Effect of pH on crystallographic orientation of plated cobalt films

Data is presented which contrasts the crystallographic and magnetic properties of films plated at low and at high pH. Plating from a simple CoSO4bath, an abrupt transition in preferred orientation is observed to occur in the region of pH 4, from orientation of the hexagonal c-axis predominantly parallel to the plane of the films below a pH of 4.0 changing to c-axis orientation predominantly perpendicular to the film plane in the pH range 4.0-6.5, together with corresponding changes in magnetic properties. A mechanism based on hydrolysis of Cobalt ions at the cathode interface is proposed to explain this behavior, which is supported by results from plating baths containing Boric acid.