Dominance of the spin-dipolar NMR relaxation mechanism in fullerene superconductors

We 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{π}-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, K₃{C}₆₀$ and ${Rb}₃C₆₀, 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.