Study of nuclear quadrupole interactions and quadrupole Raman processes of 69Ga and 71Ga in a β-Ga2O3:Cr3+ single crystal

Nuclear magnetic resonance (NMR) data and the spin-lattice relaxation times, T-1, of Ga-69 and Ga-71 nuclei in a beta-Ga2O3:Cr3+ single crystal were obtained using FT NMR spectrometry. Four sets of NMR spectra for Ga-69 (I = 3/2) and Ga-71 (I = 3/2) were obtained in the crystallographic planes. The Ga-69 and Ga-71 nuclei each had two chemically inequivalent Ga-I and Ga-II centers. Each of the Ga-69 and Ga-71 isotopes yielded two different central NMR resonance lines originating from GaI and GaII sites. The nuclear quadrupole coupling constants and asymmetry parameters of Ga-69(I), Ga-69(II), Ga-71(I), and Ga-71(II) centers in a beta-Ga2O3:Cr3+ crystal were obtained. Analysis of the EFG tensor principal axes (PAs) for Ga nuclei and the ZFS tensor PAs for the Cr3+ ion confirmed that the Cr3+ paramagnetic impurity ion substitutes for the Ga3+ ion in the oxygen octahedron. In addition, the temperature dependencies of the Ga-69 and Ga-71 relaxation rates were consistent with Raman processes, as T-1 (1) proportional to T-2. Even though the Cr3+ impurities are paramagnetic, the relaxations were dominated by electric quadrupole interactions of the nuclear spins in the temperature range investigated. (C) 2009 Elsevier Inc. All rights reserved.