Effects of the next-nearest-neighbor interaction on the phase transition of magnetic multilayers

Based on Ising model, the effects of nearest and next-nearest neighbor interactions on the magnetic properties of films with BCC structure have been studied by an improved 4×4 transfer matrix method. The dependence of the phase transition temperature TCon both the ratio of surface coupling to bulk one Js/JBand the next-nearest coupling to nearest one b and the size of the system are studied. It is found that there exists a multicritical value Js/JB (JC) at which the phase transition temperature TCat the surface is the same as that in the body. The dependence of JCon the value of bfor different number of surface layers is also studied. The calculated results are well consistent with the experimental facts.