  While tremendous work has gone into spin-orbit torque and spin current
generation, charge-to-spin conversion efficiency remains weak in silicon to
date, generally stemming from the low spin-orbit coupling (low atomic number,
Z) and lack of bulk lattice inversion symmetry breaking. Here we report the
observation of spin-orbit torque in an amorphous, non-ferromagnetic
Fe$_{x}$Si$_{1-x}$ / cobalt bilayer at room temperature, using spin torque
ferromagnetic resonance and harmonic Hall measurements. Both techniques provide
a minimum spin torque efficiency of about 3 %, comparable to prototypical heavy
metals such as Pt or Ta. According to the conventional theory of the spin Hall
effect, a spin current in an amorphous material is not expected to have any
substantial contribution from the electronic bandstructure. This, combined with
the fact that Fe$_{x}$Si$_{1-x}$ does not contain any high-Z element, paves a
new avenue for understanding the underlying physics of spin-orbit interaction
and opens up a new class of material systems - silicides - that is directly
compatible with complementary metal-oxide-semiconductor (CMOS) processes for
integrated spintronics applications.
