COMPARATIVE-STUDIES OF GD-ORDERING IN VARIOUS CUPRATE SYSTEMS

Gd-ordering near 2.2 K in both superconducting and nonsuperconducting GdBa2Cu3O7-y has been well documented. This report summarizes our results from comparative studies on other Gd-containing cuprates (with well-defined Neel temperatures in parentheses) including Bi2Sr2GdCu2O8 (1.6 K), TlBa2GdCu2O7 (2.2 K), TlSr2GdCu2O7 (2.4 K), (Pb.5Cu.5)Sr2GdCu2O7 (2.3 K), Pb2Sr2GdCu3O8 (2.3 K), Gd2CuO4 (6.6 K) and (Gd1.85Ce0.15)CuO4 (5.3 K). The Neel temperature values for the Bi-, Tl-, and Pb-based cuprates remain close to that for PrBa2Cu3O7-y having similar layered structures but somewhat different Gd-Gd distance along the c-axis, whereas the T'(214) compounds become ordered at higher temperatures. Also to be noted is the general occurrence of a broad shoulder below the heat capacity peak, which needs to be taken into account for obtaining the expected magnetic entropy DELTAS = Rln8 associated with the ordering.