Study of the confined Ising magnet with long-range competing boundary fields

摘要

We present extensive Monte Carlo simulations of the Ising film confined in an L x M geometry (L M) in the presence of long-range competing magnetic fields h(n) = h(1)(3) (n = 1, 2,..., L) which are applied at opposite walls along the M-direction. Due to the fields, an interface between domains of different orientations that runs parallel to the walls forms and can be located close to one of the two surfaces or fluctuate in the centre of the film (localization-delocalization transition). This transition is the precursor of the wetting phase transition that occurs in the limit of infinite film thickness (L 00) at the critical curve T-w(h(1)). For T < T-w(h(1)) (T >= T-w(h(1))) such an interface is bound to (unbound from) the walls.We study this transition by measuring the magnetization profiles across the sample and the distribution function of both the magnetization of the whole sample and that of the centre of the film as a function of temperature, T, or strength of the wall field, h(1). We obtain estimates of the size-dependent wetting 'critical' points that allow us to extrapolate to the thermodynamic limit. Using the results of these extrapolations, confirmed by independent measurements of the cumulant, we draw the phase diagram of the wetting transition with long-range surface fields.We show that, starting from a localized interface well inside the non-wet phase, the position of the interface diverges exponentially when approaching the transition point, in contrast to the power-law divergence observed in the case of short-range fields.The properties of the delocalized interface are also studied. Within the wet phase the width of the capillary waves broadens the observed interface profiles. The spectrum of capillary waves is cut off at large wavelengths by the correlation length, xi(parallel to), which scales like xi(parallel to) similar to L-2, similar to the short-range case. Additionally, the interface stiffness is obtained from the Fourier spectrum of the capillary waves.