Temperature-pressure-composition phase diagram for Ba(Fe$_{1-x}$Ru$_{x})_{2}$As$_{2}$ (x$\le $0.285 and P$\le $84kbar)

BaFe$_{2}$As$_{2}$ shows a structural/magnetic (SM) phase transition near T$_{SM}$=134K, which is suppressed upon partial substitutions at the Ba (K), Fe (Cr, Mn, Co, Ni, Cu, Ru, Rh, Pd, Ir) or As (P) sites, and also by adding pressure (P), most times leading to the emergence of superconductivity (SC) at low T. Here, we report on the P-dependence of the electrical resistivity in under- to near-optimally doped Ba(Fe$_{1-x}$Ru$_{x})_{2}$As$_{2}$ (0$\le $x$\le $0.285) for P$\le $84kbar. Pressure suppresses the SM transition at a rate that increases with Ru content, e.g. for x=0.092, 0.161, and 0.210, dT$_{SM}$/dP $\sim $-0.2, -0.4, and -0.6K/kbar, respectively. Although the x=0.092 and x=0.161 compositions are not SC at P=0, SC is seen when T$_{SM}$ is sufficiently reduced by P. For x=0.161, T$_{c}$ at first increases to a maximum near 25K at $\sim $20kbar, after which it decreases at a rate of $\sim $-0.4K/kbar. Likewise, the T$_{c}$ values for the higher dopings peak $\sim $20kbar and decrease at higher P at similar rates. We find that the application of pressure on Ba(Fe$_{1-x}$Ru$_{x})_{2}$As$_{2}$ enhances T$_{c}$ beyond that which was achieved with only doping, seen before in Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$. -- Supported by U.S. DOE (DE-AC02-07CH11358), AFOSR-MURI (FA9550-09-1-0603), and NSF (DMR-0805335).