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Mutual phase-locking of microwave spin torque nano-oscillators

Nature volume 437, pages 389–392 (2005)Cite this article

Abstract

The spin torque1,2 effect that occurs in nanometre-scale magnetic multilayer devices can be used to generate steady-state microwave signals in response to a d.c. electrical current3,4,5,6,7,8. This establishes a new functionality for magneto-electronic structures that are more commonly used as magnetic field sensors and magnetic memory elements9. The microwave power emitted from a single spin torque nano-oscillator (STNO) is at present typically less than 1 nW. To achieve a more useful power level (on the order of microwatts), a device could consist of an array of phase coherent STNOs, in a manner analogous to arrays of Josephson junctions and larger semiconductor oscillators10,11,12. Here we show that two STNOs in close proximity mutually phase-lock—that is, they synchronize, which is a general tendency of interacting nonlinear oscillator systems13,14,15. The phase-locked state is distinct, characterized by a sudden narrowing of signal linewidth and an increase in power due to the coherence of the individual oscillators. Arrays of phase-locked STNOs could be used as nanometre-scale reference oscillators. Furthermore, phase control of array elements (phased array) could lead to nanometre-scale directional transmitters and receivers for wireless communications.

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Figure 1: Structure and basic behaviour of a two-nano-contact device.
Figure 2: Locking behaviour.
Figure 3: Behaviour of individual oscillators.
Figure 4: Device power outputs.

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Acknowledgements

We thank P. Kabos and A. Kos for assistance with microwave apparatus, and A. Slavin, M. Stiles, T. Gerrits and R. Goldfarb for discussions. This work was partly supported by the US government.

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Authors and Affiliations

  1. Electromagnetic Technology Division, National Institute of Standards and Technology, Colorado, 80305, Boulder, USA

    Shehzaad Kaka, Matthew R. Pufall, William H. Rippard, Thomas J. Silva & Stephen E. Russek

  2. Hitachi San Jose Research Center, San Jose, California, 95120, USA

    Jordan A. Katine

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  1. Shehzaad Kaka
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Correspondence to Shehzaad Kaka.

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Kaka, S., Pufall, M., Rippard, W. et al. Mutual phase-locking of microwave spin torque nano-oscillators. Nature 437, 389–392 (2005). https://doi.org/10.1038/nature04035

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