Effect of annealing and granularity on the physical properties of GdSr 2RuCu 2O 8

Abstract

The variation of crystallite size (coherent domains as measured from X-ray analysis) and the physical properties of the ferromagnetic superconductor GdSr 2RuCu 2O 8 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 °C leads to an increase in grain and crystallite sizes and a decrease in the superconducting transition width Δ T c. The derivative of resistivity with respect to temperature, d ρ/d T, shows two peaks at T 1 and T 2 (with T 1 > T 2), which can be attributed to the onset of intra-granular and inter-granular superconductivity, respectively. T 2 increases drastically on increasing the annealing time, whereas only a marginal increase is observed in T 1. On the contrary, there is no apparent change in the thermodynamic transition temperature T th. The temperature dependence of the normal state resistivity, ρ( 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 H c1 J , respectively.