Observation of strong bulk damping-like spin-orbit torque in chemically disordered ferromagnetic single layers

TL;DR

This study reveals a surprisingly strong bulk damping-like spin-orbit torque in chemically disordered CoPt single layers, likely due to an intrinsic spin Hall effect, opening new possibilities for spintronic devices.

Contribution

First demonstration of strong bulk damping-like spin-orbit torque in chemically disordered ferromagnetic single layers, independent of spin sinks, linked to intrinsic spin Hall effect.

Findings

Strong { au}DL increases with CoPt thickness.

{ au}DL is insensitive to surface spin sinks.

Likely originates from a bulk spin Hall effect.

Abstract

Strong damping-like spin-orbit torque ({\tau}DL) has great potential for enabling ultrafast energy-efficient magnetic memories, oscillators, and logic. So far, the reported {\tau}DL exerted on a thin-film magnet must result from an externally generated spin current or from an internal non-equilibrium spin polarization in noncentrosymmetric GaMnAs single crystals. Here, we for the first time demonstrate a very strong, unexpected {\tau}DL from current flow within ferromagnetic single layers of chemically disordered, face-centered-cubic CoPt. We establish that the novel {\tau}DL is a bulk effect, with the strength per unit current density increasing monotonically with the CoPt thickness, and is insensitive to the presence or absence of spin sinks at the CoPt surfaces. This {\tau}DL most likely arises from a net transverse spin polarization associated with a strong spin Hall effect (SHE), while there is no detectable long-range asymmetry in the material. These results broaden the scope of spin-orbitronics and provide a novel avenue for developing single-layer-based spin-torque memory, oscillator, and logic technologies.