SURFACE REENTRANCE IN THE SEMIINFINITE SPIN-1 ISING-MODELS

The critical behavior of the semi-infinite Blume-Capel and Blume-Emery -Griffiths models is investigated in the pair approximation of the clu ster variation method. Equations for bulk and surface order parameters and n.n. correlation functions are given, from which analytical expre ssions for the second order bulk and surface critical temperatures are derived. The phase diagrams of the Blume-Capel model are classified, and the existence of a surface first-order transition is discussed. Th is transition is shown to be, under certain conditions, slightly reent rant, and the behavior of the surface order parameters and correlation functions is given for such a case. The extension of our results to t he Blume-Emery-Griffiths model is briefly discussed.