Dependence of the flux-creep activation energy on current density and magnetic field for a Ca-10(Pt3As8)[(Fe1-xPtx)(2)As-2](5) single crystal

We have performed detailed ac susceptibility measurements to investigate the vortex dynamics in a Ca10(Pt3As8)[(Fe 1-xPtx)2As2]5 single crystal as a function of temperature, frequency, ac amplitude, and dc field. The field dependence of the activation energy U is derived in the framework of thermally activated flux creep theory, yielding a power law dependence of U ∼ Hα with α≈ -1.0 for H above 0.30 T, while below 0.3 T U is independent of the field. 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 shows logarithmic dependence U(J). © 2014 AIP Publishing LLC.status: publishe