Phase Diagram As A Function Of Doping Level And Pressure In The Eu1-Xlaxfe2as2 System

We establish the phase diagram of the Eu1-x LaxFe2As2 system as a function of doping level x and pressure by measuring the resistivity and magnetic susceptibility. Increased pressure can suppress the spin-density-wave (SDW) and structural transitions very efficiently, while enhancing the antiferromagnetic (AFM) transition temperature T-N of Eu2+. Superconductivity coexists with SDW order at low pressure and always coexists with Eu2+ AFM order. The results suggest that the Eu2+ spin dynamics is unconnected with the superconducting pairing taking place in the two-dimensional Fe-As plane, but it can strongly affect superconducting coherence along the c axis.