The magnetism of Sr${}_2$F${}_2$Fe${}_2$OS${}_2$ was examined through neutron powder diffraction and thermodynamic and transport measurements. Quasi-two-dimensional magnetic order develops below $T_N=106\left(2\right)$ K with an in-plane correlation length exceeding 310 Å and an out-of-plane correlation length of just 17(3) Å. The data are consistent with a two-k structure with ${\mathbf{k}}_1=(1/2,0,1/2)$ and ${\mathbf{k}}_2=(0,1/2,1/2)$ and an ordered moment of 3.3(1)${\mu }_B$ oriented along the in-plane components of k. This structure is composed of orthogonal antiferromagnetic chains intersecting at superexchange-mediating O sites. Density functional theory also points to this structure and a narrower Fe 3$d$ band than for the iron pnictides from which electronic correlations produce a Mott insulator.

• Received 5 October 2012

DOI:https://doi.org/10.1103/PhysRevB.87.020406