Microstructure and magnetic properties of electrodeposited cobalt films

Cobalt films were electrodeposited onto both iron and copper substrates from an aqueous solution containing a mixture of cobalt sulfate, boric acid, sodium citrate, and vanadyl sulfate. The structural, intermetallic diffusion and magnetic properties of the electrodeposited films were studied. Cobalt electrodeposition was carried out in a passively divided cell aided by addition of vanadyl sulfate to keep the counter electrode clean. The divided electrolytic cell with very negative current densities cause the electrodeposited Co to adopt a face-centered cubic (fcc) structure, which is more magnetically reversible than the hexagonally close-packed (hcp) structured Co. The coercive field is also significantly less in the fcc-electrodeposited cobalt than in the hcp. SEM images show dense, uniform Co films without any cracks or porosity. Beside the deposition current, thickness of the film was also found to affect the crystal orientation particularly on iron substrates. Diffusion of cobalt film into the iron substrate was studied under reduced environment and a fast process was observed.