Synthesis and physical properties of Ca₁₋<i>_xRE_x</i>FeAs₂with<i>RE</i>= La–Gd

Abstract

The synthesis of a series of layered iron arsenides Ca1-xRExFeAs2(112) was attempted by heating at 1000 degrees C under a high pressure of 2 GPa. The 112 phase successfully forms with rare earth (RE) = La, Ce, Nd, Sm, Eu, and Gd, while RE-free samples do not contain the 112 phase. While a Ce-doped sample does not show superconductivity, La-, Pr-, Nd-, Sm-, Eu-, and Gd-doped samples show superconducting transition temperatures of 24.5, 13.2, 11.9, 11.6, 9.3, and 12.6 K, respectively, in magnetization measurements. Their T-c and Fe-Fe interlayer distances decreased with decreasing ionic radii of RE, but there are exceptions.