Inter- and Intra-granular flux Pinning in Ba(Fe0.91Co0.09)2As2 Superconductors☆

Abstract Thermally assisted flux flow (TAFF) and flux pinning energiesare studied in a Ba(Fe 0.91 Co 0.09 ) 2 As 2 ( T c = 25.3 K) sample via resistivity and AC susceptibility measurements in magnetic fields up to 18T. The flux pinning energy U ( T,H ) is determined from the Arrhenius law. The pinning maxima well determined by resistivity measurements ranged from 1724 K at 0 T to 585 K at 18 T with a sharp drop off so that U(T=T c ) varied with the applied field H as . The pinning activation energies determined from the AC susceptibility data but were by a factor of three higher, which is explained here. Both inter- and intra-granular pinning energies are determined in low fields. The onset of TAFF temperature and the crossover temperature T x from TAFF to flux flow are determined, showing the limitations of the Anderson-Kim model.