Magnetic and superconducting phase diagram of Eu(Fe1−xNix)As2

Abstract

We report the Ni-doping effect on magnetism and superconductivity (SC) in an Eu-containing 112-type system Eu(Fe1−xNix)As2 (0≤x≤0.15) by the measurements of resistivity, magnetization, and specific heat. The undoped EuFeAs2 undergoes a spin-density-wave (SDW) transition at TSDW∼105K in the Fe sublattice and a magnetic ordering at Tm∼40K in the Eu sublattice. Complex Eu-spin magnetism is manifested by a spin-glass reentrance at TSG∼15K and an additional spin reorientation at TSR∼7K. With Ni doping, the SDW order is rapidly suppressed, and SC emerges in the Ni-doping range of 0.01 ≤x≤ 0.1 where a maximum of the superconducting transition temperature Tcmax=17.6K shows up at x=0.04. On the other hand, Tm decreases very slowly, yet TSG and TSR hardly change with the Ni doping. The phase diagram has been established, which suggests a very weak coupling between SC and Eu spins. The complex Eu-spin magnetism is discussed in terms of the Ruderman-Kittel-Kasuya-Yosida interactions mediated by the conduction electrons from both layers of FeAs and As surrounding Eu2+ ions.

Source-reported materials — not catalogue approval

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