209Bi NQR studies of low-temperature spin–lattice relaxation in Bi 4Ge 3O 12 single crystal

Abstract

Unusual influence of weak external magnetic fields on quadrupole spin–spin relaxation was earlier found for Bi 4Ge 3O 12 which exhibited, like some other compounds of composition Ba kBi lA mO n (A=Al, B, Ge, Br, Cl), a dramatic increase in the 209Bi 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 Bi 4Ge 3O 12 which contributes to the anomalies in the 209Bi 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 Δ m = 3 / 2 − 5 / 2 in the 209Bi NQR spectrum of the Bi 4Ge 3O 12 single crystal.