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

Systematic ac susceptibility measurements 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 energy U(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 similar to B-alpha with alpha = -0.46 is observed. The activation energy reaches 10(4) 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 alpha j(-0.1). Published by AIP Publishing.