Chiral properties of bismuth ferrite (BiFeO3) inferred from resonant x-ray Bragg diffraction

TL;DR

This study reveals a new chiral phase in BiFeO3 using resonant x-ray diffraction, showing ferric ions form a cycloid structure at room temperature, which is linked to its multiferroic properties.

Contribution

It provides the first detailed characterization of a chiral ferric ion phase in BiFeO3 through azimuthal-angle scans and multipole analysis, advancing understanding of its electronic structure.

Findings

Identification of a chiral cycloid structure of ferric ions

Detection of charge-like quadrupoles at high temperature

Confirmation of chiral properties at room temperature

Abstract

A new chiral phase of ferric ions in bismuth ferrite, the only material known to support multiferroic behaviour at room temperature, is inferred from extensive sets of data gathered by resonant x-ray Bragg diffraction. Values of all ferric multipoles participating in a minimal model of Fe electronic structure are deduced from azimuthal-angle scans. Extensive sets of azimuthal-angle data, gathered by resonant x-ray Bragg diffraction, yield values of all ferric multipoles participating in a minimal model of Fe electronic structure. 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 700 K 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.