Spin-Orbit Torque Phenomena in Magnetic Heterostructures

Spin-orbit torques (SOTs) arise when an electrical current flowing through a heavy metal or exotic magnetic material generates a non-equilibrium spin accumulation at an adjacent ferromagnetic layer. This spin accumulation can exert a torque on the local magnetisation, enabling ultrafast and energy‐efficient switching of magnetic bits without applied magnetic fields. In magnetic heterostructures—engineered stacks of heavy metals, ferromagnets, antiferromagnets and insulating spacers—spin Hall and interfacial Rashba–Edelstein effects convert charge current to spin current, while Dzyaloshinskii–Moriya interactions govern chiral domain‐wall textures. Recent advances exploit noncollinear antiferromagnets and topological spin textures to generate out‐of‐plane spin polarisation, overcoming the in‐plane‐only limit of conventional SOT. Synthetic antiferromagnets provide tunable net magnetisation and enhanced thermal stability. The ability to tailor interfacial crystallinity, control Dzyaloshinskii–Moriya strength and exploit orbital degrees of freedom has led to field‐free switching schemes and record‐low switching currents. This body of work underpins potential applications in next‐generation magnetic random access memory (MRAM), neuromorphic devices and low‐power logic.

Research from Nature Portfolio

Recent studies have revealed that noncollinear antiferromagnets can serve as highly anisotropic spin sources. In one example, a face‐centred cubic antiferromagnet was shown to generate a spin current whose magnitude and polarisation depend strongly on the in‐plane direction of the driving current, enabling field‐free perpendicular switching of an adjacent ferromagnet at record‐low power. In synthetic antiferromagnet stacks with perpendicular anisotropy, researchers have demonstrated that by engineering the interfacial crystallinity with heavy metals, the Dzyaloshinskii–Moriya interaction can be tuned to favour Néel‐type domain walls, allowing deterministic, field‐free SOT switching in simple wedged structures. Complementary work in topological antiferromagnets has identified a giant out‐of‐plane field‐like torque linked to the magnetic spin Hall effect, with its magnitude controlled by the antiferromagnetic order parameter. These breakthroughs point to universal strategies for achieving deterministic, low‐power magnetisation control via SOT in complex magnetic heterostructures.

Spin-Orbit Torque Phenomena in Magnetic Heterostructures publication trend

The graph below shows the total number of articles in spin-orbit torque phenomena in magnetic heterostructures across all publications each year (not limited to Nature Index journals).

Technical terms

Spin-orbit torque (SOT): Torque on a magnetic layer arising from a non-equilibrium spin accumulation generated by spin–orbit coupling in adjacent materials.

Spin Hall effect: Conversion of a longitudinal charge current into a transverse spin current in materials with strong spin–orbit coupling.

Rashba–Edelstein effect: Interfacial spin polarisation induced by broken inversion symmetry under an applied electric field.

Dzyaloshinskii–Moriya interaction (DMI): Chiral exchange interaction favouring noncollinear spin textures and stabilising Néel‐type domain walls.

Synthetic antiferromagnet (SAF): Engineered multilayer stack of ferromagnetic layers coupled antiferromagnetically to yield low net magnetisation and high stability.

Orbital-transfer torque (OTT): Torque generated by transfer of orbital angular momentum from a current-induced orbital polarisation to an adjacent ferromagnet.

Van der Waals heterostructure: Stack of atomically thin materials bonded by van der Waals forces, offering pristine interfaces and tunable electronic properties.

References

1. Anomalous spin current anisotropy in a noncollinear antiferromagnet. Nature Communications (2023).
2. Reducing Dzyaloshinskii-Moriya interaction and field-free spin-orbit torque switching in synthetic antiferromagnets. Nature Communications (2021).
3. Giant field-like torque by the out-of-plane magnetic spin Hall effect in a topological antiferromagnet. Nature Communications (2021).
4. Room-temperature orbit-transfer torque enabling van der Waals magnetoresistive memories. Science Bulletin (2023).
5. Observation of charge to spin conversion in Weyl semimetal WTe2 at room temperature. Physical Review Research (2020).