Inelastic neutron scattering below 85 mu eV and zero-field splitting parameters in the Fe-8 magnetic cluster

We present the results of high-resolution inelastic neutron scattering experiments in the energy region below 85 mu eV for the octanuclear iron molecular cluster Fes, which are relevant to the problem of determining the zero-field splitting parameters of the S=10 spin ground state. By using a cold-neutron backscattering spectrometer, we observed two magnetic peaks at 14.5 and at 7.5 mu eV. Their position and intensity support a previous determination of the zero-field splitting parameters by neutron spectroscopy. The experimental findings are discussed in relation to very recent quantum phase interference and single-crystal electron paramagnetic resonance measurements.