Combined effects of pressure and Ru substitution on BaFe2As2

Abstract

The $ab$ plane resistivity of Ba(Fe${}_{1\ensuremath{-}x}$Ru${}_{x}$)${}_{2}$As${}_{2}$ ($x=0.00$, 0.09, 0.16, 0.21, and 0.28) was studied under nearly hydrostatic pressures, up to 7.4 GPa, in order to explore the $T\ensuremath{-}P$ phase diagram and to compare the combined effects of isoelectronic Ru substitution and pressure. The parent compound BaFe${}_{2}$As${}_{2}$ exhibits a structural/magnetic phase transition near 134 K. At ambient pressure, progressively increasing Ru concentration suppresses this phase transition to lower temperatures at an approximate rate of $\ensuremath{\sim}$5 K/% Ru correlated with the emergence of superconductivity. By applying pressure to this system, a similar behavior is seen for each concentration: the structural/magnetic phase transition is further suppressed and superconductivity induced and ultimately, for larger $x$ Ru and $P$, suppressed. A detailed comparison of the $T\ensuremath{-}P$ phase diagrams for all Ru concentrations shows that 3 GPa of pressure is roughly equivalent to $10%$ Ru substitution. Furthermore, due to the sensitivity of Ba(Fe${}_{1\ensuremath{-}x}$Ru${}_{x}$)${}_{2}$As${}_{2}$ to pressure conditions, the melting of the liquid media, $4:6$ light mineral oil : $n$-pentane and $1:1$ isopentane : $n$-pentane, used in this study could be readily seen in the resistivity measurements. This feature was used to determine the freezing curves for these media and to infer their room temperature, hydrostatic limits: 3.5 and 6.5 GPa, respectively.