Onset of magnetism in B2 transition metals aluminides

The onset of magnetism in B2 transition metals aluminides, specifically in the phase of disordered bcc Fe xAl1− x, Co xAl1− x, and Ni xAl1− x alloys, was investigated through ab initio calculations. The objective was to understand the electronic structure and magnetic properties of these materials, focusing on the role of defect structures in influencing magnetism. The calculations employed two methodologies: the coherent potential approximation for the disordered phase and the tight-binding linear muffin-tin orbital method for the ordered intermetallics. Results indicated that large local magnetic moments arise from transition metal antisite defects in FeAl and CoAl, corroborating existing experimental findings. Furthermore, the presence of vacancies on either sublattice was shown to amplify the magnetic moments by reducing charge transfer to the transition metal atom. Our studies concluded that disordered Fe–Al alloys exhibit ferromagnetic ordering across the studied composition range, whereas Co–Al systems displayed magnetic properties only at Co concentrations of 0.5 or greater.