Experimental Study of Partial Substitution of Copper with 3d Elements in "123" Superconductors.

About forty superconducting samples of Y and Sm, doped with different concentrations of Mn, Fe, Co, Ni and Zn, were prepared. These samples were characterized by x-ray diffractometry, microprobe analysis, resistance measurements, and SQUID susceptometry. Emphasis was given to the magnetic aspects of the specimens. Two standard procedures were followed with each sample. Mainly, the zero field cooling procedure (ZFC) and the field cooling procedure (FC). In both cases, the magnetic moment was measured at different temperatures after the sample was thermalized. Paramagnetic behavior above rm T _{c} was observed in all the cases. The experimental results were fitted to the Curie-Weiss law, by using SAS (Statistical Analysis System) programs. From this analysis, a range for the effective magnetic moments of the dopant ions was calculated. Also, the density of states at the Fermi level per Cu ion and the Sommerfeld constants were found for each case. In general, lower transition temperatures and higher density of states rm D(varepsilon _{b}F) for Sm doped specimens were observed. The variation of the density of states or gamma with the doping has also been analyzed as a function of N. We notice gamma to be linear in N about rm N_{max }. Samarium doped samples showed a larger gamma, but the slope alpha = (rm dgamma/dN) was generally not rare earth dependent. alpha did not correlate with beta = (rm dt_{c}/dN). It was found that beta(Zn) ~ beta(Mn). This decrease in gamma at rm N_{max} was not anticipated in the Matthias' rule. This finding was one of the most important results of the present research.