Wetting phenomena in bcc binary alloys

We study the influence of the surface orientation on the wetting behavior o f bcc binary alloys, using a semiinfinite lattice model equivalent to a nea rest-neighbor Ising antiferromagnet in an external magnetic field. This mod el describes alloys that exhibit a continuous B2-A2 order-disorder transiti on, such as FeAl or FeCo. For symmetry-breaking surfaces like (100), an eff ective ordering surface field g(1) not equal 0 emerges. Such a held not onl y crucially affects the surface critical behavior at bulk criticality, but also gives rise to wetting transitions below the critical temperature T-c. Starting from the mean-field theory for the lattice model and making a cont inuum approximation, a suitable Ginzburg-Landau model is derived. Explicit results for the dependence of its parameters (e.g., of g(1)) on the microsc opic interaction constants are obtained. Utilizing these in conjunction wit h Landau theory: the welting phase diagram is calculated.