Superconductivity and upper fields in Na-doped iron arsenides Eu1−xNaxFe2As2

Abstract

In this paper, we report a systematic investigation of the crystal structure and superconducting properties of iron-based superconductors Eu1−xNaxFe2As2 (x = 0–0.5). X-ray diffraction patterns indicate that the compounds form the ThCr2Si2-type structure with space group I4/mmm. The systematic evolution of the lattice constant demonstrates that the Eu ions are successfully replaced by Na. The use of alkali metal substitution into the Eu site allows us to suppress the magnetic/structural phase transition in the parent compounds and superconductivity reaches as high as 35 K with a doping level of x = 0.5. In addition, single crystals of Eu1−xNaxFe2As2 (x = 0, 0.5) have been successfully synthesized using the self-flux method. The upper critical fields have been determined with the magnetic field along the ab-plane and thec-axis, yielding an anisotropy of 1.7. The high upper critical fields and the low superconducting anisotropy of the Na-doped EuFe2As2 compounds indicate a potential for applications such as the generation of high magnetic fields.