Stoichiometric Fe3O4 films have formed epitaxially on α-Al2O3 and MgO single-crystal substrates by a reactive vapor deposition method. In order to apply conversion electron Mössbauer spectroscopy depth-selectively, a 5-7 Åthick probe layer containing 57Fe was formed at various depths in inactive 56Fe3O4 matrix films. At the topmost surfaces and also at the interfaces, the essential electronic features of bulk Fe3O4 are retained, including a rapid electron hopping between the Fe2+ and Fe3+ ions at B sites. Minor depth-dependent changes are confined to a few outermost atomic layers, and the changes depend on the orientation and the lattice mismatch with the substrate. For (111) growth on α-Al2O3, the surface layer seems to be strongly relaxed to reduced the electric polarization, while a high density of defects seems to be concentrated at the interface with α-Al2O3. For (001) growth on MgO, the surface retains the spinel lattice though slightly oxidized, while the interface with MgO has good crystallinity and stoichiometry. An enhanced thermal fluctuation of the Fe3+-spins in contact with the MgO substrate and in the topmost surface layer can be seen in their reduced magnetic hyperfine field at 300 K.
ASJC Scopus subject areas
- Condensed Matter Physics