Spin-lattice relaxation of the Cr³⁺ ion in ruby at 35 Gc/s

Spin-lattice relaxation time (T₁) measurements were carried out at 35 Gc/s on the ruby samples used previously by Standley and Vaughan at 9 3 Gc/s. Values of T₁ of the order of 20 msec were found at 4 2 °k. The results are compared with theoretical predictions of Donoho. Vapour-phase grown rubies show a greater angular variation of T₁ than Verneuil or fluxed-melt grown samples but magnitudes are only about one-quarter of those predicted and the observed angular variation is less than that calculated. This is in contrast with the 9 3 Gc/s results and the concentration independence observed at that frequency is now less obvious. It is shown that harmonic cross relaxation can play an important role at the higher frequencies in determining the absolute magnitudes of the measured relaxation parameter and its angular variation.