Journal of the Physical Society of Japan
Spin-One Ising Model with Nearest-Neighbour and Next-Nearest-Neighbour Interactions
Motoyuki Tanaka, Takeshi Kawabe
Abstract
Phase transitions of the spin-one Ising model with nearest-neighbour and next-nearest-neighbour interactions are investigated for a square lattice using a molecular-field theory and a Monte Carlo method. Special attention is paid to the effects of the biquadratic next-nearest-neighbour interaction on the phase transitions of the model. Phase diagrams characterizing types of phase transition are obtained for several values of the coupling constants. The existence of the multi-critical points and the successive phase transitions are also discussed in connection with these phase diagrams.