Surface first-order phase transitions in fcc Ising ferromagnets

The critical behavior of (111) surfaces in an fcc Ising ferromagnet is studied by means of the cluster variation method in the tetrahedron approximation. The critical value of the surface interaction ${\mathrm{J}}_{\mathrm{sc}}$ leading to a surface transition temperature larger than in the bulk is equal to 1.778${\mathrm{J}}_{\mathrm{b}}$. We find that the phase transition at the surface is of first order for a finite range of ${\mathrm{J}}_{\mathrm{s}}$>${\mathrm{J}}_{\mathrm{sc}}$. Results for the phase diagram and the temperature dependence of the magnetization and of the magnetic susceptibility are presented.