Deterministic Magnetization Switching Using Lateral Spin–Orbit Torque

Abstract

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...

Observation of Strong Bulk Damping‐Like Spin‐Orbit Torque in Chemically Disordered Ferromagnetic Single Layers

“…The novel bulk τ DL we demonstrate here may also provide a possible interpretation for the absence of τ DL in thin L 1 0 ‐FePt single crystal, [ 28 ] the presence of self‐induced switching in very thick L 1 0 ‐FePt single crystal, [ 29 ] and the presence of a nonzero τ DL in Co/Pd multilayer nanowires [ 30 ] and in a 15 nm‐thick nearly compensated ferrimagnetic Tb‐Co film. [ 31 ] However, the existing models involving a long‐range composition gradient [ 29,32,33 ] are clearly irrelevant to the novel bulk τ DL we establish in this work.…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…They are categorized as following four major schemes.

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 ( Cai et al., 2017 ; Cao et al., 2020 ). Copyrights 2014, 2017, Springer Nature; Copyrights 2019, 2020, John Wiley & Sons, Inc.

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“…However, the switching contribution from the perpendicular STT current and its damage to the fragile tunneling barrier have to be balanced. Most recently, a novel lateral SOT was demonstrated in locally laser annealed Pt/Co/Pt trilayers, where was generated from the laser-induced lateral local Pt-rich region inside the nominal Co layer ( Cao et al., 2020 ). The current-induced an out-of-plane effective field and thereby zero-field magnetization switching was then achieved, the switching sense of which depends only on the relative location of the Pt-rich and the Co-rich regions, regardless of the net spin polarization of external spin current from both the bottom and the top Pt layers.…”

“…Subsequently, the SOC layer is etched to form the two or three terminals device, and the gap filling is to be implemented following with chemical mechanical planarization. Also note that most recently reported SOTs in various single magnetic layers could help to facilitate the development of SOT-MTJs without the SOC layer ( Wang et al., 2012 ; Amin et al., 2019 ; Luo et al., 2019b ; Liu et al., 2020a ; Zhang et al., 2020a ; Tang et al., 2020 ; Cao et al., 2020 ). Eventually, a dual damascene Cu or TiN electrode will be fabricated to complete the electrical connection for routing and testing.…”

Growth, strain, and spin-orbit torques in epitaxial Ni-Mn-Sb films sputtered on GaAs

“…This mechanism can be exploited to exert magnetic torques within multilayers of ferromagnetic and heavy high spin-orbit coupling metals [21,22]. These two types of spin torques originate from the spin-orbit transport effects, often termed spin-orbit torques, and have been widely studied in many different film stacks [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37].…”