Superconductivity in Ru-substituted polycrystalline BaFe_2−xRu_xAs₂

The occurrence of bulk superconductivity at ∼22 K is reported in polycrystalline samples of BaFe_2−xRu_xAs₂ for nominal Ru content in the range of x=0.75–1.125. A systematic suppression of the spin-density-wave transition temperature (T_SDW) precedes the appearance of superconductivity in the system. A phase diagram is proposed based on the measured T_SDW and superconducting transition temperature (T_C) variations as a function of Ru composition. Band-structure calculations indicate introduction of electron carriers in the system upon Ru substitution. The calculated magnetic moment on Fe shows a minimum at x=1.0, suggesting that the suppression of the magnetic moment is associated with the emergence of superconductivity. Results of low-temperature and high-field Mössbauer measurements are presented. These indicate weakening of magnetic interaction with Ru substitution.