Experimental Study of Relaxation Processes for Divalent Cobalt Ions

The nuclear orientation produced for stable ${\mathrm{Co}}^{59}$ nuclei of divalent cobalt ions in the $X$ site of ${\mathrm{La}}_2$ ${\mathrm{Zn}}_3$ ${\left(\mathrm{N}{\mathrm{O}}_3\right)}_{12}$·24${\mathrm{H}}_2$O by saturation of allowed and forbidden transitions between levels of the hyperfine structure in a strong magnetic field has been deduced from measurements of the intensity of allowed transitions while some other transition was saturated. These measurements give more detailed results than just the nuclear orientation; and, when combined with transient measurements, permit one to deduce the values of the many relaxation rates. The relaxation rates depend strongly on the direction of the applied magnetic field but can all be predicted rather accurately by the theory presented in the preceding paper when an appropriate and reasonable choice is made for the four constants left undetermined in that theory. The temperature dependence of the relaxation rates is of the form $\frac{1}{(aT+b{T}^9)}$ and, below 2.2°K, the direct process dominates. The most striking effects are the extreme importance of the hyperfine relaxation effects, and a perfect Overhauser effect, producing nuclear alignment opposite in sign from that usually anticipated.