NMR and the Conduction Electron Polarization in Rare-Earth Metals

The magnitude and sign of the conduction electron polarization in rare earth intermetallic compounds has been determined with the use of NMR techniques. Large, temperature-dependent Knight shifts of the ${\mathrm{Al}}^{27}$ NMR were found in $X{\mathrm{A1}}_2$ ($\mathrm{X\hspace{0.17em}\equiv \hspace{0.17em}}\mathrm{rare-earth\hspace{0.17em}ion}$ ). These observations may be explained by assuming that anegative exchange interaction of ∼0.1 ev exists between the localized $f$ electrons of the rare-earth ion and the conduction electrons.