Chemical ordering in the first stages of Co-Pt film growth on Pt(111)

Abstract

The first stages of the growth of ${\mathrm{Pt}}_{C}{\mathrm{Co}}_{1\ensuremath{-}C}$ films on Pt(111) were investigated in situ by x-ray reflectometry and grazing incidence x-ray diffraction. Co-Pt ultrathin alloys are among the most interesting candidates for magneto-optic recording media. In this study we show that, at a given substrate temperature, a surface-induced equilibrium state is established since the very beginning, resulting in a bilayer where Pt segregates on top of a Co-rich buried layer. The sample obtained by codeposition of about 1 monolayer ${\mathrm{Pt}}_{20}{\mathrm{Co}}_{80}$ at 520 K was studied in details. Its structure was solved by quantitative analysis of the intensity distribution of crystal truncation rods. The outermost plane contains at least 80 at. % Pt, while the buried one is Co rich, with a concentration that is also close to 80%. No significant Co diffusion in the underlying substrate layers was observed. The stacking was found fcc in coherent continuation with the substrate. We believe that the growth mechanism observed here is responsible for clustering in Pt-rich films with perpendicular magnetic anisotropy.