Electronic structure and magnetism of Fe3-xVxX (X=Si, Ga, and Al) alloys by the KKR-CPA method

We present first-principles charge- and spin-self-consistent electronic structure computations on the Heusler-type disordered alloys Fe3-xVxX for three different metalloids X = (Si, 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 Fe3-xVxSi show that V substitutes preferentially on the Fe(B) site, not on the Fe(A,C) site, in agreement with experiment. Furthermore, calculations have been carried out for Fe3-xVxX alloys (with x = 0.25, 0.50, and 0.75), together with the end compounds Fe3X and Fe2VX, and the limiting cases of a single V impurity in Fe3X and a single Fe(B) impurity in Fe2VX. We delineate clearly how the electronic states and magnetic moments at various sites in Fe3-xVxX evolve as a function of the V content and the metalloid valence. Notably, the spectrum of Fe3-xVxX (X = 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 Fe(B) impurities, may play a role in the anomalous behavior of the transport properties. The total magnetic moment in Fe3-xVxSi is found to decrease nonlinearly and the 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 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. [S0163-1829(99)11543-1].