Spin-polarised electronic structure of disordered BCC FeCo alloys from LCAO-CPA

Abstract

LCAO-CPA theory is applied to substitutionally disordered ferromagnetic BCC FeCo alloys. Calculations are based on charge and spin self-consistent LCAO parameters determined for the pure component metals within the local spin density functional theory. Effects of charge and spin self-consistency on the alloy magnetisation are treated in an ad hoc manner. Mechanisms determining the concentration dependence of the local magnetic moments are explained. The correlation of magnetic moment formation and maintenance of local charge neutrality is discussed. At Fe sites the exchange splitting is enhanced by a hybridisation-driven local reoccupation within the spin sub-bands. This causes the observed increase of the Fe moment by about 30%. Numerical results are presented for the saturation magnetisation, local magnetic moments, d-band population and specific heat coefficient as functions of concentration. Qualitative agreement was obtained with available experimental data. Numerical results for the concentration dependence of the total and component density of states are shown. Quite different degrees of disorder are found for both spin states. The majority spin states are typical rigid-band-like, whereas a strong influence of alloy disorder on the minority spin states is observed. This causes a strong broadening of the minority spin Bloch spectral functions and Fermi surface.