MAGNETIC-PROPERTIES OF DISORDERED ISING SYSTEMS WITH VARIOUS PROBABILITY-DISTRIBUTIONS OF THE EXCHANGE INTEGRALS

The disordered Ising spin-1/2 systems on square and simple cubic latti ces are investigated with three types (the Handrich-Kaneyoshi's, the G aussian, and the rectangular) of probability distribution of the excha nge integrals. The general expressions of average magnetization for va rious distributions are derived by means of the differential operator technique. The Curie temperatures T-C of the systems are calculated wi th the use of the effective-held theory, the correlated effective-fiel d theory, and the improved correlated effective-field theory (ICEFT), respectively. The dependence of T-C upon the parameter Delta, characte rizing the fluctuation of the exchange integrals is given. It is obtai ned, under ICEFT, that for the case of the square lattice, these distr ibutions give almost the same results and no reentrant phenomena occur , while on the simple cubic lattice, the reentrant phenomena only exis t under the discrete distribution.