Theory of surface effects in binary alloys. IV. Ordering alloys with two ferromagnetic components

A theory of the surface concentration, spatial long-range order and magnetism for binary body-centered-cubic ordering alloys with ferromagnetic components is presented. It is a mean-field theory based on a model consisting of pairwise interactions between nearest neighbors only. We find that for an alloy AxB1-x with spains SA, SB and Ising exchange integrals JAA, JAB, and JBB, magnetism favors surface segregation of the I component if SI2JIITM, and (iii) JABJAA,JBB. It is found that in case (iii) there is a range of temperatures where the surface is magnetic whereas the bulk is paramagnetic. Also studied is the effect on the surface properties produced by allowing the chemical and magnetic interactions to be location dependent. It is found in general that the results are more sensitive to changes in the chemical interactions. The FeCo system is examined along these lines, and the results are compared with existing experimental data. © 1981 The American Physical Society.

VIVO