Tricritical behavior in the mixed spin- and spin-1 Ising ferromagnetic system on the two-fold Cayley tree

The ferromagnetic mixed spin- and spin-1 Ising system with a crystal-field interaction is studied within the framework of the exact recursion relations on the two-fold Cayley tree. The effect of the coordination number on the phase diagrams is investigated. The tricritical point has been observed in our calculations for q 5. The results are compared with those of other approximate methods.