Quadrupole spin-echo envelopes for $\mathrm{Bi_4Ge_3O_{12}}$ single crystals doped with atoms of transition and rare earth elements

Influence of weak (below 50 Oe) constant magnetic field on quadrupole spin-echo envelope was studied for non-doped single crystal $\mathrm{Bi_4Ge_3O_{12}}$, in which local magnetic fields of the order of 20–30 G were earlier found, as well as for single crystals $\mathrm{Bi_4Ge_3O_{12}}$ doped with atoms of transition and rare earth elements. In all the cases, the spin-echo envelopes were strongly influenced. A considerable increase in the nuclear spin-spin relaxation time $T_2$ was observed for the non-doped sample upon switching weak external magnetic fields. For the doped samples, the spin-echo envelope decay became much slower already in zero field. The external magnetic fields exhibited markedly weaker influence on the spin-echo envelope for the doped samples.