We study the influence of pentagons, dislocations and other topological defects breaking the sublattice symmetry on the magnetic properties of a graphene lattice in a Hartree Fock mean field scheme. The ground state of the system with a number of vacancies or similar defects belonging to the same sublattice is known to have total spin equal to the number of uncoordinated atoms in the lattice for any value of the Coulomb repulsion U according to the Lieb theorem. We show that the presence of a single pentagonal ring in a large lattice is enough to alter this behavior and a critical value of U is needed to get the polarized ground state. Glide dislocations made of a pentagon-heptagon pair induce more dramatic changes on the lattice and the critical value of U needed to polarize the ground state depends on the density and on the relative position of the defects. We found a region in parameter space where the polarized and unpolarized ground states coexist.

5 pages, 3 figures