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Instruments / Technical Area	Publication Details	Published
I16-Materials and Magnetism	A new chiral phase of BiFeO3 evidenced from resonant x-ray Bragg diffraction A. Rodriguez-Fernandez , S. W. Lovesey , S. P. Collins , G. Nisbet , J. A. Blanco Journal Of Physics: Conference Series 519, 191 REXS 2013 - Workshop on Resonant Elastic X-ray Scattering in Condensed Matter DOI: 10.1088/1742-6596/519/1/012012 Diamond Proposal Number(s): [7720] Open Access Show Abstract ▼ Abstract: Results that support a new chiral phase in the only multiferroic material known above room temperature have been obtained by a resonant x-ray Bragg diffraction experiment, with the incoming x-ray beam tuned near the Fe K-edge (7.1135 keV), performed in its ferroelectric phase. The R3c forbidden reflection (0,0,9)H was studied as a function of the rotation of the crystal about the Bragg wavector in both phases, paramagnetic (700 K) and antiferromagnetic (300 K). The data gathered 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 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 the iron electronic structure, with a quadrupole (E1-E1 event) and a hexadecapole (E2-E2 event) contributing T&T scattering, plus a magnetic dipole (E1-E1).	May 2014
I16-Materials and Magnetism	Chiral properties of BiFeO3 inferred from resonant X-ray Bragg diffraction Angel Rodriguez-Fernandez , Stephen Lovesey , Stephen P. Collins , Gareth Nisbet , Jesus A. Blanco Journal Of The Physical Society Of Japan 83 (1), 013706 DOI: 10.7566/JPSJ.83.013706 Diamond Proposal Number(s): [7720] Show Abstract ▼ Abstract: 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 700 K is attributed in part to charge-like quadrupoles in a cycloid.	Dec 2013
Theoretical Physics	Polarization analysis in resonant x-ray Bragg diffraction by K2CrO4 at the CrK-edge J. Fernández-Rodríguez , S. W. Lovesey , J. A. Blanco Physical Review B 77 (9) DOI: 10.1103/PhysRevB.77.094441 Show Abstract ▼ Abstract: The creation of a circular polarization has been witnessed in resonant x-ray Bragg diffraction at the Cr K pre-edge (5.994 keV) of potassium chromate (K2CrO4). Interference between channels of diffraction and, specifically, the E1-E1, E2-E2, and E1-E2 channels provides an account of the observation. We report a theoretical analysis of polarization in the secondary beam for K2CrO4, with a variation of the primary linear polarization that successfully accounts for all aspects of the observations. An angular anisotropy of the local environment at Cr sites in this material is revealed in time-even quadrupoles, octupoles, and hexadecapoles that appear in scattering amplitudes for parity-even (E1-E1 and E2-E2) and parity-odd polar (E1-E2) channels. Our estimates of the multipoles derived from a fitting to the data for the secondary polarization are exploited in simulations of the diffracted intensity as a function of the azimuthal angle. There is a satisfactory agreement between simulations and the total intensity measured at space-group-forbidden (140) and (340) reflections.	Mar 2008
	Phase transitions, noncollinear magnetism, and magnetoelectric symmetry in gadolinium tetraboride S. W. Lovesey , J. Fernández Rodríguez , J. A. Blanco Rodriguez , P. J. Brown Physical Review B 70 DOI: 10.1103/PhysRevB.70.172414 Show Abstract ▼ Abstract: Resonant x-ray Bragg diffraction data for gadolinium tetraboride (GdB4), gathered at the Gd L3 edge above and below a transition temperature TN=42K, is shown to imply that a structural phase transition occurs at temperatures above the onset of long-range magnetic order in the Gd moments. Specifically, the room-temperature tetragonal structure P4∕mbm would appear to change to orthorhombic P21212, which is a continuous structural phase transition in Landau and renormalization-group theories. Below TN, a configuration of Gd moments is established, which is consistent with the magnetic Shubnikov group P21212, where moments are constrained to lie in the plane normal to the c axis. The crystal structure and magnetic point symmetry (222) inferred, is one of the class of 58 magnetic groups that can show the magnetoelectric effect.	Nov 2004

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