  Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on
a square lattice are investigated by means of the quantum Monte Carlo method
with the continuous-time loop algorithm. It is found that the critical
concentration of magnetic sites is independent of the spin size S, and equal to
the two-dimensional percolation threshold. However, the existence of quantum
fluctuations makes the critical exponents deviate from those of the classical
percolation transition. Furthermore, we found that the transition is not
universal, i.e., the critical exponents significantly depend on S.

Disordered Systems and Neural Networks