MAGNETIC CORRELATIONS IN PR1-XYXBA2CU3O7 STUDIED BY MOSSBAUER-SPECTROSCOPY ON SUBSTITUTED YB-170(3+)

We have used Yb-170(3+) Mossbauer spectroscopy on Yb3+ diluted at the rare-earth sites in Pr1-xYxBa2Cu3O7 and in PrBa2Cu3O6 to examine the magnetic properties associated with the (hybridized) Pr3+ ions. Magnetic ordering in the non-superconducting compounds PrBa2Cu3O7 (T(N) = 16 K) and PrBa2Cu3O6 (T(N) = 10 K) is identified by the appearance of a Pr3+-derived molecular field and by a change in the Yb3+ paramagnetic relaxation rates. Evidence is presented suggesting the ordered Pr3+ magnetic moments are aligned well away from the c-axis. The splitting of the three lowest crystal-field levels in PrBa2Cu3O6 is estimated to be about half that (approximately 50 K) in PrBa2Cu3O7. In the superconducting samples of Pr1-xYxBa2Cu3O7, the Yb3+ local probes give evidence for an inhomogeneous behavior linked to statistical variations in the Pr3+/Y3+ occupancies. With increasing x, both the volume of the sample showing local Pr3+ magnetic order and the average ordering temperature decreases. There appears to be an anti-correlation between the superconducting transition temperature and the volume of the sample showing Pr3+ magnetic order, suggesting the local Pr3+ concentration needed to remove superconductivity (in favor of Cu(2)-based magnetic order) is near that needed to support local Pr3+ magnetic order.