ac susceptibility investigation of vortex dynamics in nearly-optimally doped ReFeAsO1-xFx (Re = La, Ce, Sm) and Ba(Fe1-xCox)2As2 superconductors

In this contribution we will report about the dynamical features of the flux lines in both optimally-doped ReFeAsO1-xFx and Ba(Fe1-xCox)2As2 superconductors as investigated by means of ac susceptometry. The features of pinning are derived in the case of ReFeAsO1-xFx powder samples for several Re ions within the framework of the thermally-activated flux-creep model. In the case of the investigated Ba(Fe1-xCox)2As2 single-crystal, the extremely high-quality and the associated low-degree of quenched disorder in the sample allow us to enlighten the emergence of a thermodynamical phase transition between the different configuration of vortices in the H-T phase diagram. Insights are provided into the features of this phase transition and into the nature of the glassy phase, being turned into a Bragg-like glass at low values of magnetic field.