PUB - Publikationen an der Universität Bielefeld

A detailed understanding of ultrathin film surface properties is crucial for the proper interpretation of spectroscopic, catalytic, and spin-transport data. We present x-ray magnetic circular dichroism (XMCD) and x-ray resonant magnetic reflectivity (XRMR) measurements on ultrathin Fe3O4 films to obtain magnetic depth profiles for the three resonant energies corresponding to the different cation species Fe^2+_oct, Fe^3+_tet , and Fe^3+_oct located on octahedral and tetrahedral sites of the inverse spinel structure of Fe3O4. By analyzing the XMCD spectrum of Fe3O4 using multiplet calculations, the resonance energy of each cation species can be isolated. Performing XRMR on these three resonant energies yields magnetic depth profiles that each correspond to one specific cation species. The depth profiles of both kinds of Fe^3+ cations reveal a (3.9 ± 1.0)-Å-thick surface layer of enhanced magnetization, which is likely due to an excess of these ions at the expense of the Fe^2+_oct species in the surface region. The magnetically enhanced Fe^3+_tet layer is additionally shifted about 2.9 ± 0.4 Å farther from the surface than the Fe^3+_oct layer.