Effect of Pr-O hybridization on the anomalous magnetic properties of Pr1+xBa2-xCu3O7-y system

The Pr L3-edge x-ray absorption near edge structure spectra and antiferromagnetic TN(Pr) data for the parent system PrBa2Cu3O7−y (0⩽y<1) and the oxygenated system Pr1+xBa2−xCu3O7−y (0⩽x⩽1; −0.27⩽y⩽0.05) are reported. The formal Pr valence in the PrO8 cage decreases from 3.18 for PrBa2Cu3O6.95 [TN(Pr)=18.5 K], to 3.12 for Pr1.2Ba1.8Cu3O6.98 (15.5 K), 3.03 for Pr1.6Ba1.4Cu3O7.16 (8 K), and 3.00 for Pr2BaCu3O7.27 [TN(Pr) not observed]. The Pr valence depends both on the number of holes available in the PrO8 cage and the Pr 4f-O 2pπ hybridization strength. On the other hand, anomalous TN(Pr) is a direct result of exchange interaction though Pr–O–Pr hybridization. However, the relative contribution from PrIV–PrIV superexchange via strong Pr–O orbital hybridization and PrIII–PrIII/PrIII–PrIV superexchange paths is unclear.