  Using the tight-binding approximation we calculated the magnetic
susceptibility of graphene quantum dots (GQD) of different geometrical shapes
and sizes, smaller than the magnetic length, when the magnetic properties are
governed by the electron edge states. Two types of edge states can be
discerned: the zero-energy states (ZES) located exactly at the zero-energy
Dirac point, and the dispersed edge states (DES) with the energy close, but not
exactly equal to zero. DES are responsible for the temperature independent
diamagnetic response, while ZES provide the temperature dependent spin Curie
paramagnetism. The hexagonal, circular and randomly shaped GQDs contain mainly
DES and, as a result, they are diamagnetic. The edge states of the triangular
GQDs are ZES and these dots reveal the interplay between the spin
paramagnetism, dominating for small dots and at low temperatures, and bulk
orbital diamagnetism, dominating for large dots and at high temperatures.
