Appearance and disappearance of superconductivity with Fe site Co substitution in SmFe1-xCoxAsO (x = 0.0 to 1.0)

TL;DR

This study explores how substituting Co for Fe in SmFeAsO affects its magnetic and superconducting properties, revealing that Co doping suppresses SDW order and induces superconductivity within a specific doping range.

Contribution

It provides detailed insights into the evolution of magnetic and superconducting phases with Co doping in SmFeAsO, including the suppression of SDW and the emergence of bulk superconductivity.

Findings

Superconductivity appears at x=0.10-0.20 with T_c up to 15.5K.

SDW order is suppressed with Co doping, disappearing at x=0.05.

Superconductivity is absent for x ≥ 0.30.

Abstract

We report synthesis, structural details and magnetization of SmFe1-xCoxAsO with x ranging from 0.0 to 1.0 at close interval of 0.10. It is found that Co substitutes fully at Fe site in SmFeAsO in an iso-structural lattice with slightly compressed cell. The parent compound exhibited known spin density wave (SDW) character below 150K. Successive doping of Co at 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 9K. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. For higher content of Co i.e. x \geq 0.30, superconductivity is not observed. Clearly the Co substitution at Fe site in SmFe1-xCoxAsO 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 at below around 50 K. The reported AFM ordering of Sm spins is seen from heat capacity Cp(T) at 4.5 K and the same remains invariant with Co doping in SmFe1-xCoxAsO. Further the FM ordering of Co-spins (seen in magnetization measurements) is not evident in Cp(T) studies, suggesting weak correlations between ordered Co-spins in these systems.