Demagnetization of Rare Earth Ions in Metals Due to Valence Fluctuations

Magnetic‐nonmagnetic transtions of rare earth ions in metals are reviewed for both dilute and concentrated systems. Whereas magnetic behavior of a rare earth ion is associated with integral occupation of the 4f electron shell, nonmagnetic behavior is linked with nonintegral occupation. Integral occupation (valence) implies a single 4f configuration with infinite lifetime, while nonintegral occupation is a consequence of temporal valence fluctuations between two adjacent configurations. These temporal fluctuations result in nonmagnetic behavior below a characteristic temperature ${\mathrm{T}}_{\mathrm{f}}\mathrm{\hspace{0.17em}\sim \hspace{0.17em}}{\mathrm{h/k}}_{\mathrm{B}}\mathrm{\hspace{0.17em}\tau }$ because of the finite lifetime τ of the Zeeman levels.