A NEW MECHANISM FOR FERROMAGNETISM IN C-60-TDAE

Based on the topology of C-60 and the resulting non-disjoint nature of the lowest unoccupied molecular orbitals, Ne propose a new model for ferromagnetic exchange in C-60-TDAE. Within the Hubbard model, we find that the ferromagnetic exchange integral is stabilized to first order in the inter-ball transfer integral, while the antiferromagnetic coup ling is stabilized only to second order. This difference is adequate t o counter the larger phase space available for stabilizing the antifer romagnetic state. Thus, the ground state is found to be ferromagnetic for reasonable inter-ball transfer integrals.