Multiple magnetic singlet-singlet excitations in intermetallic PrNiSn

Abstract

Inelastic neutron-scattering experiments have been carried out on a polycrystalline sample of PrNiSn, and seven of the eight excited crystal-field singlets of the Pr ions were detected. The system stays paramagnetic, at least down to $0.9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the three principal susceptibility components have been measured on a PrNiSn single crystal between room temperature and $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The crystal-field excitations of the single crystal at low temperatures have been studied by triple-axis neutron spectroscopy. Dispersive effects are observed for three different levels of singlet-singlet excitations. The results are analyzed in terms of a mean-field/random phase approximation model, and it is concluded that the exchange interaction is highly anisotropic and of long range. The critical ratio between the maximum of the exchange interaction and that required for inducing a magnetic ordering of the singlet ground-state system is derived to be 0.48, leading to a predicted ordering temperature of $6\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ for the combined electron-nuclear magnetic system.