The effective formation energies of atomic defects in this B2 phase were calculated by combining statistical mechanics with ab initio density-functional electron theory within the local spin-density approximation and the generalized-gradient approximation to the exchange-correlation functional. The effect of magnetism was required in order to stabilize the system against the spontaneous formation of antistructure atoms; even in the stoichiometric case. The defects were antistructure atoms, and the effective energy for the formation of thermal antistructure atoms was much smaller than the effective formation energies for Fe or Co vacancies. The behavior of atomic defects in this system, which consisted of 2 quite similar constituents, appeared to be much simpler than that in B2 transition-metal aluminides which comprised quite dissimilar constituents.

Atomic Defects in FeCo - Stabilization of the B2 Structure by Magnetism. M.Neumayer, M.Fähnle: Physical Review B, 2001, 64[13], 132102 (4pp)