Superconductivity and critical current density in LaFeAsO_{1 - X}F_x compounds

Here, we report our studies on the crystal structures, morphologies, and superconductivity in LaFeAsO_{1 - x}F_x compounds which were fabricated by solid state reaction. The crystal structures were refined using Rietveld refinement. Superconducting properties, such as critical temperature, T_c, critical current density, J_c, and upper critical field, H_c2, were determined using magneto-transport and magnetic measurements over a wide range of temperature below and above T_c, and in magnetic fields up to 14 T. A peak effect in the J_c versus field is observed at T < 15 K. Upper critical field in the ab and c directions is H^ab_c2 = 122.8 T and H^c_c2 = 38.6 T, respectively.