The compressible Ising-like model of Larkin and Pikin is equivalent to a constrained Ising model, as was recently shown by Sak. I introduce finite pressure effects into this system and find that the Ising transition is first order at low pressures and second order "renormalized" at high pressures. The tricritical pressure is equal to the rigidity modulus for the model, but will be lower for more realistic systems. The spherical tricritical point and Gaussian tetracritical point are also observable in principle as the pressure is varied.

• Received 4 September 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.1304