  We describe a Monte Carlo simulation study of the magnetic phase diagram of
diluted magnetic semiconductors doped with shallow impurities in the low
concentration regime. We show that because of a wide distribution of
interaction strengths, the system exhibits strong quantum effects in the
magnetically ordered phase. A discrete spin model, found to closely approximate
the quantum system, shows long relaxation times, and the need for specialized
cluster algorithms for updating spin configurations. Results for a
representative system are presented.
