STRUCTURAL-PROPERTIES OF (100)FE/IR SUPERLATTICES

The structure of Fe layers in Fe/Ir superlattices, prepared by molecular beam epitaxy with varying thicknesses of each constituant, has been investigated by X-ray absorption spectroscopy. Taking advantage of the linear polarisation of the X-ray beam, structural anisotropy has been determined in the growth direction and the direction perpendicular to it. Layers of Fe epitaxied on Ir display a body centered tetragonal structure for thicknesses around 1 nm, while a strained body centered cubic structure is observed for larger Fe layers. For very low thicknesses, unambiguous results on the Fe structure cannot be derived from the present data. The evolution of the lattice parameters of Fe was measured. Comparison of experimental spectra with calculated ones, taking into account multiple scattering effects, was also performed. The growth model, deduced from these measurements, implies a 45 degrees rotation of the Fe square lattice with respect to that of Ir which is square-centered in the (100) plane.