Electrodeposited cobalt films: hcp versus fcc nanostructuring and magneticproperties

The crystallographic structure and morphology of electrodeposited cobalt fi lms on Au(111) is found to be very sensitive on the electrolyte pH value an d on the overpotential applied during deposition. The samples, 2 to 500 nm thick, where characterized by nuclear magnetic resonance (NMR), atomic forc e microscopy (AFM) and electron diffraction. The latter technique slows tha t the Co films grow in registry with the gold underlayer, reproducing the A u(111) texture. During the first stage of growth and depending on overpoten tial and pH value, either continuous hcp Co films or hcp Co islands are for med. Only the latter growth mode leads to an out of plane magnetization wit h 100% of remanence. Increasing the thickness, fee Co becomes the prevailin g phase. Eventually the fee to hcp ratio saturates at the same value regard less the overpotential. The thickness for which the equilibrium fee to hcp ratio is obtained as well as the sample structure and morphology before sat uration, depend strongly on the overpotential value. In any case, the predo minance of the fee Co phase leads to an in plane magnetization of the thick samples. This study opens up new opportunities of engineering the properti es of electrodeposited cobalt films.