Abstract
Gd-ordering near 2.2 K in both superconducting and nonsuperconducting GdBa 2 Cu 3 O 7-y has been well documented. This report summarizes our results from comparative studies on other Gd-containing cuprates (with well-defined Néel temperatures in parentheses) including Bi 2 Sr 2 GdCu 2 O 8 (1.6 K), TlBa 2 GdCu 2 O 7 (2.2 K), TlSr 2 GdCu 2 O 7 (2.4 K), (Pb. 5 Cu. 5 )Sr 2 GdCu 2 O 7 (2.3 K), Pb 2 Sr 2 GdCu 3 O 8 (2.3 K), Gd 2 CuO 4 (6.6 K) and (Gd 1.85 Ce 0.15 )CuO 4 (5.3 K). The Néel temperature values for the Bi-, Tl-, and Pb-based cuprates remain close to that for PrBa 2 Cu 3 O 7-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 ΔS=Rln8 associated with the ordering. © 1994.