Spin-One Ising Model Including Biquadratic Interaction with Positive Coupling Constant

Abstract

Phase transitions of a spin-one Ising model with positive biquadratic interaction are investigated using a Monte Carlo method for a square lattice in comparison with the molecular-field results obtained from a two-sublattice model. Phase diagrams characterizing phase transitions of the model are presented for representative values of energy parameters and compared with those obtained from the molecular-field theory and other theories. It is shown that there exist no successive phase transitions as predicted from the molecular-field theory for any value of energy parameters we dealt with. Multicritical points on phase boundaries are estimated from the data to give reasonable values compared with those of other theories.