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, T1, of 69Ga and 71Ga nuclei in a β-Ga2O3:Cr3+ single crystal were obtained using FT NMR spectrometry. Four sets of NMR spectra for 69Ga (I = 3/2) and 71Ga (I = 3/2) were obtained in the crystallographic planes. The 69Ga and 71Ga nuclei each had two chemically inequivalent GaI and GaII centers. Each of the 69Ga and 71Ga isotopes yielded two different central NMR resonance lines originating from GaI and GaII sites. The nuclear quadrupole coupling constants and asymmetry parameters of 69GaI, 69GaII, 71GaI, and 71GaII centers in a β-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 69Ga and 71Ga relaxation rates were consistent with Raman processes, as T1−1 ∝ T2. Even though the Cr3+ impurities are paramagnetic, the relaxations were dominated by electric quadrupole interactions of the nuclear spins in the temperature range investigated.