Study of crystalline electric fields inRD2(R=Tb,Dy,Ho,Er) using neutron inelastic scattering

Neutron energy-loss spectra of $R{\mathrm{D}}_2$ ($R=\mathrm{T}\mathrm{b},\mathrm{D}\mathrm{y},\mathrm{H}\mathrm{o},\mathrm{E}\mathrm{r}$) were taken using powder samples on a triple-axis spectrometer. Excitations, believed to be crystalline electric-field (CEF) transitions were observed for all the compounds. In Dy${\mathrm{D}}_2$, the observed transition energy is in good agreement with the CEF parameters derived from magnetic susceptibility and Mössbauer spectroscopy. The observed transitions in the spectra of Ho${\mathrm{D}}_2$ and Er${\mathrm{D}}_2$ could not be fitted, taking into account the relative intensities, to any calculated scheme of cubic symmetry. With Tb${\mathrm{D}}_2$, it was possible to fit the spectra to a calculated scheme and CEF parameters were deduced for $T>\mathrm{}{T}_N$. However, these parameters failed to yield the correct $T_N$ in the molecular-field calculations. Hence, a cubic CEF model is, in general, insufficient for describing the CEF transitions in $R{\mathrm{D}}_2$.