  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.
