Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers



Magnetoresistive effects are usually invariant on inversion of the magnetization direction. In non-centrosymmetric conductors, however, nonlinear resistive terms can give rise to a current dependence that is quadratic in the applied voltage and linear in the magnetization. Here we demonstrate that such conditions are realized in simple bilayer metal films where the spin–orbit interaction and spin-dependent scattering couple the current-induced spin accumulation to the electrical conductivity. We show that the longitudinal resistance of Ta|Co and Pt|Co bilayers changes when reversing the polarity of the current or the sign of the magnetization. This unidirectional magnetoresistance scales linearly with current density and has opposite sign in Ta and Pt, which we associate with the modification of the interface scattering potential induced by the spin Hall effect in these materials. Our results suggest a route to control the resistance and detect magnetization switching in spintronic devices using a two-terminal geometry, which applies also to heterostructures including topological insulators.

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Figure 1: Illustration of the unidirectional spin Hall magnetoresistance effect and sample layout.
Figure 2: Linear and nonlinear magnetoresistance.
Figure 3: Field and current dependence of the nonlinear magnetoresistance.
Figure 4: USMR as a function of NM thickness.
Figure 5: Modulation of the spin accumulation, spin-dependent electrochemical potential, and interface resistance by the SHE.


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This work was funded by the Swiss National Science Foundation (Grant No. 200021-153404) and the European Commission under the 7th Framework Program (SPOT project, Grant No. 318144).

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C.O.A., K.G. and P.G. planned the experiments; M.G., A.G., S.F.A. and C.O.A. carried out the sample growth and patterning; C.O.A., K.G. and A.G. performed the measurements; C.O.A. and P.G. analysed the data and wrote the manuscript. All authors contributed to the discussion of the data in the manuscript and Supplementary Information.

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Correspondence to Can Onur Avci or Pietro Gambardella.

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Avci, C., Garello, K., Ghosh, A. et al. Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers. Nature Phys 11, 570–575 (2015). https://doi.org/10.1038/nphys3356

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