The Neel Temperature and Sublattice Magnetization for the Stacked Triangular-Lattice Antiferromagnet with a Weak Interlayer Coupling
The quantum Heisenberg antiferromagnet on the stacked triangular lattice with the intralayer nearest-neighbor exchange interaction J and interlayer exchange J' is considered within the non-linear -model with the use of the renormalization group (RG) approach. For J' J the asymptotic formula for the Neel temperature TNeel and sublattice magnetization are obtained. RG turns out to be insufficient to describe experimental data since it does not take into account the 2-vortices. Therefore TNeel is estimated using the Monte-Carlo result for the 2D correlation length  which has a Kosterlitz-type behavior near the temperature TKT where the vortices are activated.
A.N. Ignatenko et al., "The Neel Temperature and Sublattice Magnetization for the Stacked Triangular-Lattice Antiferromagnet with a Weak Interlayer Coupling", Solid State Phenomena, Vols. 152-153, pp. 257-260, 2009