Wetting Phenomena in bcc Binary Alloys

We study the influence of the surface orientation on the wetting behavior of bcc binary alloys, using a semiinfinite lattice model equivalent to a nearest-neighbor Ising antiferromagnet in an external magnetic field. This model describes alloys that exhibit a continuous B2 A 2 order-disorder transition, such as FeAl or FeCo. For symmetry-breaking surfaces like (100), an effective ordering surface field g1=0 emerges. Such a field not only crucially affects the surface critical behavior at bulk criticality, but also gives rise to wetting transitions below the critical temperature Tc. Starting from the mean-field theory for the lattice model and making a continuum approximation, a suitable Ginzburg Landau model is derived. Explicit results for the dependence of its parameters (e.g., of g1) on the microscopic iInteraction constants are obtained. Utilizing these in conjunction with Landau theory, the wetting phase diagram is calculated.