Crystal structures, magnetic and superconducting properties of the RuSr₂NdCu₂O_x and RuSr₂GdCu₂O_y compounds

We report the magnetization and the susceptibility measurements of the RuSr_2GdCu_2O_y and RuSr_2NdCu_2O_x perovskite materials. We find that RuSr_2GdCu_2O_y compound exhibits a magnetic transition at Tn=135 K followed by a superconducting one with an onset Tc=35 K. Samples of RuSr_2NdCu_2O_x material have shown neither superconductivity nor magnetic transition. XRD measurements show that in RuSr_2NdCu_2O_x the Nd ions tend to substitute to Sr ions in very high percentages. The relevance of this phenomenon on the absence of superconductivity in RuSr_2NdCu_2O_x is discussed.