We present the chemical and structural optimization of ultrathin magnetic oxide EuO films on silicon. By applying a controlled in situ passivation of the Si(001) surface with SiOx in the monolayer regime, metallic silicide contaminations at the interface can be effectively reduced down to a sub-monolayer coverage, as was carefully quantified by interface-sensitive hard x-ray photoemission spectroscopy. Heteroepitaxial growth of EuO on Si(001) is sustained for this ultrathin SiOx-passivation, and bulk-near magnetic properties are observed for the 4 nm-thin EuO films. Our successful combination of chemically and structurally optimized EuO/Si(001) heterostructures by ultrathin in situ SiOx passivation makes this system promising for an application as alternative spin functional tunnel contacts in spin-FETs.

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