Quantum to classical transition in the ground state of a spin-$S$   quantum antiferromagnet
  We study a frustrated spin-$S$ staggered-dimer Heisenberg model on square lattice by using the bond-operator representation for quantum spins, and investigate the emergence of classical magnetic order from the quantum mechanical (staggered-dimer singlet) ground state for increasing $S$. Using triplon analysis, we find the critical couplings for this quantum phase transition to scale as $1/S(S+1)$. We extend the triplon analysis to include the effect of quintet dimer-states, which proves to be essential for establishing the classical order (N\'eel or collinear in the present study) for large $S$, both in the purely Heisenberg case and also in the model with single-ion anisotropy. 
Bimla Danu and Brijesh Kumar
cond-mat.str-el