We present the results of high-resolution inelastic neutron scattering experiments in the energy region below $85\hspace{0.5em}\mu \mathrm{eV}$ for the octanuclear iron molecular cluster ${\mathrm{Fe}}_8,$ which are relevant to the problem of determining the zero-field splitting parameters of the $S=10\mathrm{}$ spin ground state. By using a cold-neutron backscattering spectrometer, we observed two magnetic peaks at $14.5$ and at $7.5\hspace{0.5em}\mu \mathrm{eV}.$ 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.

• Received 4 April 2000

DOI:https://doi.org/10.1103/PhysRevB.62.3022