Ordering tendencies in fe-al alloys in magnetic and non-magnetic models

Effective (Ising model) pair interactions in Fe-Al alloys are calculated using the generalized perturbation method and the linear muffin tin orbitals-coherent potential approximation (LMTO-CPA) technique, for paramagentic, ferromagnetic and disordered local moments (DLM) models. The tendency of primary ordering to the B2 structure and secondary ordering to the DO3 structure is examined as a function of Fe concentration. We find that the tendency to B2 (CsCl) ordering decreases in sequence from the paramagnetic to the DLM and to the ferromagnetic model. The tendency to secondary ordering in the DO3 structure is strongest in the ferromagnetic model and increases with Fe concentration. Effects of charge transfer, alloy volume (per atom) and lattice relaxation on the ordering tendency are found to be much more important for the secondary than for primary ordering.