Thin Ising films with competing walls: A Monte Carlo study

摘要

Ising magnets with a nearest neighbor ferromagnetic exchange interaction J on a simple cubic lattice are studied in a thin film geometry using extensive Monte Carlo simulations. The system has two large L x L parallel free surfaces, a distance D apart from each other, at which competing surface fields act, i.e., HD=-H1. In this geometry, the phase transition occurring in the bulk at a temperature Tcb is suppressed, and instead one observes the gradual formation of an interface between coexisting phases stabilized by the surface fields. While this interface is located in the center of the film for temperatures Tc(D)0 (and the total magnetization is negative). As predicted, for large D this transition temperature Tc(D) is close to the wetting transition Tw(H1) of the semi-infinite system, but the transition nevertheless has a two-dimensional Ising character. Due to crossover problems (for D--> [infinity] the width of the asymptotic Ising region shrinks to zero, and one presumably observes critical wetting in this model) this Ising nature is clearly seen only for rather thin films. For Tc(D)