Monte Carlo simulations of the pseudospin model of RbSCN

The microscopic Ising-like model of the order-disorder phase transition in improper ferroelastic crystals is presented. For such a system, the spin-st rain coupling can be written in terms of four-spin interactions. Three-dime nsional Monte Carlo simulation shows that for a certain strength of the fou r-spin interaction the system is close to the tricritical point. The calcul ated temperature dependence of the order parameter is in very good agreemen t with the experimental data for RbSCN. The results also show that the grow th of the size of precursor clusters is suppressed when approaching T-c fro m below, whereas the order parameter susceptibility is increasing.; This is in good agreement with the diffuse neutron scattering data on RbSCN and KS CN, which yield an increase of the diffuse intensity with increasing temper ature below T-c, whereas its width remains constant throughout the whole or dered phase. These results show that elastic effects can stabilize the prec ursor clusters at the order-disorder phase transition below T-c.