Angel Rodriguez-Fernandez, Stephen W. Lovesey, Steve P. Collins, Gareth Nisbet, Jesus A. Blanco
Paramagnetic (700 K) and magnetic ordered (300 K) phases of a single crystal of bismuth ferrite (BiFeO3) have been studied with Bragg diffraction of x-rays tuned near to the iron K-edge (7.1135 keV). Intensity at a reflection (0,0,9)H forbidden in the nominal space-group, R3c, recorded as a function of the rotation of the crystal about the Bragg wavevector, is consistent with a chiral structure formed by a circular cycloid propagating along (1,1,0)H. Templeton and Templeton (T&T) scattering at 700 K is attributed in part to charge-like quadrupoles absent in a standard stick-model of a cycloid, in which a material vector generates all electronic states of the resonant ion. Extensive sets of azimuthal-angle data are used to infer values of three atomic multipoles in a satisfactory minimal model of Fe electronic structure, with a quadrupole (E1-E1 event) and a hexadecapole (E2-E2 event) contributing T&T scattering, plus a magnetic dipole (E1-E1).
View original:
http://arxiv.org/abs/1305.0484
No comments:
Post a Comment