NQR indications of unconventional magnetism in some bismuth-based diamagnets

Abstract

An evidence that local ordered magnetic fields from 30 to 200 G exist in diamagnets α-Bi2O3, Bi3O4Br, Bi4Ge3O12, Bi2Al4O9 which comprise neither d- nor f-elements was earlier given by the zerofield and Zeeman-perturbed209Bi nuclear quadrupole resonance (NQR) spectra. With a view to find similar spectroscopic effects in other compounds, we examined the209Bi NQR Zeeman-perturbed spectra of the Bi3B5O12 oriented single crystal as well as the zero-field spin echo envelopes in Bi3B5O12 and Bi2Ge3O9. Distinctive modulations were displayed by the zero-field209Bi spin echo envelopes in Bi2Ge3O9 powder. The modeling of the spin echo envelopes within the density matrix formalism explained the observed effect by the presence of local ordered magnetic field of the order of 65 G at the Bi atoms. The zero-field modulations of the209Bi spin echo envelopes were also observed in Bi3B5O12 indicating the presence of the internal source of line splitting. This finding and considerable deviation of the resonance intensity ratios from that in a pure NQR, found in the zero-field209Bi spectrum of the single crystal, were understood as indirect evidences that a local ordered magnetic field exists also in Bi3B5O12. The zero-field209Bi spin echo envelopes assigned to the lines split by the local magnetic fields in α-Bi2O3 and Bi4Ge3O12 were observed to display modulations on the appropriate curves.