Energy-efficient spintronics through unconventional spin-orbit torque and voltage-controlled devices

As traditional computing and memory devices approach the quantum limit and face increasing challenges in further scaling, spintronics has emerged as a promising paradigm for next-generation platforms to meet the growing demand for computation and data storage. Among spintronic mechanisms, spin–orbit torque (SOT) has attracted significant attention for enabling ultrafast and reliable magnetization switching, as well as supporting in-memory computing architectures. However, the energy efficiency of current SOT-based devices remains suboptimal, which limits their adoption in practical applications. Furthermore, the requirement of an external magnetic field in conventional SOT materials poses an additional barrier for device integration. Recent studies have revealed that unconventional SOT can achieve much higher switching efficiency for magnets with perpendicular magnetic anisotropy. Nevertheless, material candidates have so far been largely restricted to two-dimensional systems, which are challenging to fabricate and integrate at scale. To address this limitation, we extend the material landscape to bulk systems and highlight Ni₄W as a representative example. Ni₄W has been experimentally demonstrated to exhibit large spin polarizations along the X, Y, and Z directions, and leveraging its out-of-plane spin component, field-free switching of a Ni₄W-based device has been successfully demonstrated. Additionally, the electric-field effect offers a promising pathway toward realizing low-power spintronic devices. However, achieving efficient voltage control remains a significant challenge. A new strategy for achieving highly efficient voltage-controlled magnetic anisotropy (VCMA) is based on work-function engineering of the SOT underlayer. By integrating a high work-function SOT underlayer to induce electron depletion at the CoFeB/MgO interface, VCMA coefficients exceeding 100 fJ V⁻¹ m⁻¹ have been achieved. We have also reviewed prior work showing that voltage-controlled exchange coupling can induce bipolar switching in superparamagnetic magnetic tunnel junctions, with power consumption estimated to be two orders of magnitude lower than that of conventional spin transfer torque control. These advancements pave the way for next-generation energy-efficient spintronic applications.