Surface Magnetism: a Monte Carlo Study of Surface Critical Behavior.

We study the critical behavior of the Ising and Heisenberg Models on a simple cubic lattice with two free surfaces using the Monte Carlo Method. The effect of both the ratio of surface to bulk coupling J_ {rm s}/J_{rm b}, and the length to width ratio, r = L/D, are considered. The internal energy, the magnetic susceptibility, and the specific heat near the critical point are calculated for both the surface and the bulk. Results indicate that there is a region of r values for which the critical coupling between spins on the surface, J_{rm sc}, can be less than 1.55J_{rm b}, contrary to what other authors have reported.