QUANTUM TUNNELING OF MAGNETIZATION IN MN(12)BZ CLUSTERS: EVIDENCES OF SPIN PARITY EFFECT

We present a comparison of the field dependence of the relaxation times observed for Mn(12)Bz, (Bz=benzoate) spin cluster, and its derivative containing one extra electron, r-Mn(12)Bz. At low temperatures Mn(12)Bz has a total spin S=10, while for the reduced sample r-Mn(12)Bz the spin of the ground state is S=19/2. Theory predicts that half integer spin should not present quantum tunneling, the so-called spin parity effect. We show evidence from experiments that quantum tunneling is partially inhibited in the reduced species. Low temperature magnetization hysteresis loops of the reduced variety do not show well-defined steps. In addition, the ac susceptibility as a function of the field also does not show a clear resonance at the expected level crossing fields, as seen in the nonreduced sample. (C) 2000 American Institute of Physics.