Upper critical field in Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ and FeSe$_{1-x}$ Te$_{x}$ compounds

We report H$_{c2}$ measurements in high magnetic field up to 31 T on Ba(Fe$_{1-x}$Co$_{1-x})_{2}$As$_{2}$ and FeSe$_{1-x}$ Te$_{x}$\textbf{ }pnictide compounds for different doping levels. Both materials exhibit a very high upper critical fields and unconventional temperature dependencies of H$_{c2}$(T) with the extremely high slopes dH$_{c2}$/dT from 10 to 30 T/K near T$_{c}$ and a relatively low anisotropy: $\gamma ={H_{c2} ^{//}} \mathord{\left/ {\vphantom {{H_{c2} ^{//}} {H_{c2} ^\bot }}} \right. \kern-\nulldelimiterspace} {H_{c2} ^\bot }$ for the doped ternary compound and $\gamma \approx 1.1\div 1.2$ for the binary one. The observed temperature dependences of H$_{c2}$(T) and the high H$_{c2}$ values well above the BCS paramagnetic limit indicate the importance of the Zeeman pairbreaking effects in these compounds.