SPIN-LATTICE RELAXATIONS OF BE-9 AND AL-27 IN SINGLE-CRYSTALLINE ALEXANDRITE

Nuclear spin-lattice relaxations of Be-9 and Al-27 in an alexandrite ( BeAl2-xCrxO4, x=0.02) single crystal have been investigated in the tem perature range 140 K-400 K. The paramagnetic impurity effect on the re laxation is negligible for both nuclei. The relaxation of the Be-9 nuc lear spins is found single exponential in time when the whole resonanc e lines are uniformly excited. When only the central resonance line is excited for Al-27, the relaxation is well fitted with a linear combin ation of three exponential functions given by Simmons et al. [Phys. Re v. 127, 1168 (1962)]. Since the spin-lattice relaxation rate is propor tional to the square of temperature for both nuclei, the dominant rela xation mechanism in this temperature range can be inferred as the Rama n process. (C) 1997 American Institute of Physics.