NEAR-SURFACE LONG-RANGE ORDER AT THE ORDINARY TRANSITION - SCALING ANALYSIS AND MONTE-CARLO RESULTS

Motivated by recent experimental activities on surface critical phenom ena, we present a detailed theoretical study of the near-surface behav ior of the local order parameter m(z) in Ising-like spin systems. Spec ial attention is paid to the crossover regime between ''ordinary'' and ''normal'' transition in the three-dimensional semi-infinite Ising mo del, where a finite magnetic field H-1 is imposed on the surface which itself exhibits a reduced tendency to order spontaneously. As the the oretical foundation, the spatial behavior of m(z) is discussed by mean s of phenomenological scaling arguments, and a finite-size scaling ana lysis is performed. Then we present Monte Carlo results for m(z) obtai ned with the Swendsen-Wang algorithm. In particular the sharp power-la w increase of the magnetization, m(z)similar to H(1)z(perpendicular to )(1-eta)(ord), predicted fur a small H-1 by previous work of the autho rs, is corroborated by the numerical results. The relevance of these f indings for experiments on critical adsorption in systems where a smal l effective surface field occurs is pointed out.