Crystal Structures and Magnetic Properties of New Europium Melilites Eu₂MSi₂O₇ (M = Mg, Mn) and Their Strontium Analogues

Synthesis, crystal structures, and magnetic properties of melilite-type oxides A2MSi2O7 (A = Sr, Eu; M = Mg, Mn) were investigated. These compounds crystallize in the melilite structure with space group P4̅21m. The 151Eu Mössbauer measurements show that the Eu ions are in the divalent state. The Eu2MgSi2O7 is paramagnetic down to 1.8 K. Long-range antiferromagnetic ordering is observed at 3.4 K for Sr2MnSi2O7. On the other hand, the Eu2MnSi2O7 shows a ferrimagnetic transition at 10.7 K. From the magnetization and specific heat measurements, it is found that the Eu2+ (14 μB) and Mn2+ (5 μB) sublattices order antiferromagnetically. This result indicates that an interaction between f-d electrons (Eu−Mn) predominantly operate in this compound.