Properties, magnetic susceptibility, critical currents and irreversibility fields of(Tl0.5Pb0.5)Sr2 (Ca1−xGdx)Cu2Oz bulk superconductors

Abstract

Bulk (Tl0.5Pb0.5)Sr2(Ca1−xGdx)Cu2Oz superconductors with x = 0.1,0.2 and 0.3 were prepared by a wet chemical gel technique followed by aspecial heat-treatment procedure. X-ray diffraction analysis revealedpractically phase-pure samples with tetragonal structure (space groupP/4mmm). The temperature dependence of the real and imaginary parts of the acsusceptibility and the dependence on the ac applied magnetic field wereinvestigated to learn about the superconducting and magnetic properties of bulk(Tl0.5Pb0.5)Sr2(Ca1−xGdx)Cu2Oz superconductors. The critical current densities of the samples were derived from Bean’smodel. The temperature dependence of the critical current was successfully fitted basedon a power law from the thermally activated magnetic flux creep model. Frommagneto-resistance measurements the temperature dependences of the transport criticalcurrents and the irreversibility fields were found. The dc magnetic field dependence of thewidth of superconducting transitions and the critical currents was also obtained. Theseproperties of the superconductors were analyzed within available theoretical models.