Magnetic and structural properties of the iron oxychalcogenides La 2 O 2 Fe 2 O M 2 ( M = S , Se )

In this paper, we present the results of structural and magnetic phase comparisons of the iron oxychalcogenides La2O2Fe2OM2 (M = S, Se). Elastic neutron scattering reveals that $M$ = S and Se have similar nuclear structures at room and low temperatures. Both materials obtain antiferromagnetic ordering at a Neel temperature $T_{N}$ 90.1 $\pm$ 0.16 K and 107.2 $\pm$ 0.06 K for $M$ = Se and S, respectively. The magnetic arrangements of $M$ = S, Se are obtained through Rietveld refinement and we present the first direct comparison of magnetic structural analysis for these materials. We find the order parameter exponent $\beta$ to be 0.129 $\pm$ 0.006 for $M$ = Se and 0.133 $\pm$ 0.007 for $M$ = S. Each of these values is near the Ising symmetry value of 1/8. Lastly, this suggests that although lattice and electronic structural modifications result from chalcogen exchange, the nature of the magnetic interactions is similar in these materials.