Spin polarization of Ru in superconducting Ba(Fe${}_{0.795}$Ru${}_{0.205}$)${}_2$As${}_2$ studied by x-ray resonant magnetic scattering

We have employed the x-ray resonant magnetic scattering (XRMS) technique at the Ru $L_2$ edge of the Ba(Fe${}_{1-x}$Ru${}_x$)${}_2$As${}_2$ ($x=0.205$) superconductor. We show that pronounced resonance enhancements at the Ru $L_2$ edge are observed at the wave vector which is consistent with the antiferromagnetic propagation vector of the Fe in the undoped BaFe${}_2$As${}_2$. We also demonstrate that the XRMS signals at the Ru $L_2$ edge follow the magnetic ordering of the Fe with a long correlation length, ${\xi }_{ab}>2850\pm 400$ Å. Our experimental observation shows that the Ru is spin polarized in Ba(Fe${}_{1-x}$Ru${}_x$)${}_2$As${}_2$ compounds.

Figure 1

Temperature evolution of (a) [$H$, $H$, 0] scan through the (1, 1, 10) Bragg peak measured with off-resonance $E^{\prime }=8.901$ keV (${\lambda }^{\prime }=1.394$ Å) and (b) XRMS signal at the ($\frac{1}{2},-\frac{1}{2},3$) Bragg peak position with the fundamental component ($E=2.967$ keV and $\lambda =4.183$ Å) in Ba(Fe${}_{0.795}$Ru${}_{0.205}$)${}_2$As${}_2$. The data are shown with arbitrary offsets. The lines present the fitted curves using a Lorentzian-squared line shape.

Figure 2

(a) Temperature dependence of the orthorhombic distortion $\delta =\frac{a-b}{a+b}$ upon warming determined from fits to the $(1,1,10)$ Bragg peak. (b) The evolution of the integrated intensities (circles) and peak intensities (squares) of the $(\frac{1}{2},-\frac{1}{2},3)$ XRMS peak as a function of temperature during warming. The red bars indicate the structural/AFM transition temperatures, indicating that $T_S=T_N=43\pm 1$ K. The temperature-dependent XRMS signals and the orthorhombic distortion in the current work are compared with (c) the AFM ordering of the Fe moment and (d) the orthorhombic distortion observed in Ref. 19, respectively. Transition temperatures determined in Ref. 19 are marked with blue bars. The discrepancy in transition temperatures is likely due to the sample heating by the strong incident x-ray beam as described in the text.

Figure 3

Energy scan through the $(\frac{1}{2},-\frac{1}{2},3)$ XRMS peak (filled circles) and the energy-dependent absorption coefficient (open circles) calculated from the fluorescence spectrum measured at 45${}^{\circ }$ scattering angle around the Ru $L_2$ edge. The energy scan is corrected for absorption. Blue bars indicate positions of two resonant peaks. Lines are guides to eyes.