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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Slonczewski, J. C. Current-driven excitation of magnetic multilayers. J. Magn. Magn. Mater. 159, L1–L7 (1996)
Berger, L. Emission of spin waves by a magnetic multilayer traversed by a current. Phys. Rev. B 54, 9353–9358 (1996)
Katine, J. A., Albert, F. J., Buhrman, R. A., Myers, E. B. & Ralph, D. C. Current-driven magnetization reversal and spin wave excitations in Co/Cu/Co pillars. Phys. Rev. Lett. 84, 4212–4215 (2000)
Tsoi, M. et al. Generation and detection of phase-coherent current-driven magnons in magnetic multilayers. Nature 406, 46–48 (2000)
Kiselev, S. I. et al. Microwave oscillations of a nanomagnet driven by a spin-polarized current. Nature 425, 380–383 (2003)
Rippard, W. H., Pufall, M. R., Kaka, S., Russek, S. E. & Silva, T. J. Direct-current induced dynamics in Co90Fe10/Ni80Fe20 point contacts. Phys. Rev. Lett. 92, 27201 (2004)
Covington, M., Al Haj Darwish, M., Ding, Y., Gokemeijer, N. J. & Seigler, M. Current-induced magnetization dynamics in current perpendicular to the plane spin valves. Phys. Rev. B 69, 184406 (2004)
Krivorotov, I. N. et al. Time domain measurements of nanomagnet dynamics driven by spin-transfer torques. Science 307, 228–231 (2005)
Wolf, S. A. et al. Spintronics: a spin-based electronics vision for the future. Science 294, 1488–1495 (2001)
Benz, S. P. & Burroughs, C. J. Coherent emission from two dimensional Josephson junction arrays. Appl. Phys. Lett. 58, 2162–2164 (1991)
Wengler, M. J., Guan, B. & Track, E. K. 190-GHz radiation from a quasioptical Josephson junction array. IEEE Trans. Microwave Theory Tech. 43, 984–988 (1995)
Popovic, Z. B., Weikle, R. M., Kim, M. & Rutledge, D. B. A 100-MESFET planar grid oscillator. IEEE Microwave Theory Tech. 39, 193–200 (1991)
Strogatz, S. Sync: The Emerging Science of Spontaneous Order 51, 116 (Hyperion, New York, 2003)
York, R. A. Nonlinear analysis of phase relationships in quasi-optical oscillator arrays. IEEE Trans. Microwave Theory Tech. 41, 1799–1809 (1993)
Rezavi, B. A study of injection locking and pulling in oscillators. IEEE J. Solid State Circuits 39, 1415–1424 (2004)
Wiesenfeld, K., Colet, P. & Strogatz, S. H. Synchronization transitions in a disordered Josephson series array. Phys. Rev. Lett. 76, 404–407 (1996)
Finnegan, T. F. & Wahlsten, S. Observation of coherent microwave radiation emitted by coupled Josephson junctions. Appl. Phys. Lett. 21, 541–544 (1972)
Buck, J. & Buck, E. Mechanism of rhythmic synchronous flashing of fireflies. Science 159, 1319–1327 (1968)
Bennet, M., Schatz, M. F., Rockwood, H. & Wiesenfeld, K. Huygens's clocks. Proc. R. Soc. Lond. A 458, 563–579 (2002)
Suhl, H. The nonlinear behaviour of ferrites at high microwave signal levels. Proc. Inst. Radio Engrs. 44, 1270–1284 (1956)
Rippard, W. H., Pufall, M. R., Kaka, S., Silva, T. J. & Russek, S. E. Current-driven microwave dynamics in magnetic point contacts as a function of applied field angle. Phys. Rev. B 70, 100406 (2004)
Baibich, M. N. et al. Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices. Phys. Rev. Lett. 61, 2472–2475 (1988)
Slonczewski, J. C. Excitation of spin waves by an electric current. J. Magn. Magn. Mater. 195, L261–L268 (1999)
Rippard, W. H., Pufall, M. R., Kaka, S., Silva, T. J. & Russek, S. E. Injection locking and phase control of spin transfer oscillators. Phys. Rev. Lett. 95, 067203 (2005)
Russek, S. E., McMichael, R. D., Donahue, M. J. & Kaka, S. in Spin Dynamics in Confined Magnetic Structures II (eds Hillebrands, B. & Ounadjela, K.) 93–156 (Springer, Berlin, 2003)
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.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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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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