Crystal structure of a magnetic cobalt layer deposited on a (111) gold surface determined by transmission electron microscopy

The behaviour of thin films of ferromagnetic metals has received a lot of attention recently owing to their new magnetic properties induced by the quasi-bidimensionality of the lattice. We have performed some studies on thin cobalt layers protected from oxidation by two gold films orientated with their surfaces roughly parallel to (111) planes. Cobalt can be either cubic or hexagonal in crystal structure and it is important to know the crystal structure in order to understand the magnetic properties of the layers. We have proved that the cobalt layer has a hexagonal structure; this can be related to the existence of an easy magnetization axis perpendicular to the film, and of a large magnetic anisotropy constant.