Emission Mossbauer spectroscopy study of the Fe3O4(100) surface and Fe3O4/MgO(100) and Fe3O4/CoO(100) interfaces -: art. no. 165407

Co-57 probe atoms were deposited on the surface of Fe3O4(100) films grown on MgO(100) substrates. In situ emission Mossbauer spectroscopy and reflection high-energy electron-diffraction measurements were performed on the surface after the deposition and after an annealing at 250 degreesC. After the deposition, the probe atoms are in Fe2+ and Fe3+ charge states in a disordered atomic arrangement at the surface. They do not participate in the electron-exchange process that takes place in the bulk part of the film. After annealing at 250 degreesC the probe atoms partly diffuse below the surface. All of the probe atoms now participate in the electron-exchange process. We observed enhanced fluctuations of the spins at and close to the surface at room temperature. Deposition of a MgO layer on top of the magnetite film significantly reduces the spin fluctuations. At 130 K the probe atoms at the Fe3O4/MgO interface are in a Fe3+ charge state. Deposition of CoO on a magnetite film results in an interface that consists of a cobalt substituted magnetite layer (CoxFe3-xO4). We estimate the cobalt content of this interface layer to be 0.5+/-0.1.