The magnetism in ${\text{SrFe}}_2{\text{As}}_2$ can be suppressed by electron doping through a small substitution of Fe by Co or Ni, giving way to superconductivity. We demonstrate that a massive substitution of Fe by isovalent ruthenium similarly suppresses the magnetic ordering in ${\text{SrFe}}_{2-x}{\text{Ru}}_x{\text{As}}_2$ and leads to bulk superconductivity for $0.6\le x\le 0.8$. Magnetization, electrical resistivity, and specific-heat data show $T_c$ up to $\approx 20\text{K}$. Detailed structural investigations reveal a strong decrease in the lattice parameter ratio $c/a$ with increasing $x$. Density functional theory band-structure calculations are in line with the observation that the magnetic order in ${\text{SrFe}}_{2-x}{\text{Ru}}_x{\text{As}}_2$ is only destabilized for large $x$.

• Received 12 March 2009

DOI:https://doi.org/10.1103/PhysRevB.79.214516