Superconductivty and magnetic properties of $(Ru_{1-x}Nb_x)Sr_2(Sm_{1.4}Ce_{0.6})Cu_2O_z$

We investigated the effect of Nb substitution for Ru on the structural and magnetic properties of (Ru1-xNbx) Sr2(Sm1.4Ce0.6)Cu2Oz Samples. X-ray diffraction measurements indicated that nearly single-phase samples are formed in the range from x = 0 to 1.0. The superconducting transition temperature determined from the inflection in the field-cooled magnetic susceptibility decreased only slightly from Tc = 25 K for x = 0 to Tc = 22 K for x = 1.0, in consistent with the change in room temperature thermopower of the samples. However, the Nb substitution for Ru above x = 0.25 significantly suppressed the weak ferromagnetic component of the field-cooled magnetic susceptibility. It was also found that the Nb substitution for Ru results in an enhanced diamagnetic susceptibility with Nb content above x = 0.5 in both zero field-cooled and field-cooled magnetization measurements, in contrast to the behavior of the samples with x ≤ 0.5 in which the diamagnetic susceptibility decreases as the Nb content increases.