Magnetic Properties of the Melilite-Type Oxysulfide Sr2MnGe2S6O: Magnetic Interactions Enhanced by Anion Substitution

The synthesis, crystal structures, photoluminescence, and magnetic properties of the melilite-type oxysulfide Sr2MnGe2S6O were investigated. This compound crystallizes in the melilite structure with space group P4̅21 m, in which two kinds of anions, S2– and O2–, occupy different crystallographic sites in an ordered manner. The temperature dependence of the magnetic susceptibility of Sr2MnGe2S6O shows a broad peak due to a two-dimensional magnetic interaction between Mn ions in the ab plane. The specific heat data show that this compound has an antiferromagnetic transition temperature (T N = 15.5 K) that is much higher than that of the oxide analogue Sr2MnGe2O7 (T N = 4.4 K). DFT calculations showed that the magnetic interaction is enhanced by covalency in the Mn–S bonding.