Magnetic behaviour of Ising multilayers

The magnetic behavior of Ising multilayer system including nearest neighbor and next nearest neighbor interactions is investigated by use of variation al cumulant expansion (VCE) method. The formulae for spontaneous magnetizat ion, coercivity, Curie point, Neel point, susceptbility and molecular field parameters responding to the number of layers are deduced and discussed nu merically. It is exactly demonstrated that, in 2-dimensional and 3-dimensio nal systems, the spontaneous magnetization calculated by first order of the VCE is the same as the results of mean field theory. This means that the f irst order of VCE is valid in low temperature. The validity of VCE in high temperature (above the critical point) is explained by the physical meaning of VCE method.