Large field-like torque in amorphous Ru2Sn3 originated from the intrinsic spin Hall effect

We investigated temperature dependent current driven spin-orbit torques in magnetron sputtered Ru$_2$Sn$_3$ (4 and 10 nm) /Co$_{20}$Fe$_{60}$B$_{20}$ (5 nm) layered structures with in-plane magnetic anisotropy. The room temperature damping-like and field-like spin torque efficiencies of the amorphous Ru$_2$Sn$_3$ films were extracted to be as large as 0.14 +- 0.008 and -0.2 +- 0.009, respectively, by utilizing the second harmonic Hall technique. The large field-like torque in the relatively thicker Ru$_2$Sn$_3$ (10 nm) thin film is unique compared to the traditional spin Hall materials interfaced with thick magnetic layers with in-plane magnetic anisotropy which typically have negligible field-like torques. Additionally, the observed room temperature field-like torque efficiency in Ru$_2$Sn$_3$ (10 nm)/CoFeB (5 nm) is up to three times larger than the damping-like torque (-0.20 +- 0.009 and 0.07 +- 0.012, respectively) and thirty times larger at 50 K (-0.29 +- 0.014 and 0.009 +- 0.017, respectively). The temperature dependence of the field-like torques are unique and show dominant contributions from the intrinsic spin Hall effect with intrinsic spin conductivity up to -240 +- 19 $\hbar$/2e ($\Omega$cm)$^{-1}$ while the damping-like torques show dominate contributions from the extrinsic spin Hall effects with sum of the skew scattering and side jump up to -175 +- 19 $\hbar$/2e ($\Omega$cm)$^{-1}$. Through macro-spin calculations, we found that including field-like torques on the order or larger than the damping-like torque can reduce the switching critical current and the switching time for a perpendicular ferromagnetic layer.