Flux-creep activation energy for a BaFe1.9Ni0.1As2 single crystal derived from alternating current susceptibility measurements.

Systematic acsusceptibilitymeasurements have been performed to investigate the vortex dynamics in a BaFe1.9Ni0.1As2 single crystal as a function of temperature, frequency, ac field amplitude, and dc magnetic field. The complex activation energyU(T,B,j) is derived in the framework of thermally activated flux creep theory and can be expressed in one simple formula. A power law dependence of U ~ Bα with α?=?-0.46 is observed. The activation energy reaches 104 K at low fields, suggesting strong pinning in the material. The nonlinear function of the activation energy vs. the current density is determined, which has the expression of U ∝j-0.1. [ABSTRACT FROM AUTHOR]