The quantum Heisenberg antiferromagnet on the square lattice
  The pure-quantum self-consistent harmonic approximation, a semiclassical method based on the path-integral formulation of quantum statistical mechanics, is applied to the study of the thermodynamic behaviour of the quantum Heisenberg antiferromagnet on the square lattice (QHAF). Results for various properties are obtained for different values of the spin and successfully compared with experimental data. 
A.Cuccoli, V.Tognetti, P. Verrucchi, R.Vaia