Co-doping Effects on Magnetism and Superconductivity in the 112-Type EuFeAs2 System

The discovery of EuFeAs 2 , currently the only charge-neutral parent phase of the 112-type iron-pnictide system, provides a new platform for the study of elemental doping effects on magnetism and superconductivity (SC). In this study, a series of polycrystalline EuFe 1− y Co y As 2 and Eu 0.9 Pr 0.1 Fe 1− y Co y As 2 samples are synthesized through solid-state reaction, and the evolutions of SC and magnetism with Co doping in EuFeAs 2 and Eu 0.9 Pr 0.1 FeAs 2 are investigated by electrical transport and magnetic susceptibility measurements. For EuFe 1− y Co y As 2 , the Eu-related antiferromagnetic (AFM) transition around 40 K is barely affected by Co doping, while the Fe-related spin density wave (SDW) transition temperature drops rapidly. Meanwhile, SC is induced by a trace amount of Co doping, with a highest transition temperature T c ∼28 K found in EuFe 0.9 Co 0.1 As 2 . For the Eu 0.9 Pr 0.1 Fe 1− y Co y As 2 series, the magnetism and superconductivity show similar evolutions upon Co doping, and the highest T c is enhanced to 30.6 K with an optimum doping level y ∼ 0.07. Our results shed light on the competition between SC and SDW with Co doping in the 112-type EuFeAs 2 system.