Crystalline Electric Field Levels in Diluted Rare Earth Aluminum Cubic Laves Phases

The crystalline electric field levels of intermetallic Laves phase compounds of type ${\mathrm{R}}_{\mathrm{x}}{\mathrm{Y}}_{\text{1−}\mathrm{x}}{\mathrm{Al}}_2$ ($\mathrm{R}\mathrm{\hspace{0.17em}=\hspace{0.17em}}\mathrm{Pr}\mathrm{,\hspace{0.17em}}\mathrm{Er}\mathrm{,\hspace{0.17em}}\mathrm{Tm}$ ) have been determined by neutron spectroscopy. The polycrystalline samples have been diluted with yttrium in order to reduce magnetic interactions between the rare earth ions and thereby reducing the widths of the crystal field transition lines. However, other relaxation mechanisms and the small crystal field splittings made it impossible to separate the crystal field transition peaks completely. The intensity arising from crystal field transitions has been identified by its temperature dependence as well as by comparison with corresponding “non‐magnetic” ${\mathrm{YAl}}_2$ spectra. A least squares fitting procedure has been applied to the experimental data in order to obtain the best possible crystal field parameters. At temperatures $\mathrm{T}\text{\hspace{0.17em}>\hspace{0.17em}50\hspace{0.17em}}\mathrm{K}$ and momentum transfers $\mathrm{Q}{\text{\hspace{0.17em}>\hspace{0.17em}1\hspace{0.17em}Å}}^{\text{−1}}$ two‐phonon processes have to be taken into account in analyzing the measured energy spectra. The resulting crystal field level schemes agree qualitatively with estimates based on a nearest neighbour point charge model and quantitatively with measured susceptibility data.