Three-Spin Cross Relaxation inCr3+:K3Co(CN)6

An experiment designed to study the three-spin cross relaxation (CR) rate without interference from much faster two-spin CR processes is described. The study was performed on the electron spin system ${\mathrm{Cr}}^{3+}$ in ${\mathrm{K}}_3$Co${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_6$ and the CR rate was determined for a range of concentrations 0.036-1.030% and an energy imbalance range of ±680 MHz from the harmonic point. Comparison with Bloembergen's "hybrid" method (in the present application by an exact computation of the second moments of the shape functions) shows good agreement for concentrations in the range 0.036-0.384%. For higher concentrations, this theory does not explain the data. The experimental results are also in disagreement with a theory of Grant's, which gave a good account of several previous two-spin CR experiments.