Magnetism of atomically thin fcc Fe overlayers on an expanded fcc lattice

We present experimental data on the magnetic properties of atomically thin fcc (γ-phase) Fe films (1-6 atomic layer nominal thickness) epitaxially grown on (Formula presented) obtained by linear magnetic dichroism in the angular distribution of Fe (Formula presented) core photoelectrons excited by linearly polarized synchrotron radiation. The sign and magnitude of the Fe (Formula presented) photoemission magnetic asymmetry indicates the onset of in-plane ferromagnetism at 2.5(2) monolayer (ML) thickness of γ-Fe. The Curie temperature is 288(2) K for 4 ML thickness. The magnetic splitting of the Fe (Formula presented) core hole sublevels is 1.10(2) eV, i.e., the same value as measured for a bcc-Fe(100) surface where large surface and near-surface enhanced moments contribute. These results characterize the epitaxial γ-Fe on (Formula presented) as a high-spin ferromagnet for thickness up to 4 ML, with an average magnetic moment per iron atom of 2.5(1)(Formula presented) A phase transition occurs between 4 and 5 ML thickness: the magnetic order of the pseudomorphic γ-Fe film decreases consistently with the breaking into two phases with the deeper layers in a low-spin and/or antiferromagnetic phase and surface restricted ferromagnetism, similar to the case of γ-Fe/Cu(100).