Local atomic order and element-specific magnetic moments of Fe3Si thin films on MgO(001) and GaAs(001) substrates

We investigated the magnetic as well as the structural properties of ${\text{Fe}}_{3}\text{Si}$ films on $\text{GaAs}(001)\text{\ensuremath{-}}(4\ifmmode\times\else\texttimes\fi{}6)$, $\text{GaAs}(001)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}2)$, and MgO(001) by x-ray magnetic circular dichroism (XMCD) and M\"ossbauer spectroscopy. From the XMCD spectra we determine averaged magnetic moments of $1.3--1.6{\ensuremath{\mu}}_{\text{B}}$ per Fe atom on the different substrates by a standard sum-rule analysis. In addition, XMCD spectra have been calculated by using the multiple-scattering Korringa-Kohn-Rostoker method which allows the site-specific discussion of the x-ray spectra. The M\"ossbauer spectra show a highly ordered and stoichiometric growth of ${\text{Fe}}_{3}\text{Si}$ on MgO while the growth on both GaAs substrates is strongly perturbed, probably due to diffusion of substrate atoms into the ${\text{Fe}}_{3}\text{Si}$ film. Therefore, we have studied the influence of Ga or As impurities on the magnetic properties of ${\text{Fe}}_{3}\text{Si}$ by calculations using coherent-potential approximation within the Korringa-Kohn-Rostoker method. For selected impurity concentrations additional supercell calculations have been performed using a pseudopotential code (VASP).