Polarization effects in empty states at the Fe(100)-vacuum and Fe(100)-noble metal interfaces

Empty electron states in Fe-based systems have been studied by Inverse Photoemission spectroscopy excited by low energy polarized electrons. Along with bulk-like transitions, surface (or interface) features are clearly identified. Ultrathin epitaxial films, namely Fe/Au(100) and Ag/Fe(100), and the clean Fe(100) surface are considered as examples. In thin films, majority and minority quantum well states originated by the electron confinement within the overlayer are observed. For ferromagnetic films in the monolayer regime, data indicate an exchange splitting exceeding the bulk value. At the Fe(100)-vacuum interface image-potential derived surface states display an unexpected reversal of the ordering of the majority and minority levels. Spin resolution allows to unambiguously identify the spin character of the states.