Mössbauer Spectroscopic Study of Surface and Interface Properties of Epitaxial Fe₃O₄ Films

Stoichiometric Fe3O4 films have been epitaxially formed on both =α-Al2O3 and MgO single-crystalline substrates by a reactive vapor deposition method. A few-A-thick probe layer containing 57Fe was formed at a desired depth of an inactive S6Fe3O4 matrix film to apply a depth selective Mossbauer spectroscopy. Even at the topmost layer and also at the interface, the electronic state retained the essential features of Fe304 bulk so that the Verwey transition was clearly detected. Any minor depth-dependent changes in electronic state were confined in a few outermost atomic layers. The nature of the changes depended on the orientation of the films and the lattice mismatch between the substrate and the film.