  The spin currents generated by spin-orbit coupling (SOC) in the nonmagnetic
metal layer or at the interface with broken inversion symmetry are of
particular interest and importance. Here, we have explored the spin current
generation mechanisms through the spin-orbit torques (SOTs) measurements in the
Ru/Fe heterostructures with weak perpendicular magnetic anisotropy (PMA).
Although the spin Hall angle (SHA) of Ru is smaller than that in Pt, Ta or W,
reversible SOT in Ru/Fe heterostructures can still be realized. Through
non-adiabatic harmonic Hall voltage measurements and macrospin simulation, the
effective SHA in Ru/Fe heterostructures is compared with Pt. Moreover, we also
explore that the spin current driven by interface strongly depends on the
electrical conductivities. Our results suggest a new method for efficiently
generating finite spin currents in ferromagnet/nonmagnetic metal bilayers,
which establishes new opportunities for fundamental study of spin dynamics and
transport in ferromagnetic systems.
