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

Abstract

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 \ifmmode\pm\else\textpm\fi{} 1.7 K. This is in good agreement with the optical value of 54.0 \ifmmode\pm\else\textpm\fi{} 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.