High blocking temperature of magnetization and giant coercivity in the azafullerene Tb2@C79N with a single-electron Tb-Tb bond.

The azafullerene Tb2@C79N is found to be a single molecule magnet with a high 100-s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy-axis single-ion magnetic anisotropy are strongly coupled by the unpaired spin of the single-electron Tb-Tb bond. Relaxation of magnetization in Tb2@C79N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τQTM = 16462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped.