A Monte Carlo study of thin spin-1 Ising films with surface exchange enhancement

Using extensive Monte Carlo simulations the effect of surface exchange enha ncement on ultrathin spin-1 Ising films (having simple cubic symmetry) rang ing in thickness from L = 3 to 8 atomic layers, has been studied. The simul ations were performed on systems containing up to just over 15000 spins wit h periodic boundary conditions imposed in directions perpendicular to the h im thickness. Within the resolution of the Monte Carlo data, it was conclud ed that the ratio of surface to bulk exchange interaction strengths, J(s)/J (b))(crit), at which the critical temperatures of the film and bulk materia l were equal, was independent of L, as predicted by mean field and effectiv e field theories. However, the value of J(s)/J(b))(crit) is spin dependent. It was found that for the spin-1 Ising films, J(s)/J(b))(crit) = 1.45, sig nificantly below the value 1.52 obtained by Monte Carlo simulation for the spin 1/2 system reported in the literature. (C) 2000 Elsevier Science B.V. All rights reserved. rights reserved.