  The indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between on-site
magnetic impurities is studied for two kinds of graphene nanoflakes consisting
of approximately 100 carbon atoms, posessing either zigzag or armchair edge.
The tight-binding Hamiltonian with Hubbard term is used in non-perturbative
calculations of coupling between the impurities placed at the edge of the
structure. In general, for zigzag-edged nanoflakes a pronounced coupling robust
against charge doping is found, while for armchair-edged structures the
interaction is weaker and much more sensitive to charge doping. Also the
distance dependence of indirect exchange differs significantly for both edge
forms.
