“…This observed dependence of the switching sense on the location of the laser track could be exploited in integrated circuits with complementary spin logic and/or memory units. [ 28,29 ]…”
For more than a decade, the electrical switching of ferromagnets (FMs) with perpendicular magnetic anisotropy (PMA), using spin-transfer torque (STT) and more recently spin-orbit torque (SOT), has underpinned the development of fast, low-power-consumption, and high-density spintronic devices. [1][2][3][4][5] In general, both the STT-and the SOT-induced switching of a FM layer require an injection of out-ofplane spin current from nearby layers. [6][7][8] For STT-induced FM switching, particularly, a spin-polarized current is generated in a magnetic tunneling junction structure when a charge current flows perpendicularly through the stacks, where another FM layer acts as a spin polarizer. [9] Thus, device instability issues arise since the tunneling barrier layer between the two FM layers is required to transmit large switching currents.The SOT-induced FM switching, on the other hand, circumvents this problem by using an in-plane switching current. Conventionally, a stack structure consisting of a strong spin-orbit coupling (SOC) layer and a FM layer is used, where an in-plane charge current gives rise to an out-of-plane pure spin current due to spin Hall effect in the SOC layer and/or Rashba effect from the perpendicular interfacial inversion asymmetry. [10][11][12][13] The resulting SOT-induced effective magnetic field is in-plane, hence an additional orthogonal in-plane magnetic field is required to realize deterministic switching of a PMA-FM. To date, several approaches for field-free SOT-induced PMA-FM switching have been proposed and demonstrated, such as switching using a polarized ferroelectric substrate induced in-plane spin current gradient, [14][15][16] a wedge oxide capping layer, [17] a tilted PMA layer, [18] a stack with coherent in-plane exchange field, [19][20][21][22][23] an interplay of SOT and STT, [24,25] an inplane-FM/normal metal/PMA-FM trilayer, [26] and a particular low symmetric WTe 2 semimetal. [27] However, the concomitant complexities of these approaches highlight the inherent limitation of the conventional SOT scheme utilizing external outof-plane spin current injection in a perpendicular asymmetric structure.Here, we demonstrate magnetic field-free deterministic current-induced magnetization switching in a PMA Pt/Co/ Pt trilayer subjected to local laser annealing. Without external magnetic field, the direction of current-induced magnetization switching is found to depend on the relative location and Current-induced magnetization switching by spin-orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin-orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, deterministic current-induced SOT full magnetization switching by lateral spin-orbit torque in zero external magnetic field is reported. The Pt/Co/Pt magn...
“…This observed dependence of the switching sense on the location of the laser track could be exploited in integrated circuits with complementary spin logic and/or memory units. [ 28,29 ]…”
For more than a decade, the electrical switching of ferromagnets (FMs) with perpendicular magnetic anisotropy (PMA), using spin-transfer torque (STT) and more recently spin-orbit torque (SOT), has underpinned the development of fast, low-power-consumption, and high-density spintronic devices. [1][2][3][4][5] In general, both the STT-and the SOT-induced switching of a FM layer require an injection of out-ofplane spin current from nearby layers. [6][7][8] For STT-induced FM switching, particularly, a spin-polarized current is generated in a magnetic tunneling junction structure when a charge current flows perpendicularly through the stacks, where another FM layer acts as a spin polarizer. [9] Thus, device instability issues arise since the tunneling barrier layer between the two FM layers is required to transmit large switching currents.The SOT-induced FM switching, on the other hand, circumvents this problem by using an in-plane switching current. Conventionally, a stack structure consisting of a strong spin-orbit coupling (SOC) layer and a FM layer is used, where an in-plane charge current gives rise to an out-of-plane pure spin current due to spin Hall effect in the SOC layer and/or Rashba effect from the perpendicular interfacial inversion asymmetry. [10][11][12][13] The resulting SOT-induced effective magnetic field is in-plane, hence an additional orthogonal in-plane magnetic field is required to realize deterministic switching of a PMA-FM. To date, several approaches for field-free SOT-induced PMA-FM switching have been proposed and demonstrated, such as switching using a polarized ferroelectric substrate induced in-plane spin current gradient, [14][15][16] a wedge oxide capping layer, [17] a tilted PMA layer, [18] a stack with coherent in-plane exchange field, [19][20][21][22][23] an interplay of SOT and STT, [24,25] an inplane-FM/normal metal/PMA-FM trilayer, [26] and a particular low symmetric WTe 2 semimetal. [27] However, the concomitant complexities of these approaches highlight the inherent limitation of the conventional SOT scheme utilizing external outof-plane spin current injection in a perpendicular asymmetric structure.Here, we demonstrate magnetic field-free deterministic current-induced magnetization switching in a PMA Pt/Co/ Pt trilayer subjected to local laser annealing. Without external magnetic field, the direction of current-induced magnetization switching is found to depend on the relative location and Current-induced magnetization switching by spin-orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin-orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, deterministic current-induced SOT full magnetization switching by lateral spin-orbit torque in zero external magnetic field is reported. The Pt/Co/Pt magn...
“…However, only a few discrete resistance states were observed in these experiments, due to the fact that DW can only be pinned at a few locations. Spin–orbit torque (SOT), generated by current injection in heavy metal (HM)/ferromagnet (FM) bilayers, has attracted great attention as an alternative method to switch the magnetization and to move DW or magnetic skyrmion in an FM layer, instead of or cooperating with magnetic field, STT, and electric field . Very recently, Fukami et al demonstrated analog memristive behavior induced by SOT in a PtMn/[Co/Ni] antiferromagnetic (AFM)/FM bilayer system by performing R – I sweeps .…”
Memristors, demonstrated by solid-state devices with continuously tunable resistance, [1][2][3][4][5][6][7] have emerged as a new paradigm for self-adaptive networks that require synapse-like functions (artificial synapse, for example). Spin-based memristors offer advantages over other types of memristors because of their significant endurance and high energy efficiency. [8,9] Yet, it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. [10] Here, a memristive device based upon Ta/CoFeB/MgO heterostructures is demonstrated, which are commonly used in out-of-plane magnetized magnetic tunnel junctions. [11] To achieve the memristive function, a domain wall (DW) is driven back and forth in a continuous manner in the CoFeB layer by applying in-plane positive or negative current pulses along the Ta layer, utilizing the spin-orbit torque (SOT) that the current exerts on the CoFeB magnetization. [12][13][14][15][16][17] Hence, Memristors, demonstrated by solid-state devices with continuously tunable resistance, have emerged as a new paradigm for self-adaptive networks that require synapse-like functions (artificial synapse, for example). Spin-based memristors offer advantages over other types of memristors because of their significant endurance and high energy efficiency. Yet it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. Here, a memristive device based upon Ta/CoFeB/MgO heterostructures is demonstrated, which are commonly used in out-of-plane magnetized magnetic tunnel junctions (MTJ). To achieve the memristive function, a domain wall (DW) is driven back and forth in a continuous manner in the CoFeB layer by applying in-plane positive or negative current pulses along the Ta layer, utilizing the spin-orbit torque (SOT) that the current exerts on the CoFeB magnetization. Hence, the magnetization and consequently the anomalous Hall effect (AHE) resistance are modulated in an analog manner, being controlled by the pulsed current characteristics including amplitude, duration, and repetition number. The quasi-continuous AHE resistance variation is explained by the SOT-induced DW creep motion. These results pave the way for developing SOT-based energy-efficient neuromorphic systems.
“…One basic idea is to adjust the interlayer coupling field direction by magnetically or electrically pre-magnetizing the in-plane FM pinning layer within the “T-type” magnetically coupled HM/PMA-FM free layer/spacer layer/in-plane FM pinning layer stacks ( Sheng et al., 2018a ; Wan et al., 2017 ; Wang et al., 2018b ), as shown in Figure 5 A. Typically, the voltage-controlled magnetic anisotropy (VCMA) in the FM ( Lee et al., 2016 ; Baek et al., 2018b ; Wang, 2018 ; Grimaldi et al., 2020 ) (i.e., Figure 5 B), as well as the gate-voltage tunable spin-orbit current from either a metal oxide ( Mishra et al., 2019 ) as illustrated in Figure 5 C, semiconductor ( Chen et al., 2018b ), a van der Waals crystal ( Benitez et al., 2020 ), or a topological insulator ( Fan et al., 2016 ), provides a class of powerful electrical manipulation methods for programmable spin-orbit logics. Besides, introducing other multiferroic behaviors beyond the ferromagnetism, such as the ferroelectric/HM/FM heterostructure ( Cai et al., 2017 ; Belopolski et al., 2019 ; Filianina et al., 2020 ; Noël et al., 2020 ; Fang et al., 2020 ) (see Figure 5 D) and the novel proposal of magnetoelectric spin-orbit logics (MESO, see Figure 5 E), can also bring additional nonvolatile freedoms for realizing all electrically programmable functionalities ( Manipatruni et al., 2019 ).…”
Section: The Future Opportunitiesmentioning
confidence: 99%
“… 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 ).…”
Summary
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.
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