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.