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

AbstractThermally assisted flux flow (TAFF) and flux pinning energiesare studied in a Ba(Fe0.91Co0.09)2As2 (Tc = 25.3K) 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 1724K at 0 T to 585K at 18 T with a sharp drop off so that U(T=Tc) 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 Tx from TAFF to flux flow are determined, showing the limitations of the Anderson-Kim model