The mechanism of magnetism in stacked nanographite: theoretical study

Nanographite systems, where graphene sheets of dimensions of the order of nanometres are stacked, show novel magnetic properties, such as spin-glass-like behaviours and change of electron spin-resonance linewidths in the course of gas adsorptions. We investigate stacking effects in zigzag nanographite sheets theoretically, by using a tight-binding model with Hubbard-like on-site interactions. We find a remarkable difference in magnetic properties between the simple A-A-type and A-B-type stackings. For the simple stacking, there are no magnetic solutions. For the A-B stacking, we find antiferromagnetic solutions for strong on-site repulsions. The local magnetic moments tend to exist at the edge sites in each layer due to the large amplitudes of the wavefunctions at these sites. Relations with experiments are discussed.