Absence of superconductivity in hole-doped BaFe2−xCrxAs2 single crystals

We investigate the physical properties and electronic structure upon Cr doping in the iron arsenide layers of BaFe2As2. This form of hole doping leads to suppression of the magnetic/structural phase transition in BaFe2−xCrxAs2 for x>0, but does not lead to superconductivity. For x≤0.75 values, temperature dependence of the resistivity, specific heat, magnetic susceptibility, Hall coefficient, and single-crystal x-ray diffraction data are presented. The resulting phase diagram is suggestive that superconductivity does not derive simply from the suppression of the structural/magnetic transitions. The materials show signatures of approaching a ferromagnetic state for x as little as 0.36 by an enhanced Wilson ratio. Such results reflect renormalization due to spin fluctuations and they are supported by density-functional supercell calculations for slightly higher doping level of x=1. Calculations show a strong interplay between magnetic ordering and chemical ordering of Fe and Cr, with a ferromagnetic ground state.