Persistent Magnetism in Silver-doped BaFe2As2 Crystals

We investigate the thermodynamic and transport properties of silver-substituted BaFe2As2 (122) crystals, up to ~4.5%. Similar to other transition-metal substitutions in 122, Ag diminishes the antiferromagnetic (TN) and structural (TS) transition temperatures, but unlike other electron-doped 122s, TN and TS coincide without splitting. Although magnetism drops precipitously to TN = 84 K at doping x = 0.029, it only weakly changes above this x, settling at TN = 80 K at x = 0.045. Compared to this persistent magnetism in Ag-122, doping other group 11 elements of either Cu or Au in 122 diminished TN and induced superconductivity near TC = 2 K at x = 0.044 or 0.031, respectively. Ag-122 crystals show reflective surfaces with surprising thicker cross sections for x >= 0.019, the appearance that is in contrast to the typical thin stacked layered feature seen in all other flux-grown x122 and lower Ag-122. This physical trait may be a manifest of intrinsic weak changes in c-lattice and TN. Our theoretical calculations suggest that Ag doping produces strong electronic scattering and yet a relatively small disruption of the magnetic state, both of which preclude superconductivity in this system.

PDF Abstract