Magnetic structure of GdB4 from spherical neutron polarimetry

Interest in the antiferromagnetic ordering on GdB4 has been recently renewed by the observation of interference between magnetic and anisotropic charge contributions obtained from resonant x-ray scattering experiments at the Gd L-3 edge. Models accounting for the x-ray experiments with collinear and noncollinear Gd magnetic moments are almost indistinguishable from the experimental data available. However, the ambiguity between the different arrangements can be resolved directly and much more easily using spherical neutron polarimetry. The present findings show that the Gd moments order noncollinearly in a structure with the Shubnikov magnetic space group P4/m(')b(')m('), which has magnetoelectric symmetry.