MAGNETIC-RESONANCE OF FULLERENE SOLIDS AND THEIR COMPOUNDS

Nuclear magnetic resonance (NMR) measurements on the novel materials C60 and C70, and their compounds with the alkali metals, are reported and reviewed. A sharp change in the NMR relaxation time T1 at 263 K with a hysteresis of 1 K corresponding to an orientational phase transition was found in sublimed C60 powder. A similar abrupt change in T1(-1) at 280 K was also found in sublimed C70 powder, which is ascribed to the same kind of phase transition as found in C60, although here it is restricted to uniaxial rotation around the long ellipsoidal axis and unlike free rotation in the case of C60. At temperatures above 340 K however, three-dimensional free rotation can take place. A curious behavior of the ESR intensity was observed for the pure C60 powder. The ESR intensity strongly decreased upon exposure of air instead of the expected increase upon exposure to oxygen and light. C-13 NMR T1 measurements on the three superconducting compounds were analyzed in terms of a relation between T(c) and the density-of-states at the Fermi energy.