Systematic study of vortex pinning and a liquid–glass phase transition in BaFe$_{2-x}$Ni$_x$As$_2$ single crystals

The vortex pinning and liquid-glass transition have been studied in BaFe$_{2-x}$Ni$_x$As$_2$ single crystals with different doping levels ($x= 0.065, 0.093, 0.1, 0.14, 0.18$). We found that Ni-doped Ba-$122$ has rather narrow vortex-liquid state region. Our results show that the temperature dependence of the resistivity as well as $I-V$ characteristics of Ni-doped Ba-$122$ is consistent with $3\mathrm{D}$ vortex-glass model. It was found that -pinning gives the main contribution to overall pinning in $122$ Ni-doped system. The vortex phase diagrams for different doping levels were built based on the obtained data of temperature of the vortex-glass transition $T_g$ and the upper critical magnetic field $H_{c2}$.