicative of a single-domain chain of spheres model involving incoherent reversal.