Magnetism of atomically thin fcc Fe overlayers on an expanded fcc lattice:Cu84Al16(100)

Abstract

We present experimental data on the magnetic properties of atomically thin fcc (\ensuremath{\gamma}-phase) Fe films (1--6 atomic layer nominal thickness) epitaxially grown on ${\mathrm{Cu}}_{84}{\mathrm{Al}}_{16}(100)$ obtained by linear magnetic dichroism in the angular distribution of Fe $3p$ core photoelectrons excited by linearly polarized synchrotron radiation. The sign and magnitude of the Fe $3p$ photoemission magnetic asymmetry indicates the onset of in-plane ferromagnetism at 2.5(2) monolayer (ML) thickness of \ensuremath{\gamma}-Fe. The Curie temperature is 288(2) K for 4 ML thickness. The magnetic splitting of the Fe $3p$ $\mathrm{mj}$ 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 \ensuremath{\gamma}-Fe on ${\mathrm{Cu}}_{84}{\mathrm{Al}}_{16}(100)$ as a high-spin ferromagnet for thickness up to 4 ML, with an average magnetic moment per iron atom of 2.5(1)${\ensuremath{\mu}}_{B}.$ A phase transition occurs between 4 and 5 ML thickness: the magnetic order of the pseudomorphic \ensuremath{\gamma}-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 \ensuremath{\gamma}-Fe/Cu(100).