Unveiling the mechanism of bulk spin-orbit torques within chemically disordered Fe${}_x$Pt${}_{1-x}$ single layers

Abstract

Recent discovery of spin-orbit torques (SOTs) within magnetic single-layers has attracted attention in the field of spintronics. However, it has remained elusive as to how to understand and how to tune the SOTs. Here, utilizing the single layers of chemically disordered Fe${}_x$Pt${}_{1-x}$, we unveil the mechanism of the "unexpected" bulk SOTs by studying their dependence on the introduction of a controlled vertical composition gradient and on temperature. We find that the bulk damping like SOT arises from an imbalanced internal spin current that is transversely polarized and independent of the magnetization orientation. The torque can be strong only in the presence of a vertical composition gradient and the SOT efficiency per electric field is insensitive to temperature but changes sign upon reversal of the orientation of the composition gradient, which are in analogue to behaviors of the strain. From these characteristics we conclude that the imbalanced internal spin current originates from a bulk spin Hall effect and that the associated inversion asymmetry that allows for a non-zero net torque is most likely a strain non-uniformity induced by the composition gradient. The fieldlike SOT is a relatively small bulk effect compared to the dampinglike SOT. This work points to the possibility of developing low-power single-layer SOT devices by strain engineering.

Advanced Functional Materials (in production)

References in corpus (8)

• Single-shot dynamics of spin-orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions
• Evolution of the spin Hall effect in Pt nanowires: Size and temperature effects
• Strong damping-like spin-orbit torque and tunable Dzyaloshinskii-Moriya interaction generated by low-resistivity Pd${}_{1-x}$Pt${}_x$ alloys
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• Current-induced magnetization switching in CoTb amorphous single layer
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Cited by in corpus (10)

• Maximizing Spin-Orbit Torque Generated by the Spin Hall Effect of Pt
• Switching of Perpendicular Magnetization by Spin-Orbit Torque
• Quantifying the Dzyaloshinskii-Moriya Interaction Induced by the Bulk Magnetic Asymmetry
• From Early Theories of Dzyaloshinskii-Moriya Interactions in Metallic Systems to Today's Novel Roads
• Gigantic Anisotropy of Self-Induced Spin-Orbit Torque in Weyl Ferromagnet Co2MnGa
• Current-induced perpendicular effective magnetic field in magnetic heterostructures
• Anomalous sign inversion of spin-orbit torque in ferromagnetic/nonmagnetic bilayer systems due to self-induced spin-orbit torque
• Vertically Graded Fe-Ni Alloys with Low Damping and a Sizeable Spin-Orbit Torque
• Self-induced spin pumping and inverse spin Hall effect in single FePt thin films
• Negligible current-induced torque from the bulk and interface of Al