Mixed-state Hall effect and flux pinning in Ba(Fe1-xCox)2As2 single crystals (x=0.08 and 0.10)

Longitudinal and Hall resistivities, scaling behavior, and magnetizations are examined to study the effect of flux pinning in Ba(Fe1-xCox)(2)As-2 (BFCA) single crystals with x = 0.08 and 0.01. Larger values of activation energy, critical current density, and pinning force are obtained in BFCA with x = 0.10, indicating relatively strong pinning. The sign reversal of Hall resistivities is clearly observed in BFCA with x = 0.10. The correlation between longitudinal and Hall resistivities shows the scaling behavior of rho(xy) proportional to (rho(xx))(beta) with exponents beta = 3.0-3.4 and 2.0+/-0.2 for BFCA crystals with x = 0.08 and 0.10, respectively. Furthermore, the normal-state Hall angle is also observed to follow cot theta(H) = Lambda T-2 + C in BFCA crystals, and is explained by the Anderson theory. The relatively large C/Lambda value for BFCA with x = 0.10 also implies a larger contribution of impurity scattering due to more Co atoms, which may cause stronger pinning of flux lines. The results are analyzed and coincide with theory, including the pinning-induced backflow effect and plastic flow mechanism in vortex dynamics.