MAGNETIC-SUSCEPTIBILITY OF MOLECULAR CARBON - NANOTUBES AND FULLERITE

Elemental carbon can be synthesized in a variety of geometrical forms, from three-dimensional extended structures (diamond) to finite molecu les (C-60 fullerite). Results are presented here on the magnetic susce ptibility of the least well-understood members of this family, nanotub es and C-60 fullerite. (i) Nanotubes represent the cylindrical form of carbon, intermediate between graphite and fullerite. They are found t o have significantly larger orientation-averaged susceptibility, on a per carbon basis,than any other form of elemental carbon. This suscept ibility implies an average band structure among nanotubes similar to t hat of graphite. (ii) High-resolution magnetic susceptibility data on C-60 fullerite near the molecular orientational-ordering transition at 259 K show a sharp jump corresponding to 2.5 centimeter-gram-second p arts per million per mole of C-60. This jump directly demonstrates the effect of an intermolecular cooperative transition on an intramolecul ar electronic property, where the susceptibility jump may be ascribed to a change in the shape of the molecule due to lattice forces.