Structure and morphology of epitaxial Cu/Co bilayers grown on Cu(111) with Pb as a surfactant

The use of Pb as a surfactant has been shown to improve the magnetic properties of ultrathin Co/Cu heterostructures grown on Cu(111): the thickness range of Co films displaying perpendicular magnetic anisotropy is extended and a complete antiferromagnetic coupling between them is made possible. In this work, we apply low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to study the growth of epitaxial Cu/Co bilayers on the Cu(111) surface precovered by one monolayer of Pb forming a (4×4) superstructure, aiming to understand the origin of their magnetic properties. A quantitative comparison of experimental LEED spectra shows that the Cu layers grow in the twinned fcc structure, the amount of twinning depending on the number of stacking faults in the Co films. STM images of the capping Cu layers show not more than two atomic levels simultaneously exposed. This morphology is similar to that of Co films, which grow in the layer-by-layer mode in the presence of Pb. The result is the formation of sharp interfaces that favour the interface contribution to the magnetic anisotropy and allow the growth of layers with well defined thicknesses.