Upper critical field measured up to 85T in different iron-based compounds

We report magneto-transport measurements of H$_{c2}$(T) at very high dc and pulsed magnetic field up to 85T on different families of iron-based single crystals and thin film superconductors with different doping levels and stress. Some of these materials show high H$_{c2}$ extrapolating to $\sim $100T and extremely high slopes up to 20 T/K for H//c and over 200 T/K for H//ab, indicating significant Pauli pair breaking and a possibility of the Fulde-Ferrel-Larkin-Ovchinnikov state. The superconducting transitions remain sharp also at the highest field showing an irreversibility field close to H$_{c2}$.