Transport characterization and pinning analysis of BaFe1.9Ni0.1As2.05 thin films

Abstract

We report on the vortex-glass transition and superconducting performance of BaFe1.9Ni0.1As2.05 thin films with Tc = 17.8 K on CaF2(00l) single crystals by pulsed laser deposition. Atomic force microscopy characterization indicates the volumes of droplets appearing on the film surface increase with thickness and Magneto-optical imaging proves slight inhomogeneities in the current flow within the ab-plane of thin film. The thin films show a transport current density Jc of ∼1.14 MA cm−2 in self-field, and 0.34 and 0.28 MA cm−2 for H//c and H//ab up to 9 T at 4.2 K. Pinning mechanism associated with the fluctuations in the mean free path of the charge carries is found to be dominant in the thin films. The vortex-glass (VG) to vortex-liquid phase transition is identified in terms of the plots of the logarithmic derivative of the resistivity curves under different fields, allowing us to deduce the values of the VG transition temperature Tg, and the critical exponent s. The ρ–T curves are well scaled by VG theory. A phase diagram combining the VG transition temperature, irreversibility field and upper critical field is constructed.