Unusual Pr antiferromagnetic ordering in high-T_c cuprates

The anomalous Pr antiferromagnetic order with high Néel temperature T_N(Pr) are reported throughout the whole Pr_1+xBa_2-xCu₃O_7-y or 1212-type Cu(Ba_2-xPr_x)PrCu₂O_7-y 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_N(Pr) in this system as well as in other 1212 and 2212 cuprates M_nA₂PrCu₂O₇ (n = 1, 2, M = Hg, Tl, Pb/Cu, Bi, Nb, Cu; A = Sr, Ba, Ba/Pr) was discussed through the correlation of T_N(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_π orbitals in the adjacent CuO₂ bi-layer is discussed. No superconductivity was observed in the present study.