The performance of advanced magnetic tunnel junctions built of ferromagnetic (FM) electrodes and MgO as an insulating barrier depends decisively on the properties of the FM/insulator interface. Here we investigate interface formation between the Co-based Heusler compound Co2MnSi (CMS) and MgO by means of Auger electron spectroscopy, low-energy electron diffraction, and low-energy photoemission. The studies are performed for different annealing temperatures (TA) and MgO layer coverages (4, 6, 10, 20, and 50 ML). Thin MgO top layers (tMgO≤10 ML) show distinct surface crystalline distortions, which can only be partly healed out by annealing and, furthermore, lead to distinct adsorption of carbon species after the MgO surface is exposed to air. For tMgO&gt
10 ML, the MgO layer surface exhibits clearly improved crystalline structure and hence only marginal amounts of adsorbates. We attribute these findings to MgO misfit dislocations occurring at the interface, inducing further defects throughout the MgO layer for up to at least 10 ML. Furthermore, spin-polarized photoemission spectra of the CMS/MgO interface are obtained for MgO coverages up to 20 ML, showing a clear positive spin polarization near the Fermi energy (EF) in all cases. © 2013 American Physical Society.