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Time-resolved measurement of spin-transfer-driven ferromagnetic resonance and spin torque in magnetic tunnel junctions

Nature Physics volume 7, pages 496–501 (2011)Cite this article

Abstract

The bias dependence of the torque that a spin-polarized current exerts on ferromagnetic elements is important for understanding fundamental spin physics in magnetic devices and for applications. Several experimental techniques have been introduced in recent years in attempts to measure spin-transfer torque in magnetic tunnel junctions. However, these techniques have provided only indirect measures of the torque and their results regarding bias dependence are qualitatively and quantitatively inconsistent. Here we demonstrate that spin torque in magnetic tunnel junctions can be measured directly by using time-domain techniques to detect resonant magnetic precession in response to an oscillating spin torque. The technique is accurate in the high-bias regime relevant for applications, and because it detects directly small-angle linear-response magnetic dynamics caused by spin torque it is relatively immune to artefacts affecting competing techniques. At high bias we find that the spin-torque vector differs markedly from the simple lowest-order Taylor series approximations commonly assumed.

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Figure 1: Overview of the experiment.
Figure 2: Time-resolved measurements of spin-torque-driven magnetic resonance.
Figure 3: Measured bias dependence of the spin-transfer torque vector.

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Acknowledgements

We thank D. Mauri of Hitachi Global Storage Technologies (now at Western Digital Corp.) for providing the junction thin film stacks that we used to fabricate the tunnel junctions. Cornell acknowledges support from ARO, ONR, DARPA, NSF (DMR-1010768), and 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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Authors and Affiliations

  1. Cornell University, Ithaca, New York 14853, USA

    Chen Wang, Yong-Tao Cui, Robert A. Buhrman & Daniel C. Ralph

  2. Hitachi Global Storage Technologies, San Jose Res. Ctr., San Jose, California 95135, USA

    Jordan A. Katine

  3. Kavli Institute at Cornell, Cornell University, Ithaca, New York 14853, USA

    Daniel C. Ralph

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  1. Chen Wang
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  3. Jordan A. Katine
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Contributions

C.W. played the primary role in designing and performing the experiment and analysing the data. J.A.K. led the sample fabrication. Y-T.C. assisted in the measurements. All of the authors contributed to the data analysis and the preparation of the manuscript.

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Correspondence to Daniel C. Ralph.

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The authors declare no competing financial interests.

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Wang, C., Cui, YT., Katine, J. et al. Time-resolved measurement of spin-transfer-driven ferromagnetic resonance and spin torque in magnetic tunnel junctions. Nature Phys 7, 496–501 (2011). https://doi.org/10.1038/nphys1928

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