Superconducting properties of Ba(Fe1-xNix)2As2 thin films in high magnetic fields

We report on electrical transport properties of epitaxial Ba(Fe1-xNix)2As2 thin films grown by pulsed laser deposition in static magnetic fields up to 35 T. The thin film shows a critical temperature of 17.2 K and a critical current density of 5.7x10^5 A/cm^2 in self field at 4.2 K while the pinning is dominated by elastic pinning at two-dimensional nonmagnetic defects. Compared to single-crystal data, we find a higher slope of the upper critical field for the thin film at a similar doping level and a small anisotropy. Also an unusual small vortex liquid phase was observed at low temperatures, which is a striking difference to Co-doped BaFe2As2 thin films.
Comment: Accepted for publication in Applied Physics Letters, 5 figures