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

Abstract The results of the 209 Bi NQR experiments carried out on α-Bi 2 O 3 , Bi 3 O 4 Br, Bi 2 M 4 O 9 ( M =Al, Ga), Bi 2 Ge 3 O 9 , and Bi 4 Ge 3 O 12 showed that these compounds are not diamagnets in the conventional sense. The Zeeman perturbed zero-field 209 Bi NQR spectra gave an indication that local ordered magnetic fields 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 209 Bi NQR experiments on the Bi 4 Ge 3 O 12 single crystal in external magnetic fields below 500 Oe, applied at various orientations with respect to the crystal axes. The spectral patterns of dramatically increased intensity and multiplicity, caused by the unknown magnetism of the compound, were observed in applied fields and modeled. Based on the results of the modeling, the conclusions were made that at least four magnetically non-equivalent Bi sites characterized by antiferromagnetically ordered local fields of the order of 30 G are present in the Bi 4 Ge 3 O 12 crystal; the intensity increase was interpreted to arise from the change in orientation of the electric field gradient axes at the Bi site upon applying an external magnetic field.