Low-temperature Theory of Proton NMR in the Molecular Antiferromagnetic Ring Fe10

The proton nuclear spin-lattice relaxation rate 1/T1 in the mol. "ferric wheel" Fe10(OCH3)20(C2H2O2Cl)10 (Fe10) is calcd. in the framework of the linear response theory, starting from the unperturbed eigenvalues and eigenstates of the magnetic ring. The dipole-dipole superhyperfine interaction between the proton nuclear spins and the electronic spins of the magnetic ions is shown to induce transitions between states |S, M> which differ by 1 both in the quantum no. S (the total spin of the ring) and in M (the projection of the total spin along the quantization axis). The theory predicts that level crossing between the states |S + 1, -(S + 1)> and |S, -S> induced by an applied magnetic field should be accompanied by a strong enhancement of T1-1, in good agreement with recent low-temp. NMR exptl. data on Fe10.