Effect of Ca substitution on crystal structure and superconducting properties of ferromagnetic superconductor RuSr2-xCaxGd1.4Ce0.6Cu2O10-delta
We have investigated the effect of Ca substitution for Sr site on structural, magnetic and superconducting properties of RuSr2-xCaxGd1.4Ce0.6Cu2O10-delta system. In this system, the magnetic coupling of RuO2 and CuO2 plays an important role in magnetic and superconducting states. X-ray diffraction analysis shows that all samples are single phase and the lattice parameters decrease continuously by increasing Ca content. The onset superconducting transition temperature is found to decrease with Ca substitution. As Ca content increases, rotation of the RuO6 octahedron increases and Ru-O(1)-Ru angle decreases. These variations strengthen the magnetic moments in the RuO2 planes. The enhancement of weak ferromagnetic component and hole trapping by Ru magnetic moments in RuO2 planes reduces the electrical conduction, and destroys the superconducting state in the system. Analysis of the resistivity data (rho) based on the hoping conduction mechanism, indicates a variation of the hoping exponent (p) across the magnetic transition at T-m. The hoping exponent p is not affected sharply by Ca concentration. (C) 2011 Elsevier B.V. All rights reserved.