The magnetism for NN AFM ground state in Fe-based superconductor: Sr1−xKxFe2As2

The crystal structure, magnetism properties, and density of states for FeAs layered compound SrFe2As2 have been investigated by using the density functional theory (DFT) method. The magnetism under a checkerboard nearest neighbor anti-ferromagnetic (NN AFM) and ferromagnetic (FM) order ground-state have been analyzed with substitution for Sr with K ion in Sr1−xKxFe2As2. The results indicate that the distortion of FeAs tetrahedrons is sensitive to the electron doping concentration. The system magnetism was suppressed by K doping in NN-AFM ground state instead of FM. The density of states at Fermi level N(EF)N(EF) under NN AFM ground state would be regarded as a driving force for the increased TcTc of Sr1−xKxFe2As2 system as observed experimentally. Our calculation reflects that NN AFM type spin fluctuation may still exist in the Sr1−xKxFe2As2 system and it may be an origin of strong spin fluctuation in this system besides the spin density wave (SDW) states.

► FeAs4 tetrahedrons of Sr1−xKxFe2As2 are sensitive to the electron doping.
► Magnetism was suppressed in the NN-AFM state of Sr1−xKxFe2As2 system.
► N(EF)N(EF) under NN AFM was regarded as a driving force for the increased TcTc.
► NN AFM type spin fluctuation may still exist in Sr1−xKxFe2As2 system.