Correlation and chemical disorder in heusler compounds: A spectroscopical study

Abstract

The first part of this study deals with the effects of local electronic correlations and alloying on the properties of the Heusler compound Co2Mn1−xFexSi. The analysis has been performed by means of first-principles band-structure calculations based on the local approximation to spin-density functional theory (LSDA) as well as photoemission calculations within the one-step model of photoemission. Correlation effects are treated using the Dynamical Mean-Field Theory (DMFT) and the LSDA+U approach. The formalism is implemented within the Korringa-Kohn-Rostoker (KKR) Green’s function method. In satisfactory agreement with available experimental data the magnetic and spectroscopic properties of Co2Mn1−xFexSi are explained in terms of strong electronic correlations. In addition the correlation effects have been analyzed separately with respect to their static or dynamical origin. To achieve a quantitative description of the electronic structure of Co2Mn1−xFexSi both static and dynamic correlations must be treated on equal footing. Furthermore, we report on our investigation of the spin-dependent electronic structure of ordered NiMnSb as well as of the disordered NixMn1−xSb alloy system. As a first point we studied the magneto-optical Kerr effect in ordered NiMnSb to extract information on the bulk-related electronic structure of this compound. In addition the influence of chemical disorder on the unoccupied electronic density of states was investigated by use of the ab-initio Coherent Potential Approximation method. These results are used for a detailed discussion of spin-resolved Appearance Potential Spectroscopy measurements. Our theoretical approach describes the spectra as the fully relativistic self-convolution of the matrix-element weighted, orbitally resolved density of states. The analysis is completed by one-step photoemission calculations focusing on the surface electronic structure of ordered NiMnSb(001).