MAGNETIC-PROPERTIES OF PRBA2CU2MO8-Y(M = TA, NB)

We have investigated the magnetic properties of PrBa2Cu2MO8-y, (PrBCMO) (M = Ta, Nb), in which MO6 octahedra replace the square planar Cu in the parent compound, PrBa2Cu3O7-y (PrBCO). Signature of an antiferromagnetic (AFM) transition at 9 K for Pr1.1Ba1.9Cu2.1Ta0.9O8-y (Pr1.1BCTO) and at 10 K for PrBa2Cu2NbO8-y (PrBCNO) is found in the magnetic susceptibility versus temperature curve. The value for the latter is somewhat lower than that observed recently. The transition temperatures are approximately half the value of 17 K observed for PrBCO. This transition in the absence Cu(1)-O(1) chains in PrBCMO means that it is due to the Pr sublattice ordering as confirmed recently. Our results also imply that the copper chains are not required for the ordering of the Pr sublattice. However, a reduction in T(N) indicates that the Cu(1)-O(1) chains, acting as separator layers between the CuO2 planes, may play a role. The effect of separator layers, Cu(1)-O(1)/MO6, on the Pr-containing block, CuO2-Pr-CuO2, is to change the double-layer CuO2 spacing, which in turn may control T(N) through hybridization effects. The Neel point seems to be related to this CuO2 interlayer spacing in Pr-based cuprates. The effective paramagnetic moment of the Pr ion is found to be 3.06 mu(B) and 2.85 mu(B), respectively, for Pr1.1BCTO and PrBCNO, a value somewhat higher than that found for PrBCO.