Crystal fields at light rare-earth ions in Y and Lu

Crystal-field parameters have been deduced for the light rare-earth solutes Ce, Pr, and Nd in Y or Lu hosts from measurements of the paramagnetic susceptibilities. In the analysis all multiplets in the lowest $\mathrm{LS}$ term were included. For a given host, crystal-field parameters divided by Stevens factors $\frac{B_{\mathrm{lm}}}{{\alpha }_l}$, are of approximately the same magnitude for all the solutes Pr, Nd, Tb, Dy, Ho, Er, and Tm and do not scale with $〈r^l〉$. The values deduced for Ce do not fit in with this simple picture. The higher-order parameters $B_{40}$, $B_{60}$, and $B_{66}$ are, within the errors in their determination, identical in Y and Lu hosts, indicating that these values for a specific rare-earth solute in Y and Lu may give a reliable estimate for the corresponding sites in rare-earth metal. This is confirmed for Pr, for which these values and the value of $B_{20}$ deduced from paramagnetic-susceptibility measurements on the pure metal, correctly explain the transition observed by neutron spectroscopy and the level crossing observed in a high-field experiment. A weighted average of $B_{20}$ for cubic and hexagonal sites in Nd and Sm was obtained from the paramagnetic susceptibilities of these metals at high temperatures.