Doping dependence and high-pressure studies on Eu_x Ca_{1 - X} Fe₂As₂(0 ≤x ≤ 1)

We have investigated the electrical transport and magnetic properties of Eu x Ca1 - x Fe2As2 (ECFA) (0 ≤x ≤ 1) at ambient and under high-pressure. Temperature dependence of resistance shows a distinct anomaly at T SDW ∼ 165 - 190 K due to the spin density wave (SDW) transition. Initially, T SDW increases rapidly with x up to 0.45, and then more slowly at higher x until it saturates at T SDW ∼ 190 K for x = 1. Also, there exists another transition at low temperature, T N ∼ 10 - 20 K, due to the antiferromagnetic order of Eu2 + spins. Magnetic susceptibility follows the Curie-Weiss, 1/T behavior. However, it does not show clear evidence of T SDW while exhibiting a sharp anomaly at T N . The T N 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, T c ∼ 19 K is induced in the ECFA samples (x = 0.14, 0.31, and 0.45). We have studied the pressure dependence of T c and T SDW , and we present the pressure-temperature phase diagram.