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 oxide spinel phases of Fe-3(1-delta)O-4 type have been grown on single crystal MgO(100). Stoichiometry was controlled by variation of growth parameters, including substrate temperature, oxygen flux, plasma power, and deposition rate. Structural and magnetic studies of these films have been performed using SQUID magnetometry and x-ray diffraction (XRD). The temperature dependence of the Ver-wey transition, a strong indicator of iron oxide stoichiometry which occurs in Fe3O4 at similar to 123K, is broadened and pushed downward in temperature with decreasing iron content (and is absent in gamma-Fe2O3). Lattice spacing, verwey response, and magnetic ordering show that stable growth over a broad range 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.''