Magnetic and structural properties of the iron oxychalcogenides La2O2Fe2OM2 (M = S, Se)

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. Our neutron diffraction data reveals that both materials obtain antiferromagnetic ordering at a Neel temperature T-N 90.1 +/- 0.16 K and 107.2 +/- 0.06 K for M = Se and S, respectively. The magnetic arrangements for both M = S, Se compounds are obtained through Rietveld refinement. We find the order parameter exponent beta to be 0.129 +/- 0.006 for M = Se and 0.133 +/- 0.007 for M = S. Each of these values is near the Ising symmetry value of 1/8. This suggests that although lattice and electronic structural modifications result from chalcogen replacement, the nature of the magnetic interactions is similar in these materials.