New metastable ordered structures in epitaxial Co-(Pt,Ru) alloy films

The preparation of Co-based alloy thin films by Molecular Beam Epitaxy (MBE) gives rise to a new class of materials that present long-range ordered structures or atomic stackings quite different from those observed in bulk equilibrium systems. These new materials are interesting for their magnetic properties, namely in some cases, their high magnetocrystalline energy develops a perpendicular anisotropy, a property which is required for magneto-optic recording. The occurrence of these new structures, that are metastable, is strongly dependent on the nature and symmetry of the substrate, on the growth temperature and on deposition rates. A general view of results obtained in Co-Pt and Co-Ru systems will be presented and the physical origin of these new structures will be discussed.