Electronic properties and phase transitions of RbC60 and CsC60: Investigation by NMR spectroscopy
Abstract
We report the results of 133Cs, 87Rb, and 13C NMR measurements on the alkali-metal fullerides CsC60 and RbC60. Measurements of NMR spectra and spin-lattice relaxation rates provide clear evidence for phase transitions near 300 K in both compounds, with substantial changes in their electronic properties at the phase transitions. The high-temperature phases are paramagnets, with an exchange coupling of roughly 2 cm-1 between electron spins that are localized primarily on C-60 ions. The 133Cs and 87Rb NMR frequency shifts and relaxation rates are determined by Fermi contact hyperfine couplings to the electron spins. The 13C relaxation rates are determined by dipolar hyperfine couplings. The electron-spin susceptibility is greatly reduced in the low-temperature phases
- Publication:
-
Physical Review B
- Pub Date:
- September 1993
- DOI:
- 10.1103/PhysRevB.48.9097
- Bibcode:
- 1993PhRvB..48.9097T
- Keywords:
-
- 61.46.+w;
- 74.70.Wz;
- 76.60.-k;
- Fullerenes and related materials;
- Nuclear magnetic resonance and relaxation