paper

Two-Dimensional Heisenberg Model with Nonlinear Interactions

arXiv:cond-mat/0202506 · doi:10.1103/PhysRevE.66.016120

Abstract

We investigate a two-dimensional classical -vector model with a nonlinear interaction $(1 + \bsigma_i\cdot \bsigma_j)^p$ in the large-N limit. As observed for N=3 by Blöte {\em et al.} [Phys. Rev. Lett. {\bf 88}, 047203 (2002)], we find a first-order transition for and no finite-temperature phase transitions for . For , both phases have short-range order, the correlation length showing a finite discontinuity at the transition. For , there is a peculiar transition, where the spin-spin correlation length is finite while the energy-energy correlation length diverges.

7 pages, 2 figures in a uufile. Discussion of the theory for p = p_c revised and enlarged

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