Abstract
The transfer of spin angular momentum from a spin-polarized current to a ferromagnet can generate sufficient torque to reorient the magnet’s moment. This torque could enable the development of efficient electrically actuated magnetic memories and nanoscale microwave oscillators. Yet difficulties in making quantitative measurements of the spin-torque vector have hampered understanding. Here we present direct measurements of both the magnitude and direction of the spin torque in magnetic tunnel junctions, the type of device of primary interest for applications. At low bias V, the differential torque dτ/dV lies in the plane defined by the electrode magnetizations, and its magnitude is in excellent agreement with recent predictions for near-perfect spin-polarized tunnelling. We find that the strength of the in-plane differential torque remains almost constant with increasing bias, despite a substantial decrease in the device magnetoresistance, and that with bias the torque vector also rotates out of the plane.
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Acknowledgements
We thank Y. Nagamine, D. D. Djayaprawira, N. Watanabe and K. Tsunekawa of Canon ANELVA Corp. for providing the junction thin-film stack we used to fabricate the tunnel-junction devices in this study, and G. D. Fuchs and K. V. Thadani for discussions. J.Z.S. would like to acknowledge discussions with S. Assefa, W. J. Gallagher on sample processing techniques, X. Jiang and S. S. P. Parkin for sample fabrication assistance, M. Rooks and N. Ruiz for e-beam lithography support and the support of the IBM MRAM team as a whole. Cornell acknowledges support from the Office of Naval Research, from the NSF (DMR-0605742) and from the NSF/NSEC program through the Cornell Center for Nanoscale Systems. We also acknowledge NSF support through use of the Cornell Nanofabrication Facility/NNIN and the Cornell Center for Materials Research facilities.
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The first author played the primary role in making the measurements and analysing the data. J.Z.S. led the sample fabrication. Y.T.C. and J.Z.S. assisted in making measurements. All of the authors contributed to the data analysis and the preparation of the manuscript.
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Supplementary Material and Supplementary Figures S1 – S6 (PDF 256 kb)
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Sankey, J., Cui, YT., Sun, J. et al. Measurement of the spin-transfer-torque vector in magnetic tunnel junctions. Nature Phys 4, 67–71 (2008). https://doi.org/10.1038/nphys783
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DOI: https://doi.org/10.1038/nphys783
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