Investigation of the magnetic field angle dependence of resistance, irreversibility field, upper critical field and critical current density in DC sputtered Bi-2223 thin film

Abstract

We measured resistivity and transport critical current density, J c , as a function of DC magnetic field and the angle ( ϕ) between the surface of the film and the magnetic field on ex-situ annealed, c-axis oriented Bi-2223 thin films fabricated by DC sputtering method. Irreversibility field ( μ 0 H irr ) and upper critical field ( μ 0 H c2 ) were determined from the resistivity versus the applied magnetic field graph. It is observed that critical temperature ( T c ), μ 0 H irr, μ 0 H c2 and J c of the films strongly depend on the direction and strength of the field. While T c of the film without magnetic field is observed to be about 102 K, it is found to decrease to 90 K (85 K) for the applied field perpendicular (parallel) to c-axis of the film. Not only were μ 0 H irr (0) and μ 0 H c2 (0) values determined from the μ 0 H irr and μ 0 H c2 versus temperature graphs, respectively, but also penetration depths and coherence lengths were interpreted. Anisotropy of the film was also discussed by means of the change of irreversibility as a function of angle. Moreover at 4.2 K, J c was observed to be 3000 A/cm 2 at zero field; however, it was found to abruptly decrease to 1982 (1 1 2 0) A/cm 2 under low magnetic field at ϕ=0° ( ϕ=90°), which indicates that anisotropic J c behavior of the film is intrinsic. Furthermore, we provided a theoretical analysis of the obtained results in the framework of intrinsic pinning theory of superconductors. Microstructural properties of the produced films were also reinvestigated by X-ray diffractometer (XRD) and scanning electron microscopy (SEM) measurements. XRD patterns indicate that the films are c-axis oriented based on the prominent (0 0 l) peaks. SEM images show needle-like grain structures dominate the surface morphology of the films.