Effect of annealing and granularity on the physical properties of GdSr2RuCu2O8

• Published in: Physica. C, Superconductivity Superconductivity, 2006-09, Vol.443 (1-2), p.69-76
• Main Authors: GEETHA KUMARY, T, JANAKI, J, SASTRY, V. S, HARIHARAN, Y, VALSAKUMAR, M. C
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Granular, melt-textured, amorphous and composite superconductors; Inhomogeneous superconductors and superconducting systems; Physics; Properties of type I and type II superconductors; Superconductivity; Transport properties (electric and thermal conductivity, thermoelectric effects, etc.)
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2006.05.057

The variation of crystallite size (coherent domains as measured from X-ray analysis) and the physical properties of the ferromagnetic superconductor GdSr2RuCu2O8 on increasing the oxygen annealing time has been studied by X-ray analysis, SEM, resistivity and ac susceptibility measurements. Prolonged annealing in oxygen atmosphere at 1060 deg C leads to an increase in grain and crystallite sizes and a decrease in the superconducting transition width DeltaTc. The derivative of resistivity with respect to temperature, drho/dT, shows two peaks at T1 and T2 (with T1 > T2), which can be attributed to the onset of intra-granular and inter-granular superconductivity, respectively. T2 increases drastically on increasing the annealing time, whereas only a marginal increase is observed in T1. On the contrary, there is no apparent change in the thermodynamic transition temperature Tth. The temperature dependence of the normal state resistivity, rho(T), showed a gradual change from semiconducting-like to metallic behavior on increasing the annealing time. The variation in resistivity and the reduction in superconducting transition width can be attributed to the increase in grain size and the better inter-grain coupling achieved by increasing the annealing time. A large reduction in the diamagnetic signal on powdering and a broadening of the susceptibility transition on increasing the measuring field are observed in this compound. This can be attributed to the large penetration depth compared to the particle size and the small inter-granular lower critical field Hc1J, respectively.