Magnetic and structural properties of the iron oxychalcogenides La2 O2Fe2 OM2 (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 Néel temperature TN90.1±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 β 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