ON THE MEAN-FIELD THEORY OF MAGNETIC MULTILAYERS WITH BILINEAR AND BIQUADRATIC HEISENBERG EXCHANGE

A system consisting of several layers of magnetic ions interacting by both bilinear and biquadratic Heisenberg exchange is studied within th e framework of the mean-field approximation. It is shown that for S = 1 there exist two types of ordering: ferromagnetic and ferroquadrupola r. The stability of phases as the function cf temperature, biquadratic exchange and surface exchange is discussed analytically and numerical ly and it was shown that similar to bulk samples there appear first-an d second-order transitions and a tricritical point may appear dependin g on system parameters. (C) 1998 Elsevier Science B.V. All rights rese rved.