  We used a quantum Monte Carlo method to study the magnetic impurity adatoms
on graphene. We found that by tuning the chemical potential we could switch the
values of the impurity's local magnet moment between relatively large and small
values. Our computations of the impurity's spectral density found its behavior
to differ significantly from that of an impurity in a normal metal and our
computations of the charge-charge and spin-spin correlations between the
impurity and the conduction band electrons found them to be strongly
suppressed. In general our results are consistent with those from poor man's
scaling and numerical renormalization group methods.
