Layer relaxation and intermixing inFe∕Cu(001)studied by surface x-ray diffraction

Abstract

The structure of Fe films thermally deposited on Cu(001) was analyzed using surface x-ray diffraction in the coverage range between 6 and 8 monolayers. Based on the analysis of crystal truncation rod data measured at 120 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, i.e., below and above transition temperatures reported for ferro- and antiferromagnetic ordering, no changes of the interlayer spacings larger than about $\ifmmode\pm\else\textpm\fi{}0.015\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ are found. Within the Fe film these correspond to fcc Fe $(1.78\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})$, while the top-layer spacing is expanded by 3--5 % in agreement with previous low-energy electron diffraction studies. Lateral disorder of surface atoms as described by the Debye parameter indicates displacements of the top-layer positions up to $0.23\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ corresponding to zigzag displacements observed in the $p2mg$ $(2\ifmmode\times\else\texttimes\fi{}1)$ superstructure. The inherent large penetration depth of the x rays also allowed the study of the structure and composition of the buried $\mathrm{Fe}∕\mathrm{Cu}$ interface. The data indicate $\mathrm{Fe}\ensuremath{-}\mathrm{Cu}$ intermixing, where nearly 50% of a Fe (Cu) monolayer are exchanged. Four layers across the interface are significantly affected. About 30% of the first Fe (Cu) and up to 15% of the second Fe (Cu) layer is alloyed by Cu (Fe).