Magnesium interdiffusion and surface oxidation in magnetite epitaxial films grown on MgO(100).

Epitaxial Fe3O4(001) thin films were grown on MgO(001) using molecular beam of Fe-57 at the oxygen partial pressure of about 1 x 10(-6) mbar. LEED pat terns indicated perfect growth with a p(1 x 1) reconstructed surface (as la beled with respect to the bulk unit cell of magnetite). In situ UHV convers ion electron Mossbauer spectroscopy (CEMS) was al,plied to investigate the film stoichiometry and composition. GEMS spectra taken for films in the 10 nm range revealed a magnesium rich magnetite MgxF3-xO4 phase formed at the MgO/Fe3O4 interface. Ex situ Mossbauer measurements proved that the magneti te surface oxidizes when exposed to the atmosphere for a couple of weeks. T he oxidized phase was identified as a few nanometers thick surface layer of gamma -Fe2O3 formed on Fe3O4. By virtue of the gamma -Fe2O3 GEMS pattern, the oxidation can be easily misinterpreted as a surface non-stoichiometry f or films studied only ex situ. The oxidation process is reversible and anne aling at 600 K in UHV restores the magnetite surface structure. At elevated annealing temperature Fe also diffuses into MgO forming a wustite phase. ( C) 2001 Elsevier Science Ltd. All rights reserved.