STUDIES OF THE STOICHIOMETRICAL VARIATION OF EPITAXIAL FE-3(1-DELTA)O-4 THIN-FILMS

Using plasma-assisted molecular beam epitaxy, (MBE) films of iron oxid e spinel phases of Fe-3(1-delta)O-4 type have been grown on single cry stal MgO(100). Stoichiometry was controlled by variation of growth par ameters, including substrate temperature, oxygen flux, plasma power, a nd deposition rate. Structural and magnetic studies of these films hav e been performed using SQUID magnetometry and x-ray diffraction (XRD). The temperature dependence of the Ver-wey transition, a strong indica tor of iron oxide stoichiometry which occurs in Fe3O4 at similar to 12 3K, is broadened and pushed downward in temperature with decreasing ir on content (and is absent in gamma-Fe2O3). Lattice spacing, verwey res ponse, and magnetic ordering show that stable growth over a broad rang e of conditions results in stoichiometric Fe3O4, although variation of growth parameters (especially high O-2/Fe flux ratios) can produce a range of Fe-3(1-delta)O-4 ''defect-spinels.''