The normal state and superconducting properties are investigated in the phase diagram of K_xSr_{ 1-x}Fe_2As_2 for 0<x<1. The ground state upper critical field, H_{ c2}(0), is extrapolated from magnetic field dependent resistivity measurements. H_{ c2}(0) scales with the critical temperature, T_c, of the superconducting transition. In the normal state the Seebeck coefficient is shown to experience a dramatic change near a critical substitution of x=0.3. This is associated with the formation of a spin density wave state above the superconducting transition temperature. The results provide strong evidence for the reconstruction of the Fermi surface with the onset of magnetic order.
Categories: cond-mat.supr-con cond-mat.str-el