Spin-polarized conduction in localized ferromagnetic materials: The case of Fe3O4 on MgO(100)

The surface electronic structure of 1500-Å-thick Fe3O4(100) films has been investigated by spin-resolved photoemission spectroscopy with vacuum ultraviolet synchrotron radiation. The films, epitaxially grown on MgO(100) substrates using plasma-assisted molecular-beam deposition, are briefly exposed to air during transfer to the photoemission chamber. It is shown that clean surfaces of Fe3O4 films after exposure to air can be recovered through mild annealing in an oxygen atmosphere. The presence of the characteristic Verwey transition, as detected in the valence-band photoemission spectra, provides evidence for the excellent electronic quality at the surface of these films. The top of the valence band is found to be negatively spin polarized, with a value of ≈−50%; this result strongly points towards the localized nature of the 3d states in this system.