Effect of Co doping and hydrostatic pressure on SrFe2As2

Abstract

We report a pressure study on electron doped SrFe${}_{2-x}$Co${}_x$As${}_2$ by electrical-resistivity ($\rho$) and magnetic-susceptibility ($\chi$) experiments. Application of either external pressure or Co substitution rapidly suppresses the spin-density wave ordering of the Fe moments and induces superconductivity in SrFe${}_2$As${}_2$. At $x=0.2$ the broad superconducting (SC) dome in the $T-p$ phase diagram exhibits its maximum $T_{c,\max }=20$ K at a pressure of only $p_{\max }\approx 0.75$ GPa. In SrFe${}_{1.5}$Co${}_{0.5}$As${}_2$ no superconductivity is observed anymore up to 2.8 GPa. Upon increasing the Co concentration the maximum of the SC dome shifts toward lower pressure accompanied by a decrease in the value of $T_{c,\max }$. Even though, superconductivity is induced by both tuning methods, Co substitution leads to a much more robust SC state. Our study evidences that in SrFe${}_{2-x}$Co${}_x$As${}_2$ both, the effect of pressure and Co-substitution, have to be considered in order to understand the SC phase-diagram and further attests the close relationship of SrFe${}_2$As${}_2$ and its sister compound BaFe${}_2$As${}_2$.

6 pages, 6 figures

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