Tuning a binary ferromagnet into a multi-state synapse with spin-orbit-torque-induced plasticity

Cao, Yi; Rushforth, Andrew; Sheng, Yu; Zheng, Houzhi; Wang, Kaiyou

Abstract

Ferromagnets with binary states are limited for applications as artificial synapses for neuromorphic computing. Here, it is shown how synaptic plasticity of a perpendicular ferromagnetic layer (FM1) can be obtained when it is interlayer exchange‐coupled by another in‐plane ferromagnetic layer (FM2), where a magnetic field‐free current‐driven multistate magnetization switching of FM1 in the Pt/FM1/Ta/FM2 structure is induced by spin–orbit torque. Current pulses are used to set the perpendicular magnetization state, which acts as the synapse weight, and spintronic implementation of the excitatory/inhibitory postsynaptic potentials and spike timing‐dependent plasticity are demonstrated. This functionality is made possible by the action of the in‐plane interlayer exchange coupling field which leads to broadened, multistate magnetic reversal characteristics. Numerical simulations, combined with investigations of a reference sample with a single perpendicular magnetized Pt/FM1/Ta structure, reveal that the broadening is due to the in‐plane field component tuning the efficiency of the spin–orbit torque to drive domain walls across a landscape of varying pinning potentials. The conventionally binary FM1 inside the Pt/FM1/Ta/FM2 structure with an inherent in‐plane coupling field is therefore tuned into a multistate perpendicular ferromagnet and represents a synaptic emulator for neuromorphic computing, demonstrating a significant pathway toward a combination of spintronics and synaptic electronics.

Citation

Cao, Y., Rushforth, A., Sheng, Y., Zheng, H., & Wang, K. (2019). Tuning a binary ferromagnet into a multi-state synapse with spin-orbit-torque-induced plasticity. Advanced Functional Materials, 29(25), Article 1808104. https://doi.org/10.1002/adfm.201808104

• Journal Article Type: Article
• Acceptance Date: Mar 1, 2019
• Online Publication Date: Mar 12, 2019
• Publication Date: Mar 12, 2019
• Deposit Date: Mar 13, 2019
• Publicly Available Date: Mar 13, 2020
• Journal: Advanced Functional Materials
• Print ISSN: 1616-301X
• Electronic ISSN: 1616-3028
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 29
• Issue: 25
• Article Number: 1808104
• DOI: https://doi.org/10.1002/adfm.201808104
• Keywords: Spin-orbit torques (SOTs); Multi-state magnetization switching; Interlayer exchange coupling; Synaptic plasticity; Spike timing-dependent plasticity (STDP)
• Public URL: https://nottingham-repository.worktribe.com/output/1635177
• Publisher URL: https://doi.org/10.1002/adfm.201808104
• Additional Information: This is the peer reviewed version of the following article: Cao, Y., Rushforth, A. W., Sheng, Y., Zheng, H., Wang, K., Adv. Funct. Mater. 2019, 1808104. https://doi.org/10.1002/adfm.201808104 , which has been published in final form at https://doi.org/10.1002/adfm.201808104 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions
• Contract Date: Mar 14, 2019