Spin-Lattice Relaxation in Cesium Chrome Alum

The spin-lattice relaxation times of three lines of the EPR spectrum at 9.6 kMc/sec of the ${\mathrm{Cr}}^{3+}$ ion in cesium chrome alum have been measured as a function of temperature between 1.6 and 4.2°K and dilution between 0 and 36 (ratio of nonmagnetic to magnetic ions) by the steady-state saturation method. The three lines were those at the lowest field, the second lowest field, and the highest field. The rates of relaxation increase with dilution for the low-field lines, and decrease with dilution for the high-field line. The dilution dependence for the high-field line can be qualitatively explained by cross relaxation, but the dilution dependences for the low-field lines elude explanation. The relaxation rate of each resonance line shows at least two temperature dependences at each dilution. They are interpreted as arising from a combination of cross relaxation and direct processes between 1.6 and 3.0°K, and indirect processes between 3.0 and 4.2°K.