Fe-Co alloys in the alpha phase are soft magnetic materials which have high
saturation inductions over a wide range of compositions. However, above ab
out 1250 K, an alpha to gamma phase transition occurs. The fcc-based, gamma
, high-temperature phase is paramagnetic at this temperature. In this work
the low-temperature ordered B2, or alpha', phase, as well as the disordered
bcc phase of FeCo alloys, have been studied with first-principles electron
ic-structure calculations using the layer Korringa-Kohn-Rostoker method. Th
e variation of moment with composition (Slater-Pauling curve) is discussed.
For equiatomic FeCo, interatomic exchange couplings are derived from first
principles. These exchange interactions are compared to those obtained for
pure Fe and Co, and are used within a mean-field theory to estimate the hy
pothetical Curie temperature of the alpha phase. (C) 1999 American Institut
e of Physics. [S0021-8979(99)76808-8].