Within the correlation length equality approach, introduced in previous papers, a spontaneous symmetry breaking phenomenon among the identical planes of a two-layer ferromagnetic Ising film is growing, according to which the divergence of the correlation length at the critical point is...

On the basis of an improved elaboration of the method already proposed by the present authors, the correlation length along a vertical section of a two-layer ferromagnetic Ising film is calculated for all T ⩾ Tc. As a by-product the critical curve is determined and a very interesting...