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 obse rved in bulk equilibrium systems. These new materials are interesting for their magnetic properties, namely in some cases, their high magnet ocrystalline energy develops a perpendicular anisotropy, a property wh ich is required for magneto-optic recording. The occurrence of these n ew structures, that are metastable, is strongly dependent on the natur e and symmetry of the substrate, on the growth temperature and on depo sition rates. A general view of results obtained in Co-Pt and Co-Ru sy stems will be presented and the physical origin of these new structure s will be discussed.