Quantum tunneling of magnetization in lanthanide single-molecule   magnets, bis(phthalocyaninato)terbium and bis(phthalocyaninato)-dysprosium   anions
  Magnetization versus field measurements were performed on single crystals of [(Pc)2TbIII0.02YIII0.98]^TBA+ and [(Pc)2DyIII0.02YIII0.98]^TBA+ (Pc: phthalocyaninato, TBA: tetrabutylammonium) at 0.04 K. The [(Pc)2TbIII] complex, the first lanthanide single-molecule magnet, exhibited clear staircase-like structures, which are assigned to resonant quantum tunneling between entangled states of the electron and nuclear spin systems. 
N. Ishikawa, M. Sugita, and W. Wernsdorfer