Curvature Effects on the Magnetism of Ultrashort Zigzag Carbon Nanotubes and Nanographenes

The curvature effects on the magnetic properties of finite-length zigzag carbon nanotubes and curved nanographenes, where one zigzag edge is nonpassivated and the other zigzag edge is hydrogen passivated, are studied by first-principles methods. Both in finite-length nanotubes and nanographenes the gradual increase in curvature leads to a magnetic transition from antiferromagnetic coupling to ferromagnetic coupling between the two edges. With increasing curvature, the magnetic moment at a nonpassivated edge atom changes from about 1,mu(B) to about 0.6 mu(B) while the moment at a hydrogen-passivated edge atom remains about 0.2 mu(B). The transition in magnetic coupling and the change in magnetic moment are due to the different hybridization induced by curvature. The results indicate the possibility of tuning magnetization including magnetic coupling as well as magnetic moment in carbon nanotubes and graphenes by controlling curvature.