Phase-locking in double-point-contact spin-transfer devices

Article metrics


Spin-transfer1,2 in nanometre-scale magnetic devices results from the torque on a ferromagnet owing to its interaction with a spin-polarized current and the electrons' spin angular momentum. Experiments have detected either a reversal3,4,5,6,7,8,9,10,11,12,13,14,15,16 or high-frequency (GHz) steady-state precession17,18,19,20,21,22,23 of the magnetization in giant magnetoresistance spin valves and magnetic tunnel junctions with current densities of more than 107 A cm-2. Spin-transfer devices may enable high-density, low-power magnetic random access memory24,25 or direct-current-driven nanometre-sized microwave oscillators. Here we show that the magnetization oscillations induced by spin-transfer in two 80-nm-diameter giant-magnetoresistance point contacts in close proximity to each other can phase-lock into a single resonance over a frequency range from approximately <10 to >24 GHz for contact spacings of less than about 200 nm. The output power from these contact pairs with small spacing is approximately twice the total power from more widely spaced (400 nm and greater) contact pairs that undergo separate resonances, indicating that the closely spaced pairs are phase-locked with zero phase shift. Phase-locking may enable control of large arrays of coupled spin-transfer devices with increased power output for microwave oscillator applications.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Overview of double-point-contact device.
Figure 2: High-frequency output for devices with two 80-nm point contacts and varied intercontact spacing.
Figure 3: Histograms showing statistical distribution of spin-transfer behaviour in devices with two 80-nm-diameter contacts and varied centre-to-centre contact spacing.
Figure 4: High-frequency output for two 80-nm point contacts with 150-nm intercontact spacing.


  1. 1

    Slonczewski, J. C. Current-driven excitation of magnetic multilayers. J. Magn. Magn. Mater 159, L1–L7 (1996)

  2. 2

    Berger, L. Emission of spin waves by a magnetic multilayer traversed by a current. Phys. Rev. B 54, 9353–9358 (1996)

  3. 3

    Myers, E. B., Ralph, D. C., Katine, J. A., Louie, R. N. & Buhrman, R. A. Current-induced switching of domains in magnetic multilayer devices. Science 285, 867–870 (1999)

  4. 4

    Wegrowe, J.-E., Kelly, D., Jaccard, Y., Guittienne, Ph. & Ansermet, J.-Ph. Current-induced magnetization reversal in magnetic nanowires. Europhys. Lett. 45, 626–632 (1999)

  5. 5

    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, 3149–3152 (2000)

  6. 6

    Grollier, J. et al. Spin-polarized current induced switching in Co/Cu/Co pillars. Appl. Phys. Lett. 78, 3663–3665 (2001)

  7. 7

    Sun, J. Z., Monsma, D. J., Abraham, D. W., Rooks, M. J. & Koch, R. H. Batch-fabricated spin-injection magnetic switches. Appl. Phys. Lett. 81, 2202–2204 (2002)

  8. 8

    Urazhdin, S., Birge, N. O., Pratt, W. P. Jr & Bass, J. Current-driven magnetic excitations in permalloy-based multilayer nanopillars. Phys. Rev. Lett. 91, 146803 (2003)

  9. 9

    Mancoff, F. B. et al. Angular dependence of spin-transfer switching in a magnetic nanostructure. Appl. Phys. Lett. 83, 1596–1598 (2003)

  10. 10

    Huai, Y., Albert, F., Nguyen, P., Pakala, M. & Valet, T. Observation of spin-transfer switching in deep submicron-sized and low-resistance magnetic tunnel junctions. Appl. Phys. Lett. 84, 3118–3120 (2004)

  11. 11

    Ozyilmaz, B. et al. Current-induced magnetization reversal in high magnetic fields in Co/Cu/Co nanopillars. Phys. Rev. Lett. 91, 067203 (2003)

  12. 12

    Yagami, K., Tulapurkar, A. A., Fukushima, A. & Suzuki, Y. Low-current spin-transfer switching and its thermal durability in a low-saturation-magnetization nanomagnet. Appl. Phys. Lett. 85, 5634–5636 (2004)

  13. 13

    Jiang, Y. et al. Substantial reduction of critical current for magnetization switching in an exchange-biased spin valve. Nature Mater. 3, 361–363 (2004)

  14. 14

    Chen, T. Y., Ji, Y., Chien, C. L. & Stiles, M. D. Current-driven switching in a single exchange-biased ferromagnetic layer. Phys. Rev. Lett. 93, 026601 (2004)

  15. 15

    Lacour, D., Katine, J. A., Smith, N., Carey, M. J. & Childress, J. R. Thermal effects on the magnetic-field dependence of spin-transfer-induced magnetization reversal. Appl. Phys. Lett. 85, 4681–4683 (2004)

  16. 16

    Lee, K. J. et al. Spin transfer effect in spin-valve pillars for current-perpendicular-to-plane magnetoresistive heads. J. Appl. Phys. 95, 7423–7428 (2004)

  17. 17

    Tsoi, M. et al. Generation and detection of phase-coherent current-driven magnons in magnetic multilayers. Nature 406, 46–48 (2000)

  18. 18

    Kiselev, S. I. et al. Microwave oscillations of a nanomagnet driven by a spin-polarized current. Nature 425, 380–383 (2003)

  19. 19

    Covington, M., AlHajDarwish, M., Ding, Y., Gokemeijer, N. J. & Seigler, M. A. Current-induced magnetization dynamics in current perpendicular to the plane spin valves. Phys. Rev. B 69, 184406 (2004)

  20. 20

    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, 027201 (2004)

  21. 21

    Kiselev, S. I. et al. Current-induced nanomagnet dynamics for magnetic fields perpendicular to the sample plane. Phys. Rev. Lett. 93, 036601 (2004)

  22. 22

    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)

  23. 23

    Krivorotov, I. N. et al. Time-domain measurements of nanomagnet dynamics driven by spin-transfer torques. Science 307, 228–231 (2005)

  24. 24

    Engel, B. N. et al. A 4-Mbit toggle MRAM based on a novel bit and switching method. IEEE Trans. Mag. 41, 132–136 (2005)

  25. 25

    Parkin, S. S. P. et al. Exchange-biased magnetic tunnel junctions and application to nonvolatile magnetic random access memory. J. Appl. Phys. 85, 5828–5833 (1999)

  26. 26

    Russek, S. E., Kaka, S., Rippard, W. H., Pufall, M. R. & Silva, T. J. Finite-temperature modeling of nanoscale spin-transfer oscillators. Phys. Rev. B 71, 104425 (2005)

Download references


We thank W. H. Rippard, T. J. Silva and S. E. Russek for discussions. This work was supported in part by the DARPA SPINS programme through Motorola.

Author information

Correspondence to F. B. Mancoff.

Ethics declarations

Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.