Abstract
The anomalous Pr antiferromagnetic order with high Néel temperature T <sub>N</sub> (Pr) are reported throughout the whole Pr <sub>1+x</sub> Ba <sub>2-x</sub> Cu <sub>3</sub> O <sub>7-y</sub> or 1212-type Cu(Ba <sub>2-x</sub> Pr <sub>x</sub> )PrCu <sub>2</sub> O <sub>7-y</sub> system (-0.2<x<1; -0.4<y<1), where three distinct crystal structures were observed: orthorhombic 1212-chain O(I) (space group Pmmm), tetragonal T (P4/mmm), and orthorhombic O(II) (Cmmm). Systematic variation of T <sub>N</sub> (Pr) in this system as well as in other 1212 and 2212 cuprates M <sub>n</sub> A <sub>2</sub> PrCu <sub>2</sub> O <sub>7</sub> (n = 1, 2, M = Hg, Tl, Pb/Cu, Bi, Nb, Cu; A = Sr, Ba, Ba/Pr) was discussed through the correlation of T <sub>N</sub> (Pr) with Pr-O bond length. The importance of quasi-two-dimensional Pr-O-Pr superexchange magnetic coupling through strong wave function overlap between the overextended Pr-4f orbital with eight O-2p <sub>π</sub> orbitals in the adjacent CuO <sub>2</sub> bi-layer is discussed. No superconductivity was observed in the present study. © 2001 Elsevier Science Ltd. All rights reserved.