Magnetic Properties of Novel Carbon Allotropes

This chapter elaborates the magnetic properties of novel carbon allotropes. The polyhedral molecules of fullerene, C₆₀, undergo cross-linking reactions when annealed at pressures to form a variety of crystalline polymers with layered structures. These polymerized fullerenes (poly-Cm) demonstrate ferromagnetic behavior only when prepared in a relatively narrow range of synthesis conditions. This indicates that the process of formation of a ferromagnetic phase may be related to the occurrence of the defects due to cage opening. It is also feasible that the weak bonds between polyhedra are readily broken, and can act as the spin centers. The possibility of magnetic centers arising in defective polyhedral cages was examined in a study that modeled poly-C₆₀ using a combination of reactive force field molecular dynamics and hybrid-exchange density functional theory. The calculations showed that it was particularly favorable for hydrogen to bind at one of the three types of spin centre in this particular defect, and that the perturbation introduced by hydrogen quenched the antiferro coupling pathway selectively, leading to ferromagnetism with moment.