Origin of Knight-shift anomaly in intermediate-valence compounds

A strong anomaly in the expected linear relation between ${}_{}{}^{31}{}_{}{}^{}\mathrm{NMR}$ Knight shift and bulk magnetic susceptibility is observed at low temperatures for an intermediate-valence Eu-based compound, i.e., ${\mathrm{EuNi}}_2$ ${\mathrm{P}}_2$. It is shown that this anomaly is not caused by crystalline–electric-field or lattice-volume effects. Instead, it is the result of the formation of the hybridized 4f conduction-electron ground state at low temperatures.