Analysis of the magnetic structure of the manganese oxychalcogenides R2Mn2Se2O (R=LaO,BaF) by density functional calculations

We examined the magnetic structures of R₂Mn₂Se₂O (R=LaO, BaF) by evaluating the spin exchange interactions on the basis of density functional theory (DFT) calculations, and compared how they differ from that of the Fe analog (BaF)₂Fe₂Se₂O. In R₂Mn₂Se₂O (R=LaO, BaF), the two-dimensional antiferromagnetic square lattice defined by J₁ is spin-frustrated, and the exchange J₁ is stronger for (LaO)₂Mn₂Se₂O than for (BaF)₂Mn₂Se₂O by a factor of 1.5 explaining why the magnetic susceptibility maximum occurs at a higher temperature for (LaO)₂Mn₂Se₂O than for (BaF)₂Mn₂Se₂O (360 vs. 210 K). We identified two probable reasons why the specific heat anomaly at the long-range antiferromagnetic ordering temperature T_N is significantly weaker for R₂Mn₂Se₂O than for (BaF)₂Fe₂Se₂O.