Quadrupole Spin–Lattice Relaxation of 69Ga and 71Ga in a GaAs Semi-insulator Crystal

Abstract

NMR studies of spin–lattice relaxation were carried out for two gallium isotopes, ⁶⁹Ga and ⁷¹Ga, for an undoped semi-insulator GaAs crystal under the additional continuous magnetic saturation of the nuclear spin systems at the Larmor frequencies. The magnetization recovery after inversion was observed within the temperature range from 80 to 300 K using a Bruker Avance 400 pulse spectrometer. Two main contributions to relaxation due to the hyperfine coupling with the electron centers accompanied by spin diffusion and due to the spin–phonon interaction in the regular crystal lattice were separated by suppressing the first one. Both contributions to relaxation were found to be of the quadrupole nature and followed the temperature dependence predicted for quadrupole relaxation owing to the modulation by thermal phonons of the electric field gradients at nuclei. The results obtained are consistent with the suggestion that the quadrupole hyperfine coupling dominates for nuclei in the neighborhood of the electron centers and the rapid spin diffusion approximation is satisfied.