Groupe de Physique Statistique

Molecular-beam-epitaxy-grown hexagonal Fe/Ru superlattices have been investigated by anomalous x-ray diffraction near the iron absorption K edge to inquire selectively into the structure of both the iron and the ruthenium sublattices. The data have been analyzed by comparing simulated and experimental spectra in k space at various wavelengths and by means of a difference Fourier-transform method that allows us to trace the iron density profile along the growth direction of the superlattice and then directly probe the Fe/Ru interface. From both methods we extract the interplanar spacing for Fe and Ru. We get cFe�4.11 and cRu�4.33. The value a�2.69 is the same for both sublattices. We can thus calculate the atomic volume of hexagonal Fe in the superlattice VFe�12.87 A3 which is expanded by 14% with respect to hcp Fe. This may explain the onset of ferromagnetism in this metastable hexagonal Fe phase.