Ferromagnetism of double-walled carbon nanotubes

The pure double-walled carbon nanotubes (DWNTs) and two endohedral DWNTs (DWNTs with materials filled inside) are produced. The filling materials are CoI(2) and KI, respectively. The ferromagnetism (FM) is observed in pure DWNTs. The content of residual catalyst Fe is too small to be responsible for the observed FM. On the other hand, after filling KI or CoI(2) into the tubes, over 87% of FM is suppressed. This suggests that the origin of FM in nanotubes is mainly from the hydrogen chemisorptions induced in the process of acid purification. With the knowledge of FM origin, it is then possible to enhance FM of carbon nanotubes or graphene for applications relying on magnetism. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3453867]