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 expe riments in the energy region below 85 mu eV for the octanuclear iron molecu lar 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-n eutron backscattering spectrometer, we observed two magnetic peaks at 14.5 and at 7.5 mu eV. Their position and intensity support a previous determina tion of the zero-field splitting parameters by neutron spectroscopy. The ex perimental findings are discussed in relation to very recent quantum phase interference and single-crystal electron paramagnetic resonance measurement s.