Separation of quadrupole and magnetic mechanisms of 209Bi nuclear spin-lattice relaxation in Bi4Ge3O12

Bi4Ge3O12 belongs to the class of complex Bi-oxides (alpha-Bi2O3, Bi3O4Br) which exhibits unusual magnetic properties. Local magnetic fields of about 30 G were revealed in the Bi4Ge3O12 single crystal by Bi-209 NQR experiments. In the present paper the nuclear spin-lattice relaxation was studied in the Bi4Ge3O12 single crystal by Bi-209 NQR spin-echo technique. The experimental relaxation curves were described by the single effective spin-lattice relaxation time T-1. The temperature dependence of 1/T-1 was close to T-n law with n = 2.4-2.7. The nuclear spin-lattice relaxation in the multi-level system was theoretically calculated for the case of single-axial crystalline electric field. Both quadrupole and magnetic mechanisms of relaxation were taken into account. We conclude that the magnetic mechanism contributes noticeably to the spin-lattice relaxation in Bi4Ge3O12 at T less than or equal to 50 K.