ORIENTATIONAL AND MAGNETIC-ORDERING OF BUCKYBALLS IN TDAE-C-60

Spin ordering in the low-temperature magnetic phase is directly linked to the orientational ordering of C-60 molecules in organically doped fullerene derivatives. Electron spin resonance and alternating current susceptometry measurements on tetrakis(dimethylamino)ethylene-C-60 (TDAE-C-60) (Curie temperature T-c = 16 kelvin) show a direct coupling between spin and merohedral degrees of freedom. This coupling was experimentally demonstrated by showing that ordering the spins in the magnetic phase imprints a merohedral order on the solid or, conversely, that merohedrally ordering the C-60 molecules influences the spin order at low temperature. The merohedral disorder gives rise to a distribution of pi-electron exchange interactions between spins on neighboring C-60 molecules, suggesting a microscopic origin for the observed spin-glass behavior of the magnetic state.