Title: Flux-flow and vortex-glass phase in iron pnictide BaFe$_{2-x}$Ni$_x$As$_2$ single crystals with $T_c$ $\sim$ 20 K,
Abstract: We analysed the flux-flow region of isofield magneto resistivity data
obtained on three crystals of BaFe$_{2-x}$Ni$_x$As$_2$ with $T_c$$\sim$20 K for
three different geometries relative to the angle formed between the applied
magnetic field and the c-axis of the crystals. The field dependent activation
energy, $U_0$, was obtained from the TAFF and modified vortex-glass models,
which were compared with the values of $U_0$ obtained from flux-creep available
in the literature. We observed that the $U_0$ obtained from the TAFF model show
deviations among the different crystals, while the correspondent glass lines
obtained from the vortex glass model are virtually coincident. It is shown that
the data is well explained by the modified vortex glass model, allowing to
extract values of $T_g$, the glass transition temperature, and $T^*$, a
temperature which scales with the mean field critical temperature $T_c(H)$. The
resulting glass lines obey the anisotropic Ginzburg-Landau theory and are well
fitted by a theory developed in the literature by considering the effect of
disorder.