Prospect of Spin-Orbitronic Devices and Their Applications

Abstract

Science, engineering, and medicine ultimately demand fast information processing with ultra-low power consumption. The recently developed spin-orbit torque (SOT)-induced magnetization switching paradigm has been fueling opportunities for spin-orbitronic devices, i.e., enabling SOT memory and logic devices at sub-nano second and sub-picojoule regimes. Importantly, spin-orbitronic devices are intrinsic of nonvolatility, anti-radiation, unlimited endurance, excellent stability, and CMOS compatibility, toward emerging applications, e.g., processing in-memory, neuromorphic computing, probabilistic computing, and 3D magnetic random access memory. Nevertheless, the cutting-edge SOT-based devices and application remain at a premature stage owing to the lack of scalable methodology on the field-free SOT switching. Moreover, spin-orbitronics poises as an interdisciplinary field to be driven by goals of both fundamental discoveries and application innovations, to open fascinating new paths for basic research and new line of technologies. In this perspective, the specific challenges and opportunities are summarized to exert momentum on both research and eventual applications of spin-orbitronic devices.

Keywords: Applied Physics; Devices; Electronic Materials; Magnetic Property.

Graphical abstract

Figure 1

Comparisons between STT and SOT Schemes Schematic (A–C) STT and (D–F) SOT-associated device configuration, damping and damping-like torque under effective magnetic field, and corresponding precession dynamic trajectories. Note that the damping-like SOT only drives the magnetic moment m toward an in-plane direction, hence an orthogonal external in-plane magnetic field H_x is generally required to break the symmetry and results in a deterministic SOT-induced magnetization switching.

Figure 2

Schematics of Representative Emerging Spin-Orbitronic Device Applications

Figure 3

Strategies for Realizing Magnetic Field-free SOT Switching Representative symmetry breaking methods via generation or engineering of either (A) magnetic field H_x (Fukami et al., 2016; Cao et al., 2019), (B) magnetic anisotropy (Yu et al., 2014), or (C and D) spin-orbit current ${\mathit{j}}_{\mathit{S}}$ (Cai et al., 2017; Cao et al., 2020). Copyrights 2014, 2017, Springer Nature; Copyrights 2019, 2020, John Wiley & Sons, Inc.

Figure 4

A Proposed 3D SOT-MRAM Schematic of proposed single two-terminal SOT-MTJ cell (A) and the corresponding integrated 3D SOT-MRAM architecture (B). Writing and reading currents can be addressed to a specific MTJ cell by controlling the transistor switches and selectors. FL, free layer; RL, reference layer; SEL, selector; TE, top electrode.

Figure 5

Devices for Programmable Spin-orbit Logics Representative reprinted works reported on, or potentially capable of, demonstrating programmable spin-orbit logics based on various device approaches, e.g., (A) reconfigurable SOT switching of the PMA-FM layer in a “T-type” magnetically coupled structure realized by tuning the magnetization direction of the assistant in-plane FM layer via in-plane configured SOTs by applying orthogonal electrical currents (Wang et al., 2018b). (B) VCMA control of the PMA and thereby the driving current intensity of the SOT switching (Baek et al., 2018b). (C) Tuning the polarity of current-induced spin accumulation by modulating the oxygen ions in a Pt/Co/GdO_x structure by voltage gating, the interfacial chemistry of which results in an interplay between the interfacial torques and the spin Hall current from Pt, and determines the sense of the SOT-induced magnetization switching (Mishra et al., 2019). (D) External magnetic field-free reconfigurable SOT switching of Pt/CoNiCo/Pt obtained by electrically controlling the nonvolatile polarity of the ferroelectric PMN-PT substrate, where sufficient gradient in spin-orbit current is produced, and the direction of which determines the SOT switching sense to be clockwise or anticlockwise (Cai et al., 2017). (E) MESO devices involving the magnetoelectric effect and the charge-to-spin interconversions via spin filter and spin-obit effects (Manipatruni et al., 2019). (F) Reconfigurable and cascadable SOT-induced magnetic domain-wall logics by exploiting the invertible chiral coupling between neighboring magnetic domains (Luo et al., 2020). Copyright 2018, John Wiley & Sons, Ltd; Copyrights 2017, 2019, 2020 Springer Nature.

Figure 6

Representative Reprinted Works Reported on Spin-Orbitronics in Exotic Magnetic Materials beyond the Ferromagnets (A) Electric switching of antiferromagnet. Unlike conventional SOTs generated in HM/FM bilayers, the opposite signs of spin polarization at individual spin sublattices give staggered SOTs in a single CuMnAs layer (Wadley et al., 2016). (B) Generation and motion of magnetic skyrmions by spatially divergent SOTs (Jiang et al., 2015). (C) Electrical switching of a Fe₃GeTe₂ van der Waals material via SOTs generated from the capping Pt layer (Wang et al., 2019a). (D) Magnetic domain wall motions as well as magnetization switching induced by the torques mediated by spin waves (magnons), the phase and magnitude of which can also be tuned by the domain walls mutually in a nonvolatile manner (Han et al., 2019; Wang et al., 2019b). Copyrights 2015, 2016, 2019, 2019 AAAS.