NQR indications of unconventional magnetism in some bismuth-based diamagnets

Abstract

Ala evidence that local ordered magnetic fields from 30 to 200 G exist in diamagnets ct-Bi203, Bi304Br, Bi4Ge3Oi2, Bi2AI409 which comp¡ neither d-nor f-elements was earlier given by the zerofield and Zeeman-perturbed 2~ nuclear quadrupole resonance (NQR) spectra. With a view to fmd similar spectroscopic effects in other compotmds, we examined the 2~ NQR Zeeman-perturbed spectra of the Bi3BsO~2 oriented single crystal as well as the zero-field spin echo envelopes in Bi3B50~2 and Bi2Ge309. Distinctive modulations were displayed by the zero-field 2~ spin echo envelopes in Bi2Ge309 powder. The modeling of the spin echo envelopes within the density matrix formalism explained the observed effect by the presente of local ordered magnetic field of the order of 65 G at the Bi atoms. The zerofield modulations of the Z~ spin echo envelopes were also observed in Bi3B5OI2 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-field 2~ spectrum of the single crystal, were understood as indirect evidences that a local ordered magnetic field exists also in Bi3BsO12. The zero-field 2~ spin echo envelopes assigned to the lines split by the local magnetic fields in a-Bi203 and Bi4Ge3Ot2 were observed to display modulations on the appropriate curves.

Local Magnetic Fields in Some Bismuth-Based Diamagnets

“…2 in [5]). No line splitting was found in the zero-field 209 Bi NQR spectrum of Bi 3 B 5 O 12 (orthorhombic, Pnma), although the resonance intensity ratio measured in the single crystal for the v 2 Bi(1) and v 2 Bi(2) transitions (Table I) deviated considerably from that in a pure NQR spectrum [6]. In addition, the SEE for the v 2 Bi(1) line was modulated in zero field revealing the presence of the internal source of line splitting.…”

“…In addition, the SEE for the v 2 Bi(1) line was modulated in zero field revealing the presence of the internal source of line splitting. Both findings were understood as an indication that a weak H loc exists in Bi 3 B 5 O 12 [6].…”

“…The effect was explained, based on the results of modeling the SEE within the density matrix formalism, by the presence of H loc of the order of 65 G at the Bi sites. Evidence was also obtained for the presence of H loc in Bi 3 B 5 O 12 [6].…”

“…The procedure of modeling the 209 Bi line splittings was described in [3Y5]. The main steps of modeling the SEE based on the matrix density formalism were described in [6].…”

“…An examination of powdered Bi 2 Ge 3 O 9 revealed distinctive zero-field modulations displayed by the 209 Bi spinYecho envelopes (SEE) [6]. The effect was explained, based on the results of modeling the SEE within the density matrix formalism, by the presence of H loc of the order of 65 G at the Bi sites.…”