Paramagnetic Relaxation of Some Rare-Earth Ions in Diamagnetic Crystals

The pulsed-saturation method at 8.9 kMc/sec was used to measure the spin-lattice relaxation rate T₁^-1 for Eu²⁺, Ho²⁺, and Tm²⁺ in CaF₂, for Yb³⁺ in yttrium gallium garnet, yttrium aluminum garnet, and lutetium gallium garnet; for Nd³⁺ in yttrium gallium garnet and yttrium aluminum garnet; and for Sm³⁺ in lanthanum ethyl sulphate at low temperatures. The experimental data in most cases are in satisfactory agreement with the theoretical predictions based on the combined Van Vleck-Orbach theory. Besides the expected conventional processes, a process T₁^-1∝T⁵ was observed for Eu²⁺ in CaF₂ in the temperature range 15^∘{}K30^∘{}K. Furthermore, a pronounced anisotropy in T₁ (a factor {~}6) for Sm³⁺ in lanthanum ethyl sulphate was found both experimentally and theoretically.