CRYSTAL-STRUCTURE AND MAGNETIC-ORDERING OF PR IN (PB0.5CU0.5)(2)(BA0.5SR0.5)(2)PRCU2O8

The crystal structure of polycrystalline PbBaSrPrCu3O8 was studied usi ng high resolution neutron diffraction. Rietveld refinement of the dif fraction pattern shows that the compound crystallizes into the Tl2Ba2Y Cu2O8 2212-type structure. The Pb and Cu atoms in the two (Pb,Cu)O lay ers are randomly mixed to form two (Pb0.5Cu0.5)O layers, and the Pa an d Sr atoms are also randomly mixed to form two (Ba0.5Sr0.5)O layers, r esulting in (Pb0.5Cu0.5)(2)(Ba0.5Sr0.5)(2)PrCu2O8. The magnetic orderi ng of the Pr ions was also studied using magnetic neutron diffraction and ac susceptibility measurements. At low temperatures, magnetic peak s presumably originating from the Pr spin ordering were observed at th e {1/2 1/2 1/2 1/2}, {1/2 1/2 3/2}, and {1/2 1/2 5/2} positions. The P r spins order at T-N approximate to 9 K with the moment direction alon g the c axis and the nearest-neighbor spins coupled antiferromagnetica lly. A cusp associated with the antiferromagnetic ordering at T-N is a lso clearly observed in ac susceptibility measurements. (C) 1997 Ameri can Institute of Physics.