  The performance of advanced magnetic tunnel junctions build of ferromagnetic
(FM) electrodes and MgO as insulating barrier depends decisively on the
properties of the FM/insulator interface. Here, we investigate interface
formation between the half-metallic 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
(t_MgO<=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 t_MgO> 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
in all cases.
