Upper critical field, critical current density and thermally activated flux flow in fluorine doped CeFeAsO superconductors

We report our studies on the crystal structures, morphologies, and superconductivity in CeO1 − xFxFeAs compounds which were fabricated by solid state reaction. The crystal structures were refined using Rietveld refinement. Superconducting properties such as critical temperature (Tc), critical current density (Jc), and upper critical field (Hc2) were determined using magneto-transport and magnetic measurement over a wide range of temperature below Tc, and in magnetic fields up to 13 T. Jc is 2 × 103 A cm − 2 for the x = 0.1 sample. However, the Jc exhibited a weak dependence on magnetic field for B > 1 T and T = 5 and 10 K. A peak effect in the Jc as a function of field was observed at 20 K in the x = 0.1 sample. We estimate Hc2ab of 185 T for CeO0.9F0.1FeAs compound. The broadening of the superconducting transition near Tc with increasing field can be well understood using the thermal activated flux flow model. The pinning potential scales as Uo/KB x B-n with n = 0.2 for B < 3 T and n = 0.71 for B > 3 T in the x = 0.1 sample.