Single Crystals*

We have carried out systematic electrical transport and magnetic properties of Eu_xCa_1-xFe₂As₂ (ECFA) single crystals. The resistance shows a clear anomaly due to the spin-density wave (SDW) at T_SDW ~ (165-190 K) and it varies systematically with the doping level (x). There exists another transition at low-temperature T_N ~ (15-20 K) due to the antiferromagnetic order of Eu²⁺ spins. T_N also shows a systematic dependence with x. At ambient pressure, none of the ECFA samples show superconducting properties. Therefore, we have used a high-pressure technique to induce superconductivity, and superconductivity with T_c ~ 19 K is induced under ~19 kbar applied pressure. The pressure dependence of T_c and pressure-temperature phase diagram will be discussed.