OBSERVATION OF PR AND GD ORDERING IN THE 2212-TYPE COMPOUNDS (PB0.5CU0.5)(2)(BA0.5SR0.5)(2)RCU(2)O(8) (R=PR,GD)

Magnetic and calorimetric measurements have been made to reveal a Pr ordering in the (Pb0.5Cu0.5)(2)(Ba0.5Sr0.5)(2)PrCu2O8 compound which has the (Pb,Cu)-2212-type tetragonal structure with lattice parameters a = 3.878(3) Angstrom and c = 27.594(9) Angstrom. The transition occurs at a relatively high T-N(Pr) of 9 K. In comparison, isostructural (Pb0.5Cu0.5)(2) (Ba0.5Sr0.5)(2)GdCu2O8 exhibits a T-N(Gd) of only 2.2 K. The magnetic entropy associated with the Pr ordering has a lower limit value equivalent to about 20% of Rln3 expected for pr(3+) With a quasitriplet ground state, suggesting a more three-dimensional-like process. These results represent the observation of anomalous Pr ordering in the 2212-type cuprate and a complete demonstration of such effects in all two-CuO2-layer m 212 (m = 1,2,3) systems.