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[en] The appearance of impurity phases belonging to the quaternary oxide system SrO-GdO_1.5-CuO-RuO₂ in Ru-1212 samples is difficult to avoid. While the formation of the ferromagnetic compound SrRuO₃ may be suppressed by a precursor route involving Sr₂GdRuO₆, this latter compound shows magnetization anomalies below 30 K. We present evidence that magnetization anomalies observed for some Ru-1212 samples in this temperature range are not due to trace amounts of Sr₂GdRuO₆. Rather, the effect appears to be related to the establishment of inter-granular superconductivity and to the vortex dynamics in Ru-1212

[en] The layered rutheno-cuprates RuSr₂LnCu₂O₈ (Ru-1212 structure) and RuSr₂(Ln_1+xCe_1-x)Cu₂O₁₀ (Ru-1222 structure; Ln=lanthanide or Y for both structures) consist of pairs of CuO₂ planes alternating with perovskite-like sheets of vertex sharing RuO₆ octahedra. Samples of Ru-1212 and Ru-1222 materials were known to show both superconducting and magnetic transitions. However, these perovskite-like sheets are also the characteristic structural feature of some strontium ruthenates. The presence of such impurity phases and an apparent dependence of superconducting and magnetic properties on sample preparation conditions made it difficult to attribute the ordering phenomena to the Ru-1212 and Ru-1222 phases. Here we report on investigations of the phase equilibria in the system Sr-Gd-Ru-Cu-O and on a precursor route to the synthesis of RuSr₂GdCu₂O₈ involving Sr₂GdRuO₆ and CuO. (orig.)