Insituobservations 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 ggr;‐Mn, to a sixfold in‐plane symmetric sqrt;3×sqrt;3−30° structure with in‐plane lattice parametera=4.69 A˚. 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 sqrt;3×sqrt;3−30° structure is probably identical to the Cu2Mg Laves phase which in turn closely resembles the agr;‐Mn phase.
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