Structural and magnetic investigation of the interfaces of Fe3O4/MgO(001) with and without NiO interlayer

We present an investigation on the structural and magnetic properties of the interfaces of Fe3O4/MgO(001) and Fe3O4/NiO/MgO(001) by extracting cation-selective magneto-optical depth profiles by means of x-ray resonant magnetic reflectivity in combination with charge-transfer multiplet simulations of x-ray magnetic circular dichroism data. For Fe3O4/MgO(001), the magneto-optical depth profiles at the Fe-oct(2+) and the Fe-oct(3+) resonant energies follow exactly the structural profile, while the magneto-optical depth profile at the Fe-tet(3+) resonance is offset by 3.2 +/- 1.3 angstrom from the interface, consistent with a B-site interface termination of Fe3O4 with fully intact magnetic order. In contrast, for Fe3O4/NiO(001), the magneto-optical depth profiles at the Fe2+ oct and the Ni2+ resonances agree with the structural profile, but the interface positions of the magneto-optical depth profiles at the Fe-oct(2+) and the Fe-tet(3+) resonances are spatially shifted by 3.3 +/- 1.4 and 2.7 +/- 0.9 angstrom, respectively, not consistent with a magnetically ordered stoichiometric interface. This may be related to an intermixed (Ni, Fe)O layer at the interface. The dichroic depth profile at the Ni L-3 edge might hint at uncompensated magnetic moments throughout the NiO film.