High Magnetic Field Spin-Lattice Relaxation Rates in the Ground Quartet State of a Cr³⁺ Ion in Ruby

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Relaxation-rates in ⁴A₂ state of a Cr³⁺ ion in ruby have been studied by optical observation on population changes caused by application of magnetic field of rectangular pulses at 4.2 K. The direct one phonon emitting process is dominant in the field range from 47 kOe to 128 kOe. No transition occurs between the levels (Remark: Graphics omitted.) and (Remark: Graphics omitted.), where M_S is the component of spin angular momentum along the field. The two types of transitions, ΔM_S=2 and ΔM_S=1, are found to constitute the spin-lattice relaxation. The rates of these transitions are (7.66±0.15)×10⁻⁴ H² ms⁻¹, and (7.65±0.20)×10⁻⁵ H² ms⁻¹, respectively, where H is the magnetic field strength in kOe.