Electrodeposited cobalt films: hcp versus fcc nanostructuring and magnetic properties
Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS),
Université Louis Pasteur, 23 rue du Loess, 67037 Strasbourg Cedex, France
Revised: 3 July 2000
Published online: 15 October 2000
The crystallographic structure and morphology of electrodeposited cobalt films on Au(111) is found to be very sensitive on the electrolyte pH value and on the overpotential applied during deposition. The samples, 2 to 500 nm thick, where characterized by nuclear magnetic resonance (NMR), atomic force microscopy (AFM) and electron diffraction. The latter technique shows that the Co films grow in registry with the gold underlayer, reproducing the Au(111) texture. During the first stage of growth and depending on overpotential and pH value, either continuous hcp Co films or hcp Co islands are formed. Only the latter growth mode leads to an out of plane magnetization with 100% of remanence. Increasing the thickness, fcc Co becomes the prevailing phase. Eventually the fcc to hcp ratio saturates at the same value regardless the overpotential. The thickness for which the equilibrium fcc to hcp ratio is obtained as well as the sample structure and morphology before saturation, depend strongly on the overpotential value. In any case, the predominance of the fcc Co phase leads to an in plane magnetization of the thick samples. This study opens up new opportunities of engineering the properties of electrodeposited cobalt films.
PACS: 75.70.-i – Magnetic films and multilayers / 81.15.Pq – Electrodeposition, electroplating / 76.60.-k – Nuclear magnetic resonance and relaxation
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000