Magnetic response in finite carbon graphene sheets and nanotubes

The electronic and magnetic properties of graphene sheets with armchair and zig-zag edges are investigated using the Hückel tight binding model in conjunction with the London approximation. It is observed that in the presence of a perpendicular external magnetic field, the nanographenes show a diamagnetic behavior exhibiting counter-clockwise ring currents. Topological defects such as vacancies, Stone-Wale transformations (bond rotations) and holes are introduced in the graphene sheets in order to enhance local paramagnetic ring currents. These ring currents produce a local magnetic moment perpendicular to the defective site. In addition, current flows in finite carbon nanotubes are investigated.