DISORDERED ISING SYSTEMS: CLUSTER APPROXIMATION
Institute for Condensed Matter Physics, National Academy of Sciences of UkraineSome magnetic or ferroelectric compounds with impurities or with random substitution of atoms lead in some approximation to Ising model with random interactions. The theory of disordered Ising model with the nearest neighbour interaction is presented in this lecture. In particular, order parameter and spin correlation functions of the model are calculated and investigated within a two-particle cluster approximation for both quenched and annealed cases. The approach yields the exact results for the one-dimensional system. The long-range interaction is taken into account in the mean field approximation.