Cobalt-based anisotropic particles prepared by the polyol process

Cobalt and Co80Ni20 metal particles were prepared by reduction of acetate salts in a liquid polyol. The relative amount of the hcp phase and the probability of stacking faults in this phase vary with the experimental conditions of synthesis. The formation of either isotropic or anisotropic particles appears to be closely related to the stacking faults. Several kinds of anisotropic particles were detected by TEM: platelets, rods or diabolo-like particles. For isolated diabolos and rods, HRTEM and electron diffraction showed that the crystallographic c axis is parallel to the rotation axis of the particles. Magnetic property measurements showed high values of coercivity and remanence for the anisotropic particles. The anisotropic shapes differ markedly from those previously observed for cobalt-based particles prepared by the polyol process. A mechanism that involves a solid intermediate phase as either precursor or template is proposed.