Kinetic-anisotropy-induced ordering-orientation transitions calculated in CoPt alloys under various epitaxial growth conditions

We have investigated the epitaxial growth of CoPt alloy under various growth conditions. We find the equilibrium phase changes from the L1(0) [100] ordered structure to the L1(0) [001] ordered structure with the increase of the underlayer lattice constant parallel to the substrate plane. We show that there are two types of ordering-orientation transitions induced by kinetic anisotropy. When the lattice constant of underlayer is large, the ordered structure of CoPt films changes from the L1(0) [001] variant to the L1(0) [100] variant with the increase of growth rate. When the lattice constant of underlayer is small, the ordered structure of CoPt films changes from the L1(0) [100] variant to the L1(0) [001] variant, and then changes to L1(0) [100] variant with the increase of growth rate. These ordering-orientation transitions also occur with the decrease of temperature at adequate growth rate. We show that the underlayer with large lattice constant and the Pt buffer layer are suitable for the formation of the L1(0) [001] ordered structure.