Indirect evidence for exchange modification of the conduction bands inRAl2compounds

The self-polarization contribution to the total hyperfine field at a rare-earth nucleus should be directly correlated with a variation in the hyperfine splitting parameter as seen by the $4f$ electron of the rare-earth ion. Comparison of data on the hyperfine field in ordered Er${\mathrm{Al}}_2$ and Dy${\mathrm{Al}}_2$ with paramagnetic resonance results for Er and Dy in Sc${\mathrm{Al}}_2$, Lu${\mathrm{Al}}_2$, and Yb${\mathrm{Al}}_2$ suggests that the self-polarization effect is large in the ferromagnetic phase but negligible in the paramagnetic phase. Analysis of available data on some Pr and Tm compounds also suggests self-polarization effects to be negligible in the paramagnetic phase. We conclude that modification of the conduction-electron band structure due to exchange splitting effects may play an important role in the rare-earth—${\mathrm{Al}}_2$ compounds.