Spin-orbit torque (SOT) is an emerging technology that enables the efficient manipulation of spintronic devices. The initial processes of interest in SOTs involved electric fields, spin-orbit coupling, conduction electron spins, and magnetization. More recently, interest has grown to include a variety of other processes that include phonons, magnons, or heat. Over the past decade, many materials have been explored to achieve a larger SOT efficiency. Recently, holistic design to maximize the performance of SOT devices has extended material research from a nonmagnetic layer to a magnetic layer. The rapid development of SOT has spurred a variety of SOT-based applications. In this article, we first review the theories of SOTs by introducing the various mechanisms thought to generate or control SOTs, such as the spin Hall effect, the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients, magnons, and strain effects. Then, we discuss the materials that enable these effects, including metals, metallic alloys, topological insulators, 2-D materials, and complex oxides. We also discuss the important roles in SOT devices of different types of magnetic layers, such as magnetic insulators, antiferromagnets, and ferrimagnets. Afterward, we discuss device applications utilizing SOTs. We discuss and compare three- and two-terminal SOT-magnetoresistive random access memories (MRAMs); we mention various schemes to eliminate the need for an external field. We provide technological application considerations for SOT-MRAM and give perspectives on SOT-based neuromorphic devices and circuits. In addition to SOT-MRAM, we present SOT-based spintronic terahertz generators, nano-oscillators, and domain-wall and skyrmion racetrack memories. This article aims to achieve a comprehensive review of SOT theory, materials, and applications, guiding future SOT development in both the academic and industrial sectors.
|Original language||English (US)|
|Journal||IEEE Transactions on Magnetics|
|State||Published - Jul 1 2021|
Bibliographical noteFunding Information:
Qiming Shao, Peng Li, and Wei Zhang coordinated this roadmap. The work of Wei Zhang was supported by the National Science Foundation under Award ECCS-1941426. The work of Qiming Shao was supported by the Hong Kong Research Grants Council–Early Career Scheme under Grant 26200520. The work of Luqiao Liu was supported by the National Science Foundation under Award ECCS-1808826. The work of Hyunsoo Yang was supported in part by the Advanced Manufacturing and Engineering-Individual Research Grant (AME-IRG) through RIE2020 funds under Grant A1983c0037 and in part by the NUS Hybrid-Integrated Flexible Electronic Systems Program. The work of Shunsuke Fukami was supported in part by the Japan Society for the Promotion of Science (JSPS) Kakenhi under Grant 19H05622 and in part by JST-CREST under Grant JPMJCR19K3. The work of Frank Freimuth and Yuriy Mokrousov was supported by the Deutsche Forschungs-gemeinschaft (DFG, German Research Foundation) under Grant TRR 173-268565370 (Project A11). The work of Axel Hoffmann and Mark Stiles were supported by Quantum Materials for Energy Efficient Neuromorphic Computing, an Energy Frontier Research Center funded by the U.S. DOE, Office of Science, under Award DE-SC0019273. The work of Kevin Garello was supported by the IMEC’s Industrialization Affiliation Program on magnetoresistive random-access memory (MRAM) devices. The authors would like to thank Laith Alahmed for his careful reading of the manuscript.
© 1965-2012 IEEE.
- Magnetic devices
- magnetic materials
- magnetic memory
- spin-orbit torques (SOTs)