Studies of the stoichiometrical variation of epitaxial Fe3(1-δ)O4 thin films

Using plasma-assisted molecular beam epitaxy, (MBE) films of iron oxide spinel phases of Fe_3(1-δ)O₄ 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 Verwey transition, a strong indicator of iron oxide stoichiometry which occurs in Fe₃ O₄ at ~123 K, is broadened and pushed downward in temperature with decreasing iron content (and is absent in γ-Fe ₂O₃). 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 O₂/Fe flux ratios) can produce a range of Fe_3(1-δ) O₄ “defect-spinels”