Neutron Crystal-Field Spectroscopy in Rare-Earth Metallic Compounds

Abstract

The technique of inelastic neutron scattering has been applied to the problem of crystal fields in rare-earth metallic compounds. It is shown that in compounds where the Stark energies are somewhat greater than exchange energies, the complete energy-level diagram can be readily obtained from the inelastic neutron spectra and hence the corresponding crystal-field parameters may be deduced. In this paper we illustrate this by a series of measurements which we have performed on the praseodymium monopnictides, PrBi, PrSb, PrAs, PrP, and monochalcogenides PrTe, PrSe, PrS. It is found that the spectra can be reproduced in detail using ordinary crystal-field theory together with a simple approximation to the instrumental resolution function. In addition, all of the crystal-field levels in all seven compounds studied can be quantitatively accounted for using a nearest-neighbor point charge model with an effective charge of −2. This is in spite of marked variations in covalency, carrier concentration and, indeed, in the widths of the crystal-field transitions themselves over the series.