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 (R HEED) are used to study the structure and growth of epitaxial Co/Mn su perlattices on hcp (0001) Ru buffer layers. Mn deposited on fcc (111) or hcp (0001) Co presents a singular growth behavior which can be inte rpreted as an incoherent growth with compressive stresses perpendicula r to the surface. Moreover, the Mn structure is found to switch from a sixfold in-plane symmetric 1 X 1 structure, which probably correspond s to strained fcc gamma-Mn, to a sixfold in-plane symmetric square-roo t 3 X square-root 3-30-degrees structure with in-plane lattice paramet er a = 4.69 angstrom. This structural change occurs at a critical thic kness of 5-6 monolayers, after the partial relaxation of the Mn in-pla ne lattice parameter. An analysis of the three-dimensional contributio n to the RHEED patterns shows that the square-root 3 X square-root 3-3 0-degrees structure is probably identical to the Cu2Mg Laves phase whi ch in turn closely resembles the alpha-Mn phase.