Electron spin resonance of ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Gd}}^{3+}$ in $d$-band intermetallic compounds

We report on the ESR of the rare-earth ions ${\mathrm{Nd}}^{3+}$, ${\mathrm{Gd}}^{3+}$, ${\mathrm{Er}}^{3+}$, and ${\mathrm{Yb}}^{3+}$ on powdered samples of various intermetallic compounds of $A{B}_2$ cubic structure where $B$ is a transition-metal ion belonging to the group VIII of the Periodic Table, and $A$ is a nonmagnetic ion (La, Ce, Y). The resonance of the ${\mathrm{Nd}}^{3+}$ in these compounds originates within a ${\Gamma }_6$ crystal-field ground level and exhibits resolved hyperfine satellites for the ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$ and ${}_{}{}^{145}{}_{}{}^{}\mathrm{Nd}$ isotopes. The ${\mathrm{Gd}}^{3+}$ spectra show a single isotropic line. Using our data for ${\mathrm{Gd}}^{3+}$ and ${\mathrm{Nd}}^{3+}$ together with results previously published for the $A{B}_2$ cubic compounds, we were able to show a correlation between the observed $g$ shifts and the position of the $B$ ion in the Periodic Table. This variation is explained qualitatively using a simple multiband model, as well as band-structure arguments. The hyperfine constants for the ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$ and ${}_{}{}^{145}{}_{}{}^{}\mathrm{Nd}$ isotopes were found smaller in magnitude with respect to the values in insulators; this effect is attributed to $s$-electron self-polarization due to the Nd localized-moment—s-electron exchange coupling. The ESR linewidths of La${\mathrm{Ir}}_2$: Nd and La${\mathrm{Rh}}_2$: Nd exhibit an exponential thermal dependence at high temperatures which is attributed to the presence of a ${\Gamma }_8$ excited level at $\Delta =90\mathrm{}\pm 20$ K.