Direct observation of a propagating spin wave induced by spin-transfer torque

Journal name:
Nature Nanotechnology
Volume:
6,
Pages:
635–638
Year published:
DOI:
doi:10.1038/nnano.2011.140
Received
Accepted
Published online

Abstract

Spin torque oscillators with nanoscale electrical contacts1, 2, 3, 4 are able to produce coherent spin waves in extended magnetic films, and offer an attractive combination of electrical and magnetic field control, broadband operation5, 6, fast spin-wave frequency modulation7, 8, 9, and the possibility of synchronizing multiple spin-wave injection sites10, 11. However, many potential applications rely on propagating (as opposed to localized) spin waves, and direct evidence for propagation has been lacking. Here, we directly observe a propagating spin wave launched from a spin torque oscillator with a nanoscale electrical contact into an extended Permalloy (nickel iron) film through the spin transfer torque effect. The data, obtained by wave-vector-resolved micro-focused Brillouin light scattering, show that spin waves with tunable frequencies can propagate for several micrometres. Micromagnetic simulations provide the theoretical support to quantitatively reproduce the results.

At a glance

Figures

  1. Schematic sample layout.
    Figure 1: Schematic sample layout.

    Cross-section of the sample, revealing the layers of the spin valve mesa and the active area of the STO device. An aluminium coplanar waveguide is deposited onto the spin valve mesa, and an optical window is etched into the central conductor of the waveguide close to the nanocontact.

  2. Characterization of the optical window.
    Figure 2: Characterization of the optical window.

    a, Scanning electron microscope image of a processed device, showing the optical window in the central conductor of the aluminium waveguide, the nanocontact approximate position and the line (dotted arrow) across which the μ-BLS laser spot was scanned. b, EDS data acquired in regions outside and inside the etched window (indicated by dashed and solid squares in a, respectively). Inset: experimental μ-BLS spectra (Stokes side), measured outside and inside the etched optical window in the absence of any injected current and within an applied perpendicular field of 2.0 kOe, revealing the presence of thermal spin waves.

  3. Spin-wave frequencies as a function of the injected d.c. intensity.
    Figure 3: Spin-wave frequencies as a function of the injected d.c. intensity.

    Measured (filled symbols) and simulated (open symbols) spin-wave frequency dependence on d.c. intensity for two different values of the magnetic field. Dashed lines represent the calculated FMR frequency. Inset: μ-BLS spectra (Stokes side) recorded at μ0Hext = 0.6 T and for different signs of the current |I| = 70 mA.

  4. Proof of spin-wave propagation.
    Figure 4: Proof of spin-wave propagation.

    a, Schematic of the experimental procedure used to prove the propagating character of the detected spin wave. KL and KSW represent the wave vectors of the incoming light and of the emitted spin wave, respectively. b, Measured μ-BLS spectra (I = 70 mA and μ0H = 0.6 T) corresponding to the case of fully opened (bottom spectrum) and partially closed (upper spectra) collected beam.

  5. Spin-wave attenuation as a function of distance from the STO.
    Figure 5: Spin-wave attenuation as a function of distance from the STO.

    Integrated intensity (symbols) of the spin-wave excitations detected using μ-BLS as a function of distance from the centre of the point contact (r). Analytical calculation (line) of the decay obtained using the function described in the text. Inset: simulated spin-wave wavelength as a function of applied d.c. intensity.

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Author information

  1. These authors contributed equally to this work

    • M. Madami &
    • S. Bonetti

Affiliations

  1. CNISM, Unità di Perugia and Dipartimento di Fisica, Università di Perugia, Via A. Pascoli, I-06123 Perugia, Italy

    • M. Madami,
    • S. Tacchi,
    • G. Carlotti &
    • G. Gubbiotti
  2. Materials Physics, School of Information Communication Technology, KTH – Royal Institute of Technology, Electrum 229, 164 40, Kista, Sweden

    • S. Bonetti &
    • J. Åkerman
  3. Dipartimento di Scienze per l'Ingegneria e l'Architettura, Università di Messina C.da di Dio, I-98166 Messina, Italy

    • G. Consolo
  4. CNISM, Unità di Ferrara, Via G. Saragat 1, I-44100 Ferrara, Italy

    • G. Consolo
  5. Centro S3, CNR-Istituto di Nanoscienze, Via Campi 213A, I-41125 Modena, Italy

    • G. Carlotti
  6. Istituto Officina dei Materiali del CNR (CNR-IOM), Unità di Perugia, c/o Dipartimento di Fisica, Via A. Pascoli, I-06123 Perugia, Italy

    • G. Gubbiotti
  7. Everspin Technologies, Inc., 1347 N. Alma School Road, Suite 220, Chandler, Arizona 85224, USA

    • F. B. Mancoff
  8. Functional Materials Division, School of Information Communication Technology, KTH – Royal Institute of Technology, Electrum 229, 164 40, Kista, Sweden

    • M. A. Yar
  9. Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden

    • J. Åkerman

Contributions

M.M., G.G., S.T. and G.Ca. performed μ-BLS measurements. S.B., M.A.Y. and J.Å. realized the procedure to open the optical access to the sample and performed EDS measurements. F.B.M. fabricated the original samples. G.Co. performed numerical simulations. All authors co-wrote the manuscript.

Competing financial interests

The authors declare no competing financial interests.

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