Structure and magnetism of Fe mono- and multi-layer systems as seen by conversion electron Mossbauer spectroscopy at atomic scale

The characteristic magnetic phenomena of ultrathin films are attributed to their reduced dimensionality and increased importance of the interfacial properties originated at their boundaries. The loss of nearest neighbor interactions at the interfaces, band hybridization, expansion or contraction of the atomic spacing occur, resulting in local changes of the energy band structure. Recent technical developments make it now possible to grow ultrathin films in a strictly layer-by-layer mode and to produce large areas of flat surfaces. Nevertheless, small structural perturbations in the local atomic configuration can still exist and result in significant changes of the global magnetic properties. Conversion Electron Mossbauer Spectroscopy (CEMS) determines the hyperfine interaction parameters which are sensitive to the arrangement at the atomic scale. In particular, depth selectivity at a monolayer level has been achieved in Fe films with one atomic;layer replaced by the Mossbauer isotope Fe-57. This contribution reviews the experimental work on magnetic phenomena of bcc, fee and hcp Fe ultrathin films (including monolayer and multilayer structures), epitaxially grown by condensation from molecular beam under ultrahigh vacuum conditions. Since the structural and magnetic information can be achieved by using one method only, Mossbauer spectroscopy is pointed out as being an extremely effective and convenient tool for such purposes.