The order parameter and critical behavior of the spin 1/2 Ising film

Using the effective field theory with a probability distribution technique that accounts for the self-spin correlations, we have studied the influence of surface defects on the critical properties of the magnetic spin Ising film. We discuss an L layer film of simple cubic symmetry with nearest-neighbor interactions in which the strengths of the interactions at the surfaces are different from the bulk value. We derive the phase diagram, the longitudinal susceptibility and the effective critical exponent in the case of perfect surface. In such films, the critical temperature can shift to either lower or higher temperature compared to the corresponding bulk value. In the case of surface with random interaction, it is found that the critical exponent β1 follows very closely that of the perfect surface case, and far from the critical temperature, the effective exponent decreases with increasing the concentration p.