Electronic and magnetic properties of Heusler alloy Co2MnSi epitaxial ultrathin films facing a MgO barrier studied by x-ray magnetic circular dichroism

The electronic and magnetic states of an epitaxially grown full-Heusler alloy ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Si}$ (CMS) $1.1\mathrm{nm}$ (4 ML) thick ultrathin film and a CMS $50\text{‐}\mathrm{nm}$ -thick film both facing an epitaxial MgO(001) tunnel barrier were element-specifically studied by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The observed XAS and XMCD spectra revealed that both the CMS films were not oxidized. The Co and Mn spin magnetic moments for the 4 ML thick CMS film obtained by applying the sum rules were close to those for the $50\text{‐}\mathrm{nm}$ -thick one and the theoretical values for bulk CMS with the $L{2}_1$ structure. These results indicate that 4 ML thick CMS ultrathin films facing a MgO barrier still retain the electronic and magnetic states for the $L{2}_1$ structure.