  The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour
and we report here a neutron diffraction investigation into the magnetic
ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the
anti-Sr2MnO2Sb2-type structure and orders antiferromagnetically below TN = 105
K. We consider both its long-range magnetic structure and its magnetic
microstructure, and the onset of magnetic order. It adopts the multi-k vector
"2k" magnetic structure (k = (0.5 0 0.5) and k = (0 0.5 0.5) and has
similarities with related iron oxychalcogenides, illustrating the robust nature
of the "2k" magnetic structure.
