Spin-lattice relaxation rates forNd3+,Er3+, andCe3+in LaCl3between 2.7 and 29 K

The spin-lattice relaxation rates of ${\mathrm{Nd}}^{3+}$, ${\mathrm{Er}}^{3+}$, and ${\mathrm{Ce}}^{3+}$ in La${\mathrm{Cl}}_3$ have been measured in two nonoverlapping temperature regions between 2.7 and 29 K using pulse-saturation-recovery techniques to measure $T_1$ at the lower temperatures, and linewidth broadening to measure $T_2$ at the higher temperatures. $T_2$ data from Nd exhibit dominant, isotropic Orbach relaxation mechanisms involving the first two excited states at 166.0 and 177.3 K. There is indirect evidence from the $T_1$ data that these Orbach rates are phonon limited, i.e., bottlenecked. The $T_1$ data for Nd also show a dominant Raman relaxation process between 5 and 8 K but there is a 100% angular anisotropy measured at 6 K. $T_2$ data from Er show Orbach relaxation processes involving the first two excited states at 54.55 and 92.47 K, and together with the $T_1$ data indicate that the Orbach process involving the lower energy level, is phonon limited. $T_2$ data from Ce show a completely dominant Orbach relaxation process involving an excited state at 53.3 ± 1.7 K. This is in good agreement with the optical value of 54.0 ± 4.5 K, but in sharp contrast to all previous data involving $T_1$ measurements where values of 46 K were reported. An existing model for this discrepancy predicts that it should diminish at higher temperatures where our $T_2$ measurements were made.