Cross-relaxation in nickel doped rubies

Abstract

Measurements are reported of the spin-lattice relaxation time T 1m of the Cr3+ ion in Al2O 3 when Ni3+ and Ni2+ ions are also present in very small concentrations. Well-defined reductions in T1 m are correlated with resonant cross-relaxation between Cr 3+ and Ni3+ and between Cr3+ and Ni2+. Non-resonant cross-relaxation (NCR) processes are also studied in zero magnetic field and an exponential dependence on temperature is observed. A detailed analysis enables us to suppose that those Ni3+ ions for which the two lower doublets are split by ~ 6 cm -1 dominate the NCR process. Also reported is the observation of a reduction in T1m when a fast relaxing Ni3+ or Ni2+ ion is resonant with à Cr3+ transition other than that being monitored. Cross-relaxation processes involving three spins — one Cr3+ and two Ni or vice versa — are also discussed. In samples with less than ~ 0.03 at. % Cr, cross-relaxation within the Cr3+ system itself is only important when two or three spins are involved, one of which involves a transition at the monitored frequency. A three-spin Cr3+ process is observed in which all transition frequencies are different