E. A. Kravchenko

209Bi NQR and Magnetic Properties of Bismuth Oxide-Based Compounds

Abstract The NQR line shapes of 209Bi in the α-Bi2O3-based mixed oxides Bi2O3 • 2M2O3 (M = Al, Ga). Bi2O3 • 3GeO2, and 2Bi2O3 • 3GeO2 are recorded in zero and weak magnetic fields (Hext < 500 Oe) and compared with the results of computer simulation. Splittings and line shape asymmetry, exhibited by the resonances, suggest that internal magnetic fields, similar to those earlier reported for α-Bi2O3 and Bi3O4Br, may exist in these compounds. In the spectra of single crystal Bi4Ge3O12, the line multiplicity in external magnetic fields is higher than simulated, which might results from domains in the crystal. In external magnetic fields a notable increase in the line intensity was observed, the effect depending on the mutual orientation of the EFG axes and the fields perturbing the nuclear spin system.

Magnetism of Bismuth(III) Oxide-Based Compounds

209Bi NQR experiments, including analysis of zero-field line shapes, Zeeman-perturbed patterns and zero-field spin-echo envelopes were made to examine magnetic splitting of resonances revealed in the spectra of Main group element compounds of general composition BakBilAmOn (A=Al, В, Ge, Br, Cl). The results were explained assuming the existence in the compounds of ordered internal magnetic fields from 5 to 250 G which notably exceed those of nuclear magnetic moments. A dramatic (8−10-fold) increase in the resonance intensities, instead of broadening and fading, was observed for such compounds upon applying weak (below 500 Oe) external magnetic fields. The effect was shown to relate to the spin dynamics, namely, to the influence of external magnetic field on the nuclear spin-spin relaxation of the compounds with anomalous magnetic properties. In α-Bi2O3, paramagnetism depending on the thermal prehistory of a sample was found using SQUID-technique; magnetoelectric effect linear in magnetic field was also observed for this oxide.