209Bi NQR studies of low-temperature spin-lattice relaxation in Bi4Ge3O12 single crystal

Unusual influence of weak external magnetic fields on quadrupole spin-spin relaxation was earlier found for Bi4Ge3O12 which exhibited, like some other compounds of composition Ba(k)Bi(1)A(m)O(n) (A = Al, B, Ge, Br, Cl), a dramatic increase in the Bi-209 NQR line intensities upon switching the magnetic field. The measuring of the nuclear quadrupole interaction parameters gave an evidence for the presence in the compound of local magnetic fields of the order of 20-30 G. The existence of several low-lying crystal field levels for the p-electrons can be admitted in Bi4Ge3O12 which contributes to the anomalies in the Bi-209 NQR spectra of this crystal. The present work was carried out to identify the contribution of such paramagnetic centers to the nuclear spin-lattice relaxation. This contribution resulted in the low-temperature minimum on the curve of the nuclear spin-lattice relaxation rate T-1(-1) vs. temperature, measured for the transition Delta m = 3/2 - 5/2 in the Bi-209 NQR spectrum of the Bi4Ge3O12 single crystal. (C) 2008 Elsevier Ltd. All rights reserved.