Upper critical magnetic field in a Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ and Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$

We report measurements of the temperature dependence of the radio frequency magnetic penetration depth in Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ and Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ single crystals in pulsed magnetic fields up to 60 T. From our data, we construct an $H$–$T$-phase diagram for the inter-plane ($H\parallel {c}$) and in-plane ($H\parallel {ab}$) directions for both compounds. For both field orientations in Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ we find a concave curvature of the $H_{c2}(T)$ lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we can describe $H_{c2}(T)$ and its anisotropy. In contrast, we find that Pauli paramagnetic pair breaking is not essential for Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$. For this electron-doped compound, the data support a $H_{c2}(T)$ dependence that can be described by the Werthamer–Helfand–Hohenberg model for $H\parallel{ab}$ and a two-gap behavior for $H\parallel {c}$.