Local ordered magnetic fields in bismuth dielectrics, Bi-209 NQR in Bi4Ge3O12 single crystal

The results of the Bi-209 NQR experiments carried out on alpha -Bi2O3, Bi3O 4Br, Bi2M4O9 (M = Al, Ga), Bi2Ge3O9, and Bi4Ge3O12 showed that these compou nds are not diamagnets in the conventional sense. The Zeeman perturbed zero -field Bi-209 NQR spectra gave an indication that local ordered magnetic fi elds of the order of 30-200 G exist in these substances comprising neither transition nor rare earth elements. Further aspects of this principally new phenomenon of yet unknown nature were studied by the Bi-209 NQR experiment s on the Bi4Ge3O12 single crystal in external magnetic fields below 500 Oe, applied at various orientations with respect to the crystal axes. The spec tral patterns of dramatically increased intensity and multiplicity, caused by the unknown magnetism of the compound, were observed in applied fields a nd modeled. Based on the results of the modeling, the conclusions were made that at least four magnetically non-equivalent Bi sites characterized by a ntiferromagnetically ordered local fields of the order of 30 G are present in the Bi4Ge3O12 crystal; the intensity increase was interpreted to arise f rom the change in orientation of the electric field gradient axes at the Bi site upon applying an external magnetic field. (C) 2001 Elsevier Science B .V. All rights reserved.