Nuclear Quadrupole Coupling and Crystal-Field Effects in the Cubic Intermetallic Compounds ErAl3, TmAl3, and YbAl3

The presence of a large nuclear quadrupole coupling of the Al nucleus, as measured with NMR, in the cubic rare-earth aluminum intermetallic compounds $\beta$-Er${\mathrm{Al}}_3$, Tm${\mathrm{Al}}_3$, and Yb${\mathrm{Al}}_3$ indicates that the net charges at the rare-earth and aluminum sites differ by as much as 3 to 4 unit charges. Data on the magnetic susceptibility and this result have been used to analyze crystal-field effects in Tm${\mathrm{Al}}_3$. The ground state appears to be a nonmagnetic doublet ${\Gamma }_3$, the next higher level being the triplet ${\Gamma }_5^{\mathrm{}\left(1\right)\mathrm{}}$ at a distance of 45°K. In addition, from the Knight shift, exchange constants between conduction electrons and $4f$ electrons have been derived to be ${\mathcal{I}}_{\mathrm{sf}}=-0.24\mathrm{}$ eV.