Circularly Polarized X Rays as a Probe of Noncollinear Magnetic Order in Multiferroic TbMnO3 (vol 102, 237205, 2009) - Fabrizi, F; Walker, H; Paolasini, L; de Bergevin, F; Boothroyd, A; Prabhakaran, D; McMorrow, D (Physical Review Letters, 2011)