  I use the two-step density-matrix renormalization group method to extract the
critical exponents $\beta$ and $\nu$ in the transition from a N\'eel
$Q=(\pi,\pi)$ phase to a magnetically disordered phase with a spin gap. I find
that the exponent $\beta$ computed from the magnetic side of the transition is
consistent with that of the classical Heisenberg model, but not the exponent
$z\nu$ computed from the disordered side. I also show the contrast between
integer and half-integer spin cases.
