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Direct observation and mapping of spin waves emitted by spin-torque nano-oscillators

Nature Materials volume 9, pages 984–988 (2010)Cite this article

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Abstract

Dynamics induced by spin-transfer torque is a quickly developing topic in modern magnetism, which has initiated several new approaches to magnetic nanodevices1,2,3,4,5,6,7,8,9,10,11. It is now well established that a spin-polarized electric current injected into a ferromagnetic layer through a nanocontact exerts a torque on the magnetization, leading to microwave-frequency precession detectable through the magnetoresistance effect. This phenomenon provides a way for the realization of tunable nanometre-size microwave oscillators, the so-called spin-torque nano-oscillators3,4,6 (STNOs). Present theories of STNOs are mainly based on pioneering works12,13 predicting emission of spin waves due to the spin torque. Despite intense experimental studies, until now this spin-wave emission has not been observed. Here, we report the first experimental observation and two-dimensional mapping of spin waves emitted by STNOs. We demonstrate that the emission is strongly directional, and the direction of the spin-wave propagation is steerable by the magnetic field. The information about the emitted spin waves obtained in our measurements is of key importance for the understanding of the physics of STNOs, and for the implementation of coupling between individual oscillators mediated by spin waves9,10,11,14. Analysis shows that the observed directional emission is a general property inherent to any dynamical system with strongly anisotropic dispersion.

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Figure 1: Layout and characterization of the dynamical properties of STNOs.
Figure 2: Normalized colour-coded intensity maps of spin waves emitted by the STNOs.
Figure 3: Spectral characterization of the spin-wave emission.
Figure 4: Analysis of the relationship between the spin-wave spectrum and the spin-wave emission.

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Acknowledgements

We acknowledge support from Deutsche Forschungsgemeinschaft, the European Project Master (No. NMP-FP7 212257), NSF, the Research Corporation and the WVNano initiative.

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Authors and Affiliations

  1. Institute for Applied Physics and Center for Nonlinear Science, University of Muenster, Corrensstasse 2-4, 48149 Muenster, Germany

    Vladislav E. Demidov & Sergej O. Demokritov

  2. Department of Physics, West Virginia University, Morgantown, West Virginia 26506, USA

    Sergei Urazhdin

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  1. Vladislav E. Demidov
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Contributions

V.E.D. carried out measurements and data analysis, S.U. fabricated the samples and S.O.D. formulated the experimental approach and designed the measurement instrumentation. All authors co-wrote the manuscript.

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Correspondence to Vladislav E. Demidov.

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The authors declare no competing financial interests.

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Demidov, V., Urazhdin, S. & Demokritov, S. Direct observation and mapping of spin waves emitted by spin-torque nano-oscillators. Nature Mater 9, 984–988 (2010). https://doi.org/10.1038/nmat2882

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