Studies of the Ni3+:Al2O3system by thermal conductivity measurements

A detailed investigation of the phonon-spin interaction in the system Ni 3+ :Al 2 O 3 has been carried out by low-temperature thermal conductivity measurements on single crystals (0.05 to 100K). Using the theoretical model of Abou-Ghantous et al. (1974) to describe the vibronic energy levels, a complete quantitative analysis of the data has been achieved with two resonant phonon scatterings at 0.47 cm -1 and 55 cm -1 , taking into account the residual strains which play a major role in the low-frequency resonance. From the measurements with applied uniaxial stress the ion-lattice coupling constant has been determined as V E b=60000+or-9000 cm -1 . It has been also possible to estimate the magnitude of the E-type random strains ( approximately=10 -5 ) and the concentration of the Ni 3+ ions in the crystals (0.2 to 5 ppm weight).