Crystal Symmetry Lowering In Chiral Multiferroic Ba3tafe3si2o14 Observed By X-Ray Magnetic Scattering

Chiral multiferroic langasites have attracted attention due to their doubly chiral magnetic ground state within an enantiomorphic crystal. We report on a detailed resonant soft x-ray diffraction study of the multiferroic Ba3TaFe3Si2O14 at the Fe L-2,L-3 and oxygen K edges. Below T-N (approximate to 27K) we observe the satellite reflections (0,0, tau), (0,0,2 tau), (0,0,3 tau), and (0,0,1 - 3 tau) where tau approximate to 0.140 +/- 0.001. The dependence of the scattering intensity on x-ray polarization and azimuthal angle indicate that the odd harmonics are dominated by the out-of-plane ((c) over cap axis) magnetic dipole while the (0,0,2 tau) originates from the electron density distortions accompanying magnetic order. We observe dissimilar energy dependencies of the diffraction intensity of the purelymagnetic odd-harmonic satellites at the Fe L-3 edge. Utilizing first-principles calculations, we show that this is a consequence of the loss of threefold crystal symmetry in the multiferroic phase.