“…In the equivalent, integral operator version, the method has been applied to studies of thin magnetic films [20,21]. At the same time, great efforts were put into application of H-K method to higher spins problem [22,23]. In this area, both the pure spin models (containing the spins of the same kind), for instance the isotropic Blume-Emery-Griffiths model [24], as well as the mixed-spin systems [6,25] have been considered.…”