Growth and magnetism of ultrathin Fe films on Pt(100)

Abstract

The scanning tunneling microscopy, low energy electron diffraction, and surface magneto-optic Kerr effect are used to investigate the morphology, structure, and magnetism of ultrathin Fe films on a Pt(100) surface. At room temperature, the deposited Fe atoms exchange sites with the Pt atoms of the substrate, and then grow in a quasi layer-by-layer mode. The Fe films show in-plane anisotropy for all coverages (up to 7 ML). Annealing at $600\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ switches the easy magnetization axis from in-plane to perpendicular when the thickness is smaller than 5.2 ML. The coercivity increases gradually to its maximum at 3.3 ML and then decreases abruptly, accompanied with a surface structure transition from $(1\ifmmode\times\else\texttimes\fi{}1)$ to $\mathrm{c}(2\ifmmode\times\else\texttimes\fi{}2)$. These results demonstrate the formation of $\mathrm{Fe}\penalty1000-\hskip0pt\mathrm{Pt}$ $\mathrm{L}{1}_{0}$ and $\mathrm{L}{1}_{2}$ chemically ordered alloys and a phase transition between them. The atom exchange process is found to play a key role in the alloy formation at significantly reduced growth temperature.