Ising model for tricritical points in ternary mixtures

An Ising model with spin $S=1\mathrm{}$ at each lattice point which exhibits multiple tricritical points is presented. This is a generalization of the Blume-Emery-Griffiths model which was used for describing the tricritical point in ${\mathrm{He}}^3$-${\mathrm{He}}^4$ mixtures. The model is solved in the molecular-field approximation. It is found that its thermodynamic behavior near the tricritical point is in qualitative agreement with the thermodynamic behavior of ternary fluids near their tricritical points.