IrFe Superlattices: 3D Pseudomorphism of Fe on (111) F.c.c. Ir

This paper describes the preparation and study of FeIr superlattices grown by molecular beam epitaxy. The samples were characterised by RHEED measurements, x-ray diffraction (XRD) and near-edge x-ray absorption spectroscopy (XAS). Electron diffraction shows that the surface structure of Fe on Ir is hexagonal up to a critical thickness of 3 ML and that the growth occurs layer by layer. An original method of thickness calibration by XRD on a series of FeIr superlattices is presented, which allows a precise determination of the distance of Fe planes. XRD measurements are in agreement with a ABCABC stacking sequence in the Fe films. Polarisation-dependent Fe K near-edge XAS indicate that the close-packed structure of Fe films, both in the plane and perpendicular to the hexagonal plane, is maintained up to a thickness of 5 ML of Fe. The critical thickness for superlattices is therefore larger than that of a “free” Fe film.