  The effective interaction between resonant magnetic Anderson impurities in
graphene, mediated by conduction electrons, is studied as a function of the
strength of the onsite energy level of the impurities and the amplitude of
coupling to conduction electrons. The sign and character of the interaction
depend on whether the impurities reside on the same or opposite sublattices.
For the same (opposite) sublattice, the potential interaction is attractive
(repulsive) in the weak coupling limit with $1/R^3$ dependence on the distance;
the interaction reverses sign and becomes repulsive (attractive) in the strong
coupling limit and displays $1/R$ behavior. The spin-exchange coupling is
ferromagnetic (antiferromagnetic) at both large and small distances, but
reverses sign and becomes anti-ferromagnetic (ferromagnetic) for intermediate
distances. For opposite sublattices, the effective spin exchange coupling is
resonantly enhanced at distances where the energy levels cross the Dirac
points.
