Physical and magnetic properties of $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$ single crystals

Single crystals of $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$, $x<0.37$, have been grown and characterized by structural, magnetic, and transport measurements. These measurements show that the structural/magnetic phase transition found in pure ${\text{BaFe}}_2{\text{As}}_2$ at 134 K is suppressed monotonically by Ru doping but, unlike doping with $TM=\text{Co}$, Ni, Cu, Rh, or Pd, the coupled transition seen in the parent compound does not detectably split into two separate ones. Superconductivity is stabilized at low temperatures for $x>0.2$ and continues through the highest doping levels we report. The superconducting region is domelike, with maximum $T_c\left(\sim 16.5\text{K}\right)$ found around $x\sim 0.29$. A phase diagram of temperature versus doping, based on electrical transport and magnetization measurements, has been constructed and compared to those of the $\text{Ba}{\left({\text{Fe}}_{1-x}T{M}_x\right)}_2{\text{As}}_2$ ($TM=\text{Co}$, Ni, Rh, and Pd) series as well as to the temperature-pressure phase diagram for pure ${\text{BaFe}}_2{\text{As}}_2$. Suppression of the structural/magnetic phase transition as well as the appearance of superconductivity is much more gradual in Ru doping, as compared to Co, Ni, Rh, and Pd doping, and appears to have more in common with ${\text{BaFe}}_2{\text{As}}_2$ tuned with pressure; by plotting $T_S/T_m$ and $T_c$ as a function of changes in unit-cell dimensions, we find that changes in the $c/a$ ratio, rather than changes in $c$, $a$, or $V$, unify the $T\left(p\right)$ and $T\left(x\right)$ phase diagrams for ${\text{BaFe}}_2{\text{As}}_2$ and $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$, respectively.

Figure 1

Experimentally determined Ru concentration, $x_{\text{WDS}}$, vs nominal Ru concentration. Error bars are $\pm 2\sigma$ (values from Table ).

Figure 2

Powder x-ray pattern for $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$, $x=0.073$, with Si standard. Open symbols are measured data, closed ones are fit, the line shows the difference. $\times$, $\mid$, and $+$ symbols are calculated peak positions for Si, FeAs, and the sample.

Figure 3

(Color online) Lattice parameters for $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$, compared to ${\text{BaFe}}_2{\text{As}}_2$, for which $a_0=3.96\text{Å}$, $c_0=13.0\text{Å}$, and $V_0=204{\text{Å}}^3$. The slopes are $a/a_0:\left(3.7\pm 0.1\right)\times {10}^{-4}/\text{Ru}\text{atom}$, $c/c_0:\left(-4.9\pm 0.1\right)\times {10}^{-4}/\text{Ru}\text{atom}$, and $V/V_0:\left(2.4\pm 0.2\right)\times {10}^{-4}/\text{Ru}\text{atom}$. The trend lines are determined by a least-squares fit. The error in the slope is the standard error from this fit.

Figure 4

(Color online) Temperature-dependent resistance, normalized to the room-temperature value, for select $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$ doping levels. Inset shows low-temperature behavior.

Figure 5

(Color online) (a) Temperature-dependent magnetization, scaled by applied field $H=70\text{kOe}$, for $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$. (b) Low-temperature, low-field, zero-field cooled and field-cooled magnetization for several superconducting members of the $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$ family. $H\perp c$ for all data sets. The relatively large, low temperature, diamagnetic shielding in the zero-field cooled measurements approaches that found for Co, Ni, Rh, and Pd doping (Refs. 6, 10, 14, 17).

Figure 6

(Color online) (a) Magnetization and (b) normalized resistance, along with derivatives, for $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2\left(x=0.073\right)$. Vertical arrows show the criteria for determination of the transition temperature. (c) shows normalized resistance derivative data for Co doping $\left(x=0.024\right)$ and Rh doping $\left(x=0.012\right)$ with similar transition temperatures.

Figure 7

(Color online) (a) Magnetization and (b) normalized resistance, along with derivatives, for $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2\left(x=0.16\right)$. Vertical arrows show the criteria for determination of the transition temperature. (c) shows normalized resistance derivative data for Co doping $\left(x=0.038\right)$ and Rh doping $\left(x=0.039\right)$ with similar transition temperatures.

Figure 8

(Color online) $x$ dependent phase diagram, showing $T$ for salient features in $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$.

Figure 9

(Color online) Comparison of Ru-doping phase diagram with that of the parent ${\text{BaFe}}_2{\text{As}}_2$ compound under applied pressure.

Figure 10

(Color online) Phase diagrams of $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ru}}_x\right)}_2{\text{As}}_2$ and of parent ${\text{BaFe}}_2{\text{As}}_2$ under pressure, scaled by lattice parameters. (a) is scaled by $\Delta c/c_0$. (b) is scaled by $\Delta \left(c/c_0\right)/\left(a/a_0\right)$.