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Spin currents and spin–orbit torques in ferromagnetic trilayers


Magnetic torques generated through spin–orbit coupling1,2,3,4,5,6,7,8 promise energy-efficient spintronic devices. For applications, it is important that these torques switch films with perpendicular magnetizations without an external magnetic field9,10,11,12,13,14. One suggested approach15 to enable such switching uses magnetic trilayers in which the torque on the top magnetic layer can be manipulated by changing the magnetization of the bottom layer. Spin currents generated in the bottom magnetic layer or its interfaces transit the spacer layer and exert a torque on the top magnetization. Here we demonstrate field-free switching in such structures and show that its dependence on the bottom-layer magnetization is not consistent with the anticipated bulk effects15. We describe a mechanism for spin-current generation16,17 at the interface between the bottom layer and the spacer layer, which gives torques that are consistent with the measured magnetization dependence. This other-layer-generated spin–orbit torque is relevant to energy-efficient control of spintronic devices.

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Fig. 1: Spin–orbit torque measurement in ferromagnetic trilayers.
Fig. 2: Azimuthal angle-dependent V in the CoFeB/Ti sample.
Fig. 3: The spin z component of spin currents.

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The authors acknowledge K.-W. Kim, H.-W. Lee and J. Sinova for discussion. This work was supported by the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF-2015M3D1A1070465). B.-G.P. acknowledges financial support from the NRF (NRF-2017R1A2A2A05069760), K.-J.L. from the NRF (NRF-2017R1A2B2006119) and K.-J.K. from the NRF (NRF-2016R1A5A1008184). V.P.A. acknowledges support under the Cooperative Research Agreement between the University of Maryland and the National Institute of Standards and Technology Center for Nanoscale Science and Technology, Award 70NANB14H209, through the University of Maryland.

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B.-G.P. and K.-J.L. planned and supervised the study. S.-h.C.B. and Y.-W.O. fabricated devices and performed spin–orbit torque measurements. G.-H.L. and K.-J.K. performed electrical measurements. V.P.A. and M.D.S. provided a theoretical explanation for the interface-generated spin current. G.G., S.-J.L. and K.-J.L. performed numerical simulations. K.-J.L., B.-G.P., V.P.A. and M.D.S. wrote the manuscript.

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Correspondence to Byong-Guk Park or Kyung-Jin Lee.

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Baek, Sh.C., Amin, V.P., Oh, YW. et al. Spin currents and spin–orbit torques in ferromagnetic trilayers. Nature Mater 17, 509–513 (2018).

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