LATTICE-RELAXATION AND 3-DIMENSIONAL REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION ANALYSIS OF STRAINED EPITAXIAL CO/MN SUPERLATTICES

In situ observations of reflection high-energy electron diffraction (RHEED) are used to study the structure and growth of epitaxial Co/Mn superlattices on hcp (0001) Ru buffer layers. Mn deposited on fcc (111) or hcp (0001) Co presents a singular growth behavior which can be interpreted as an incoherent growth with compressive stresses perpendicular to the surface. Moreover, the Mn structure is found to switch from a sixfold in-plane symmetric 1 X 1 structure, which probably corresponds to strained fcc gamma-Mn, to a sixfold in-plane symmetric square-root 3 X square-root 3-30-degrees structure with in-plane lattice parameter a = 4.69 angstrom. This structural change occurs at a critical thickness of 5-6 monolayers, after the partial relaxation of the Mn in-plane lattice parameter. An analysis of the three-dimensional contribution to the RHEED patterns shows that the square-root 3 X square-root 3-30-degrees structure is probably identical to the Cu2Mg Laves phase which in turn closely resembles the alpha-Mn phase.