Iron vacancy ordered γ-Fe2O3(001) epitaxial films:: The crystal structure and electrical resistivity

We report the structural characterization and transport properties of highly-ordered epitaxial gamma-Fe2O3 thin films grown by a pure ozone-assisted molecular beam epitaxy method. X ray diffraction (XRD) measurements at a synchrotron facility indicated that the composition of films was close to that of gamma-Fe2O3 with Fe vacancy only occurring at octahedral sites of a spine]. We revealed that the crystal symmetry was reduced from a cubic, giving rise to extra superlattice reflections along the c* axis and this showed good agreement with a tetragonal structure with c less than or similar to 3a. We succeeded in determining the position of vacancy sites as well as the unit cell by comparing the XRD results with calculated reflection patterns for plausible vacancy ordered models. The temperature dependent resistivity of the vacancy ordered gamma-Fe2O3 was several orders higher than that of Fe3O4.