Chiral Properties of BiFeO3 Inferred from Resonant X-ray Bragg Diffraction.

A new chiral phase of ferric ions in bismuth ferrite (BiFeO₃), the only material known to support multiferroic behaviour at room temperature, is inferred from extensive sets of data gathered by resonant x-ray diffraction. Values of all ferric multipoles participating in a minimal model of Fe electronic structure are deduced from azimuthal-angle scans. Paramagnetic (700 K) and magnetically ordered (300 K) phases of a single crystal of BiFeO₃ have been studied with x-rays tuned near to the iron K-edge (7.1135 keV). At both temperatures, intensities at a Bragg spot forbidden in the nominal space-group, R3c, are consistent with a chiral motif of ferric ions in a circular cycloid propagating along (1, 1, 0)_H. Templeton and Templeton scattering at 700K is attributed in part to charge-like quadrupoles in a cycloid. The contribution is not present in a standard, simplified model of electronic states of the resonant ion with trivial cylindrical symmetry. [ABSTRACT FROM AUTHOR]