  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.
