High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb-2@C79N with a Single-Electron Terbium-Terbium Bond

The azafullerene Tb-2@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 Tb-2@C79N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time tau(QTM)=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.