Relaxation Time Measurements in Ruby by a dc Magnetization Technique

Relaxation-time measurements by observation of the recovery of the z component of the dc magnetization have been carried out in ruby. Harmonic cross-relaxation processes, involving two, four, and five spins, have been identified. The cross-relaxation time for the five-spin process is found to be proportional to f^-2.6, where f=Cr:Al atom ratio. The spin-lattice relaxation time is proportional to f^-1 for small f, but decreases faster at higher concentrations. The temperature dependence as T^-1 or T^-2 can be explained by a model of cross relaxation between single ions and exchange coupled pairs. The magnetic field dependence is small.