Abstract
The systematic variation of anomalous Pr antiferromagnetic ordering temperature T N (Pr) for the two-CuO 2 -layer cuprate system MA 2 PrCu 2 O y (M=Cu, Hg, Tl, Pb; A=Ba, Sr) was verified through the observation of a new Hg-1212 HgSr 2 PrCu 2 O 6+δ tetragonal compound with a T N (Pr) of 6 K and a Pr-O bond length of 2.492 Å between Pr and oxygen in the adjacent CuO 2 layers. For the tetragonal/orthorhombic 1212 compounds including the PrBa 2 Cu 3 O 7-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-CuO 2 -layer M m A 2 PrCu 2 O y w212-type (m=1, 2, 3) compounds. A similar Pr anomaly in the 2212-type system was first observed on the new tetragonal (Pb 0.5 Cu 0.5 ) 2 (Ba 0.5 Sr 0.5 )2PrCu 2 O 8 compound with a high T N (Pr) of 9 K. © 1996 American Institute of Physics.