Spin-orbit torque generated by amorphous Fe$_{x}$Si$_{1-x}$

TL;DR

This study demonstrates room-temperature spin-orbit torque in amorphous Fe$_{x}$Si$_{1-x}$ / cobalt bilayers with efficiency comparable to heavy metals, revealing new physics and potential for CMOS-compatible spintronics.

Contribution

It reports the observation of significant spin-orbit torque in amorphous Fe$_{x}$Si$_{1-x}$, a low-Z, silicon-based material, challenging conventional theories and expanding material options for spintronics.

Findings

Spin torque efficiency of about 3% in Fe$_{x}$Si$_{1-x}$/Co bilayers.

Observation of spin-orbit torque in a low-Z, amorphous material.

Potential for CMOS-compatible spintronic devices.

Abstract

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.