THERMAL-BEHAVIOR OF THE PLANAR SPIN CHAIN WITH COMPETING INTERACTIONS UP TO 3RD NEIGHBORS

The 1 D classical planar model with competing interactions up to third neighbours is exactly studied at finite temperature by the transfer matrix method. The third neighbour interaction enters first an second order phase transition and full frustration lines at zero temperature. In particular, we have studied the static structure factor S(q) to understand the finite temperature short range order (SRO). This results strictly related to the zero temperature long range order (LRO) and coexistence of SRO configurations in the neighborhood of the zero temperature first order transition lines is clearly demonstrated. We have also found the signal of the full frustration of our model in a two equal weight peaks profile of S(q) in the neighborhood of the ferro-antiferromagnetic boundary on which the chain breaks itself at zero temperature in two ferromagnetic sublattices the angle in between being arbitrary. © 1990 Springer-Verlag.