Longitudinal-Random-Field Mixed Ising Model with Arbitrary Spins

The longitudinal-random-field mixed Ising model consisting of arbitrary spin values has been studied by the use of an effective field theory with correlations (EFT). The phase diagrams of systems with mixed spins: σ=1/2, S=1; σ=1/2, S=3/2 are plotted. Not only the discontinuity at T=0~K,is found when both longitudinal fields are trimodal distributed, but also the tricritical behavior is observed in these phase diagrams between the bimodal and trimodal distributions of longitudinal fields, which is different from the single-spin one. The appearance of tricritical point is independent of the coordination number and spin values.