The Monte Carlo simulation technique is used to study the phase diagrams of a two-dimensional spin-1 Ising model with bilinear and biquadratic nearest-neighbor pair interactions and a single-ion potential. A staggered quadrupolar phase appears at low temperatures with the competing bilinear and biquadratic interactions. The phase boundary line of the staggered quadrupolar phase and that of the ferromagnetic phase are extremely close to each other at low temperatures. An argument is used to distinguish the most probable phase diagram from the several possible ones based on the Monte Carlo data.

• Received 28 April 1987

DOI:https://doi.org/10.1103/PhysRevB.36.8945