We study the thermodynamics of the spin-S two-dimensional quantum Heisenberg antiferromagnet on the square lattice with nearest (J1) and next-nearest (J2) neighbor couplings in its collinear phase (J2/J1>0.5), using the pure-quantum self-consistent harmonic approximation. Our results show the persistence of a finite-temperature Ising phase transition for every value of the spin, provided that the ratio J2/J1 is greater than a critical value corresponding to the onset of collinear long-range order at zero temperature. We also calculate the spin- and temperature-dependence of the collinear susceptibility and correlation length, and we discuss our results in light of the experiments on Li2VOSiO4 and related compounds.
Cite
@article{arxiv.cond-mat/0312050,
title = {Ising transition in the two-dimensional quantum $J_1-J_2$ Heisenberg model},
author = {Luca Capriotti and Tommaso Roscilde and Andrea Fubini and Valerio Tognetti},
journal= {arXiv preprint arXiv:cond-mat/0312050},
year = {2007}
}