We study the influence of pentagons and heptagons, dislocations, and other topological defects breaking the sublattice symmetry on the magnetic properties of a graphene lattice. It is known that vacancies and other defects involving uncoordinated atoms induce localized magnetic moments in the lattice. Within the Hubbard model the total spin of the nonfrustrated lattice is equal to the number of uncoordinated atoms for any value of the Coulomb repulsion $U$ according to the Lieb theorem. With an unrestricted Hartree-Fock calculation of the Hubbard model we show that the presence of a single pentagonal ring in a large lattice is enough to alter the standard behavior and a critical value of $U$ is needed to get the polarized ground state. Dislocations, Stone-Wales, and similar defects are also studied.

• Received 22 December 2008

DOI:https://doi.org/10.1103/PhysRevB.79.075413