Electrodeposited Cobalt Films: Alteration Caused by the Electrolyte pH

Cobalt (Co) films were electrodeposited on polycrystalline copper substrates at different pH values. It is observed that the crystal structure of the films converts from hexagonal close-packed (hcp) to a mixed phase of face centered cubic and hcp as the electrolyte pH decreases. The grain size calculated from the X-ray diffraction patterns decreases with the decrease of electrolyte pH. The surface of the films grown at a high pH is more uniform than that of the films grown at a low pH. The saturation magnetization and the coercivity decrease as the electrolyte pH decreases. The high coercivity value at high pH corresponds to the hcp crystal structure of the films as well as the large grain size of Co clusters. Magnetic measurements also reveal that the easy axis direction of magnetization is parallel to the film plane for all films since the higher remanent magnetization and lower saturation field are observed in parallel hysteresis loops.