Abstract
A detailed characterization of magnetic oxide films is essential to enable their use in magnetoresistive devices since their properties depend critically on stoichiometry and structural order. Here, the composition and magnetic properties of ultrathin iron oxide films grown epitaxially on Al2O3(0001) have been characterized using x-ray magnetic circular dichroism XMCD and magnetoresistance (MR) measurements. The XMCD data show by comparison with theoretical calculations that we have successfully found growth conditions for well ordered epitaxial films with Fe3O4 stoichiometry. Nonstoichiometric films exhibit, in addition to a relative reduction in Fe2+ ions, a net transfer of Fe3+ from tetrahedral to octahedral sites. The in-plane MR for both these films is found to be 1% at room temperature in a field of 1 T even though the electrical conductivity differs by a factor of 5.
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