Superconductivity in SmFe1-xCoxAsO (x = 0.0 to 0.30)

TL;DR

This study investigates how cobalt doping in SmFeAsO affects its structural, magnetic, and superconducting properties, revealing optimal doping levels for superconductivity and the effects of disorder at higher doping concentrations.

Contribution

It provides detailed insights into the suppression of SDW and emergence of superconductivity due to Co doping in SmFeAsO, including the critical doping range and effects on magnetic properties.

Findings

Superconductivity appears at x=0.10, 0.15, 0.20 with transition temperatures 14K, 15.5K, 9K.

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

Superconductivity is absent at x=0.30 due to disorder and over-doping.

Abstract

We report synthesis, structural details and magnetization of SmFe1-xCoxAsO with x ranging from 0.0 to 0.30. 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 at around 140 K. 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 lower critical field as seen from magnetization measurements is below 200Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co i.e. x = 0.30. Clearly the Co substitution at Fe site in SmFe1-xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes non-superconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mobile electrons to the system and superconductivity appears, however direct substitution introduces simultaneous disorder in superconducting FeAs layer and thus superconductivity disappears for higher content of Co.