Skyrmion-based artificial synapses for neuromorphic computing

Abstract

Since the experimental discovery of magnetic skyrmions achieved one decade ago 1 , there have been significant efforts to bring the virtual particles into all-electrical fully functional devices, inspired by their fascinating physical and topological properties suitable for future low-power electronics 2 . Here, we experimentally demonstrate such a deviceelectrically-operating skyrmion-based artificial synaptic device designed for neuromorphic computing. We present that controlled current-induced creation, motion, detection and deletion of skyrmions in ferrimagnetic multilayers can be harnessed in a single device at room temperature to imitate the behaviors of biological synapses. Using simulations, we demonstrate that such skyrmion-based synapses could be used to perform neuromorphic pattern-recognition computing using handwritten recognition data set, reaching to the accuracy of ~89%, comparable to the software-based training accuracy of ~94%. Chip-level simulation then highlights the potential of skyrmion synapse compared to existing technologies. Our findings experimentally illustrate the basic concepts of skyrmion-based fully functional electronic devices while providing a new building block in the emerging field of spintronics-based bio-inspired computing.

Walker Breakdown with a Twist: Dynamics of Multilayer Domain Walls and Skyrmions Driven by Spin-Orbit Torque

“…We first consider the dynamics of an isolated straight DW in a multilayer film with ultrathin magnetic (M) layers (T < l ex ) of thickness T = 1 nm, consisting of N = 15 multilayer repeats with a period of P = 6 nm separated by nonmagnetic spacer layers. Although the composition of spacer layers has no effect on the DW analysis, here we imply that they consist of heavy metal layers (H) and symmetry breaking layers (S) incorporated into an asymmetrically stacked heterostructure of [H/M/S] Ntype, similar to those studied in a number of recent experimental works in which room-temperature skyrmions have been stabilized [15,21,22,41,45,46,51,52]. We assume a saturation magnetization M s = 1.4 × 10 6 A/m, quality factor Q = 2K u /µ 0 M 2 s = 1.4 (where K u is the uniaxial magnetocrystalline anisotropy constant and µ 0 is the vacuum permeability), exchange stiffness A = 1.0 × 10 −11 J/m, and interfacial DMI, D = 1.0 mJ/m 2 , representative of typical experimental skyrmion-hosting multilayers [10,21,45,51,53,54].…”

“…Magnetic domain walls (DWs) [2, 3] and skyrmions [4,5], localized twists of the magnetization with particle-like characteristics, are of high interest as potential information carriers in spintronic devices, owing to their topological properties and facile manipulation by electric currents. In particular, the small size, enhanced stability, and ability to follow two-dimensional trajectories make skyrmions extremely promising for racetrack storage [6][7][8][9][10] or novel non-von Neumann computing architectures [11][12][13][14][15]. Pioneering early work on magnetic skyrmions focused on bulk noncentrosymmetric materials [16][17][18] with low ordering temperatures, or ultrathin metal films in which nanoscale skyrmions can be stabilized at a low temperature [19].…”

Static and dynamic properties of bimerons in a frustrated ferromagnetic monolayer

“…Since the first experimental observation, magnetic skyrmions have been extensively studied due to their particle-like nature [14,15] and large potential in advanced electronic and spintronic applications [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. So far, the creation, annihilation and manipulation of magnetic skyrmions have been realized in magnetic multilayers at room temperature [18][19][20][22][23][24][25][26][27][28][29][30], and a lot of skyrmion-based device applications have been proposed [31][32][33][34][35][36][37][38][39][40][41][42] and even demonstrated in roomtemperature experiments [43][44][45].…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…One representative solution is to utilize the current-induced domain wall motion within the FM free layer ( Sengupta et al., 2015a ; Lequeux et al., 2016 ; Yue et al., 2019 ; Yang et al., 2019c ; Siddiqui et al., 2019 ; Azam et al., 2020 ; Zhang et al., 2019b ), for instance, by tuning the pinning potential of FM domain wall motions, SOT-induced multilevel magnetization switching as well as the typical synaptic functionality of spike-timing dependent plasticity (STDP) have been experimentally demonstrated ( Cao et al., 2019 ). Other strategies include the fine-magnetic domain switching in antiferromagnetic (AFM) ( Wadley et al., 2016 ; Olejník et al., 2017 ; Shi et al., 2020 ) or AFM/FM ( Liu et al., 2020b ; Zhou et al., 2020 ; Yun et al., 2020 ) heterostructures where multiple ∼100 nm-sized binary FM domains fixed by the polycrystalline AFM could reverse independently under the applying current ( Fukami et al., 2016 ; Kurenkov et al., 2017 ; Borders et al., 2016 ) and the SOT-induced skyrmion (a topological magnetic state) motions where the number of skyrmions within the signal reading area is proposed to represent the analog synaptic weight ( Song et al., 2020a ). In addition to the above efforts that try to form holistic multilevel magnetization by combining in-plane distributed binary magnetic solitons, which are difficult to achieve scalable multilevel spin-orbitronic synapses, the methodologies of innovating multilevel magnetization with out-of-plane multilevel mechanisms might be more practical and warrant more reliable solutions ( Hong et al., 2018 ; Hu et al., 2020 ; Sheng et al., 2018b ).…”