  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.

Strongly Correlated Electrons