  We have used soft x-ray magnetic diffraction at the Fe3+ L2,3 edges to
examine to what extent the Dzyaloshinsky-Moriya interaction in Ba3NbFe3Si2O14
influences its low temperature magnetic structure. A modulated component of the
moments along the c-axis is present, adding to the previously proposed helical
magnetic configuration of co-planar moments in the a,b-plane. This leads to a
helical-butterfly structure and suggests that both the multi-axial in-plane and
the uniform out-of-plane Dzyaloshinsky-Moriya vectors are relevant. A non zero
orbital magnetic signal is also observed at the oxygen K edge, which reflects
the surprisingly strong hybridization between iron 3d and oxygen 2p states,
given the nominal spherical symmetry of the Fe3+ half filled shell.
