Electronic structure and magnetism ofFe3−xVxX(X=Si,Ga, and Al) alloys by the KKR-CPA method

Abstract

We present first-principles charge- and spin-self-consistent electronic structure computations on the Heusler-type disordered alloys ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ for three different metalloids $X=(\mathrm{Si},\mathrm{Ga},$ and Al). In these calculations we use the methodology based on the Korringa-Kohn-Rostoker formalism and the coherent-potential approximation generalized to treat disorder in multicomponent complex alloys. Exchange correlation effects are incorporated within the local spin density approximation. Total energy calculations for ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Si}$ show that V substitutes preferentially on the $\mathrm{Fe}(B)$ site, not on the $\mathrm{Fe}(A,C)$ site, in agreement with experiment. Furthermore, calculations have been carried out for ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ alloys (with $x=0.25,$ $0.50,$ and $0.75),$ together with the end compounds ${\mathrm{Fe}}_{3}X$ and ${\mathrm{Fe}}_{2}\mathrm{V}X,$ and the limiting cases of a single V impurity in ${\mathrm{Fe}}_{3}X$ and a single $\mathrm{Fe}(B)$ impurity in ${\mathrm{Fe}}_{2}\mathrm{V}X.$ We delineate clearly how the electronic states and magnetic moments at various sites in ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ evolve as a function of the V content and the metalloid valence. Notably, the spectrum of ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}X$ $(X=\mathrm{Al}$ and Ga) develops a pseudogap for the majority as well as minority spin states around the Fermi energy in the V-rich regime, which, together with local moments of $\mathrm{Fe}(B)$ impurities, may play a role in the anomalous behavior of the transport properties. The total magnetic moment in ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Si}$ is found to decrease nonlinearly, and the $\mathrm{Fe}(B)$ moment to increase with increasing x; this is in contrast to expectations of the ``local environment'' model, which holds that the total moment should vary linearly while the $\mathrm{Fe}(B)$ moment should remain constant. The common-band model, which describes the formation of bonding and antibonding states with different weights on the different atoms, however, provides insight into the electronic structure of this class of compounds.