Magnetoresistance, critical current density, and magnetic flux pinning mechanism in nickel doped BaFe2As2 single crystals

The critical current density, J_c, flux pinning behavior and magneto- resistance results of BaFe_2-xNi_xAs₂ single crystal have been investigated in fields up to 13 T over a temperature range of 2 to 20 K. The magnetoresistance below the superconducting transition temperature (T_c) shows Arrhenius thermally activated behavior: ρ = ρ_oexp(-U_o(T,H)/k_BT), where U_o is the thermally activated energy. BaFe_2-xNi_xAs₂ exhibits high thermally activated flux flow energy with a very weak field dependence. J_c is as high as 2 × 10⁵ A/cm² for zero magnetic field at 2 K. J_c was found to decrease for B < 1 T, but showed a very weak field dependence and remained nearly constant with increasing magnetic field for B > 1 T at T = 2, 5, and 10 K. Flux jumping was also observed in magnetization loops at very low temperature for large sample, which is related to the high J_c in the single crystal. A peak effect was observed at 10 K