Appearance and disappearance of superconductivity with Fe site Co substitution in SmFe _1-xCo _xAsO (x = 0.0 to 1.0)

We report synthesis, structural details, and magnetization of SmFe _1-xCo _xAsO with x ranging from 0.0 to 1.0 at a close interval of 0.10. It is found that Co substitutes fully at the Fe site in SmFeAsO in an iso-structural lattice with a slightly compressed cell. The parent compound exhibited known spin density wave (SDW) character below 150 K. Successive doping of Co at the Fe site suppressed the SDW transition for x = 0.05, and later induced superconductivity for x = 0.10, 0.15, and 0.20, respectively, at 14, 15.5, and 9 K. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. For higher content of Co, i.e. x ≥ 0.30, superconductivity is not observed. Clearly, the Co substitution at the Fe site in SmFe _1-xCo _xAsO diminishes the Fe SDW character (x = 0.05), introduces bulk superconductivity for x from 0.10 to 0.20, and finally becomes a non-superconductor. The SmCoAsO also exhibits a secondary AFM-like transition below or around 50 K. The reported AFM ordering of Sm spins is seen from heat capacity C _p(T) at 4.5 K and the same remains invariant with Co doping in SmFe _1-xCo _xAsO. Further, the FM ordering of Co-spins (seen in magnetization measurements) is not evident in C _p(T) studies, suggesting weak correlations between ordered Co-spins in these systems.