Systematic variation of TN(Pr) for the two-CuO2-layer cuprate m212 (m=1, 2, 3) systems

The systematic variation of anomalous Pr antiferromagnetic ordering temperature T N (Pr) for the two‐CuO2‐layer cuprate system MA2PrCu2O y (M=Cu, Hg, Tl, Pb; A=Ba, Sr) was verified through the observation of a new Hg‐1212 HgSr2PrCu2O6+δ tetragonal compound with a T N (Pr) of 6 K and a Pr—O bond length of 2.492 A between Pr and oxygen in the adjacent CuO2 layers. For the tetragonal/orthorhombic 1212 compounds including the PrBa2Cu3O7−y system, T N (Pr) was found to decrease monotonically with increasing Pr—O distance. The importance of Pr‐O‐Pr superexchange magnetic coupling is expected for all two‐CuO2‐layer M m A2PrCu2O y m212‐type (m=1, 2, 3) compounds. A similar Pr anomaly in the 2212‐type system was first observed on the new tetragonal (Pb0.5Cu0.5)2(Ba0.5Sr0.5)2PrCu2O8 compound with a high T N (Pr) of 9 K.