Lattice relaxation and three-dimensional reflection high-energy electron-diffraction analysis of strained epitaxial Co/Mn superlattices

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Abstract
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 1×1 structure, which probably corresponds to strained fcc γ-Mn, to a sixfold in-plane symmetric √3×√3−30° structure with in-plane lattice parameter a=4.69 Å. 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 √3×√3−30° structure is probably identical to the Cu2Mg Laves phase which in turn closely resembles the α-Mn phase.

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