ANOMALOUS PR-ORDERING IN HIGH-T-C CUPRATE SYSTEMS

The systematic variation of anomalous Pr antiferromagnetic ordering fo r the two-CuO2-layer 1212 cuprate system MA(2)PrCu(2)O(7) (M = Hg, Pb, Tl, Cu, Nb; A = Sr, Ba) was verified through the variation of Neel te mperature T-N(Pr) with Pr-O bond length and Pr minimum magnetic entrop y S-m. The importance of quasi-2D Pr-O-Pr superexchange magnetic coupl ing through the strong hybridization between the Pr-4f and the eight O -2p(pi) orbitals in the adjacent CuO2 layers is expected for all two-C uO2-layer M(m)A(2)PrCu(2)O(y) m212-type (m = 1,2,3) compounds, and sim ilarly anomalous Pr compounds were observed in M(2)A(2)PrCu(2)O(8) and M(3)A(2)PrCu(2)O(8) (M = Pb, Cu; A = Ba, Sr). The only case with abse nce of long rang T-N(Pr) down to 1.4 K was in the incommensurate modul ated Bi-2212 compound Bi2Sr2PrCu2O8+delta.