Doping dependence and high-pressure studies on EuxCa1-xFe2As2 (0 < x < 1)

We have investigated the electrical transport and magnetic properties of EuxCa1-xFe2As2 (ECFA) (0 < x < 1) at ambient and high pressures. Temperature dependence of resistance shows a distinct anomaly at TSDW ~ 165 - 190 K due to the spin density wave (SDW) transition. Initially, TSDW increases rapidly with x up to 0.45, and then more slowly at higher x until it saturates at TSDW = 191 K for x = 1. Also, there exists another transition at low temperature, TN ~ 10 - 20 K, due to the antiferromagnetic ordering of Eu2+ spins. Magnetization does not show clear evidence of TSDW while exhibiting a sharp anomaly at TN. The TN values in both the resistance and magnetization measurements are comparable to one another and vary linearly with x. At ambient pressure, none of the ECFA samples show properties of superconductivity down to 1.8 K. With the application of external pressure, the SDW order is gradually suppressed and superconductivity with a critical temperature as high as, Tc ~ 19 K is induced in the ECFA samples (x = 0.14, 0.32, and 0.45). We have studied the pressure dependence of Tc and TSDW, and we present the pressure-temperature phase diagram.