Quantum coherence in Fe-8 molecular nanomagnets

We report observation of coherent quantum oscillations in spin-10 Fes molec ular clusters. The powder of magnetically oriented Fe-8 crystallites was pl aced inside a resonator, in a de magnetic field perpendicular to the magnet ization axis. The field dependence of the ac-susceptibility was measured up to 5 T, at 680 MHz, down to 25 mK. Two peaks in the imaginary part of the susceptibility have been detected, whose positions coincide, without any fi tting parameters, with the predicted two peaks corresponding to the quantum splitting of the ground state in the magnetic field parallel and perpendic ular to the hard magnetization axis.