Observation of quantum coherence in mesoscopic molecular magnets

By applying a transverse magnetic field B-perpendicular to of sufficient st rength to the uniaxial molecular magnets Fe-8 and Mn-12, the tunneling spli tting Delta (t) of their S = +/-10 magnetic ground states can be made large compared to perturbations such as hyperfine and dipolar interactions. We p resent evidence for such a Delta (t) from magnetic specific heat data below 1 K that is consistent with coherent quantum mechanical tunneling in a "me soscopic" system under such conditions.