The authors have performed ab initio calculations for the NMR relaxation rate in doped fullerenes and find that the spin-dipolar relaxation mechanism dominates the orbital and Fermi-contact mechanisms. The reason is that the states at the Fermi level are pp pi -like so that the carbon orbitals have almost exclusively radial p character. With the values 7.2 and 8.1 states/(eV spin molecule) for the bare densities of states at the Fermi level for, respectively, K3C60 and Rb3C60, plus the ab initio value 1.7 eV spin C atom for the effective Stoner exchange parameter, good agreement is obtained with the experimental relaxation rates.
 

Physical Review B, 47 12373-6, 1993.