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Long spin coherence length and bulk-like spin–orbit torque in ferrimagnetic multilayers

Nature Materials volume 18, pages 29–34 (2019)Cite this article

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Abstract

Spintronics relies on magnetization switching through current-induced spin torques. However, because spin transfer torque for ferromagnets is a surface torque, a large switching current is required for a thick, thermally stable ferromagnetic cell, and this remains a fundamental obstacle for high-density non-volatile applications with ferromagnets. Here, we report a long spin coherence length and associated bulk-like torque characteristics in an antiferromagnetically coupled ferrimagnetic multilayer. We find that a transverse spin current can pass through >10-nm-thick ferrimagnetic Co/Tb multilayers, whereas it is entirely absorbed by a 1-nm-thick ferromagnetic Co/Ni multilayer. We also find that the switching efficiency of Co/Tb multilayers partially reflects a bulk-like torque characteristic, as it increases with ferrimagnet thickness up to 8 nm and then decreases, in clear contrast to the 1/thickness dependence of ferromagnetic Co/Ni multilayers. Our results on antiferromagnetically coupled systems will invigorate research towards the development of energy-efficient spintronics.

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Fig. 1: Semiclassical illustration of increased spin coherence length in FIMs compared to ferromagnets.
Fig. 2: SOTs in ferromagnetic versus ferrimagnetic film stacks.
Fig. 3: SOT effective fields and switching efficiencies in ferromagnetic versus ferrimagnetic multilayers.
Fig. 4: Spin pumping measurements.
Fig. 5: Characterizations of CoTb alloy samples.

Data availability

The data supporting the findings of this study are available within the paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors acknowledge discussions with P.M. Haney. This research was supported by the National Research Foundation (NRF), Prime Minister’s Office, Singapore, under its Competitive Research Programme (CRP award no. NRFCRP12-2013-01). K.-J.L. was supported by the National Research Foundation of Korea (NRF-2015M3D1A1070465 and NRF-2017R1A2B2006119) and the KIST Institutional Program (project no. 2V05750) and Samsung Research Funding Center of Samsung Electronics under project no. SRFCMA1702-02.

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Author notes

  1. These authors contributed equally: Do Bang, Rahul Mishra

Authors and Affiliations

  1. Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore

    Jiawei Yu, Rahul Mishra, Rajagopalan Ramaswamy, Yi Wang, Shuyuan Shi & Hyunsoo Yang

  2. Toyota Technological Institute, Tempaku, Nagoya, Japan

    Do Bang, Pham Van Thach & Hiroyuki Awano

  3. Institute of Materials Science, Vietnam Academy of Science and Technology, Hanoi, Vietnam

    Do Bang & Pham Van Thach

  4. Department of Materials Science and Engineering, Korea University, Seoul, Korea

    Jung Hyun Oh, Dong-Kyu Lee, Gyungchoon Go, Seo-Won Lee & Kyung-Jin Lee

  5. KU-KIST Graduate School of Conversing Science and Technology, Korea University, Seoul, Korea

    Hyeon-Jong Park & Kyung-Jin Lee

  6. Department of Semiconductor Systems Engineering, Korea University, Seoul, Korea

    Yunboo Jeong & Kyung-Jin Lee

  7. Shanghai Key Laboratory of Special Artificial Macrostructure Materials and Technology and School of Physics Science and Engineering, Tongji University, Shanghai, China

    Xuepeng Qiu

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  1. Jiawei Yu
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Contributions

J.Y. and H.Y. planned the project. J.Y., D.B. and P.V.T. deposited films. J.Y. and R.M. fabricated devices and performed the transport measurements. J.Y., R.R., R.M., Y.W. and S.S. carried out the spin pumping measurements. J.H.O., H.-J.P., Y.J., D.-K.L., S.-W.L., G.G. and K.-J.L. performed theoretical analysis. J.Y., D.B., X.Q., R.M., Y.J. and G.G. analysed the data with the help of H.A., K.-J.L. and H.Y. All authors discussed the results and commented on the manuscript. J.Y., K.-J.L. and H.Y. wrote the manuscript. H.Y. initiated the idea and led the project.

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Correspondence to Kyung-Jin Lee or Hyunsoo Yang.

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Yu, J., Bang, D., Mishra, R. et al. Long spin coherence length and bulk-like spin–orbit torque in ferrimagnetic multilayers. Nature Mater 18, 29–34 (2019). https://doi.org/10.1038/s41563-018-0236-9

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