Cross Relaxation in Ruby

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Abstract
A pulsed microwave method has been used to study paramagnetic relaxation in synthetic ruby at Cr/Al concentrations from 0.02% to 0.3%, and over a wide range of fields and angles with respect to the crystal axis. The experimental frequency was 7.17 kMc/sec. At settings for which one interval between energy levels was twice as large as another, decay traces with two characteristic periods were observed. The more rapid decay was independent of temperature, and is attributed to a cross-relaxation process involving three spins. Similar behavior became apparent at all concentrations whenever two intervals approached the same value. At 0.3%, two period decay traces were observed for any arbitrary field and angle setting, indicating at this concentration, a general cross relaxation between the Zeeman levels in times of 0.3 millisecond and less.