Nuclear Resonance of Aluminum in Synthetic Ruby

The linewidth, line shape, and spin-lattice relaxation time T₁ have been measured as a function of temperature in single crystals of (Al²⁷)₂{O}₃$ having nominal ${Cr}₂O₃ concentrations of 0% and 0.01, 0.1, 1.5, and 4% by weight. Of the two important contributions to the linewidth, the nuclear spin-spin interaction is 7 gauss and temperature-independent. The contribution from the paramagnetic ions increased from zero at 300^∘{}K to as much as 42 gauss, depending upon concentration, temperature, and static magnetic field. An anomalous structure in the aluminum resonance was evident in both the steady-state and pulsed nuclear induction data. The {} to -{} transition has a splitting of 2.84 gauss with a 3cos²θ-1 dependence on the angle between the c axis and H₀. The splitting is independent of the observation frequency and chromium ion concentration. T₁ was observed to vary from 150 sec to 1.5 msec as a function of ion concentration and temperature, and to vary in a manner not correctly given by existing theory. Many of the samples were observed to have a nonunique T₁.