A bond-diluted Ising ferromagnet with first- and second-neighbour interactions

The authors studied the effects of second-neighbour interactions on the critical temperature of the bond-diluted Ising model within the framework of the decorated Ising model. A suitable second-neighbour bond problem can be formulated and solved in the annealed limit. This limit is known to be quite reliable for Ising models without competing interactions. Plots of the critical-temperature and zero-temperature magnetisation versus concentration are given for various ratios of the second to first neighbour exchange coupling. When this ratio is very small, but finite, there is a tail in the phase boundary.