Quantum tunneling and magnetic relaxation in Mn 12 chloropropionate

We have synthesized the single-molecule magnet Mn 1 2 chloropropionate and performed magnetization measurements in an applied field parallel to the easy axis of magnetization of the crystal. We found the spin S = 10 ground state and observed distinct steps in the hysteresis loops, typical of quantum tunneling of magnetization. The effective barrier height has been determined from the analyses of magnetization curves M(T) and M(H), and also from the magnetic relaxation measurements. Magnetic relaxation follows the stretched exponential law above 2 K. Compared to Mn 1 2 acetate, the relaxation rate is enhanced significantly at resonance fields, while it is more or less the same at off-resonance fields. We ascribe this observation to the transverse anisotropy in Mn 1 2 chloropropionate.