An antidamping spin–orbit torque originating from the Berry curvature

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Abstract

Magnetization switching at the interface between ferromagnetic and paramagnetic metals, controlled by current-induced torques, could be exploited in magnetic memory technologies. Compelling questions arise regarding the role played in the switching by the spin Hall effect in the paramagnet and by the spin–orbit torque originating from the broken inversion symmetry at the interface. Of particular importance are the antidamping components of these current-induced torques acting against the equilibrium-restoring Gilbert damping of the magnetization dynamics. Here, we report the observation of an antidamping spin–orbit torque that stems from the Berry curvature, in analogy to the origin of the intrinsic spin Hall effect. We chose the ferromagnetic semiconductor (Ga,Mn)As as a material system because its crystal inversion asymmetry allows us to measure bare ferromagnetic films, rather than ferromagnetic–paramagnetic heterostructures, eliminating by design any spin Hall effect contribution. We provide an intuitive picture of the Berry curvature origin of this antidamping spin–orbit torque as well as its microscopic modelling. We expect the Berry curvature spin–orbit torque to be of comparable strength to the spin-Hall-effect-driven antidamping torque in ferromagnets interfaced with paramagnets with strong intrinsic spin Hall effect.

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Figure 1: Spin–orbit coupling and antidamping SOT.
Figure 2: Spin–orbit FMR experiment.
Figure 3: In-plane and out-of-plane SOT fields.
Figure 4: Theoretical modelling of measured angular dependencies of SOT fields.

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Acknowledgements

The authors acknowledge support from the EU European Research Council (ERC) advanced grant no. 268066, from the Ministry of Education of the Czech Republic grant no. LM2011026, from the Grant Agency of the Czech Republic grant no. 14-37427G, from the Academy of Sciences of the Czech Republic Praemium Academiae, and support from US grants ONR-N000141110780, NSF-DMR-1105512 and NSF TAMUS LSAMP BTD award 1026774. A.J.F. acknowledges support from a Hitachi research fellowship. H.K. acknowledges financial support from the Japan Science and Technology Agency (JST).

Author information

Theory and data modelling were performed by T.J., E.K.V., L.P.Z., K.V. and J.S. Materials were prepared by V.N., R.P.C. and B.L.G. Sample preparation was performed by A.C.I. Experiments and data analysis were carried out by H.K., D.F., J.W. and A.J.F. The manuscript was written by T.J., A.J.F., H.K. and J.S., and project planning was performed by T.J., A.J.F., J.S. and H.K.

Correspondence to A. J. Ferguson.

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Kurebayashi, H., Sinova, J., Fang, D. et al. An antidamping spin–orbit torque originating from the Berry curvature. Nature Nanotech 9, 211–217 (2014). https://doi.org/10.1038/nnano.2014.15

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