Exact Surface-Layer Magnetization of 2D Ising Models with Alternately Layered Exchange Interactions and Alternate Surface Magnetic Field —Reentrant Phenomena at Surfaces—

Abstract

The two-dimensional half-plane Ising model is examined in the presence of the alternately layered exchange interactions or the alternate surface magnetic field. Special attention is paid to the effect of the frustration or the competing interactions on the free energy and the magnetization. Especially, the surface-layer magnetization is calculated exactly. For some conditions, after the onset of the magnetic ordering at bulk T_c, the surface-layer spontaneous magnetization is shown to decrease exponentially toward zero as T→0. These models offer examples of the reentrant phenomena at surfaces.