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Excitations of incoherent spin-waves due to spin-transfer torque

Nature Materials volume 3, pages 877–881 (2004)Cite this article

Abstract

The possibility of exciting microwave oscillations in a nanomagnet by a spin-polarized current, as predicted by Slonczewski1 and Berger2, has recently been demonstrated3. This observation opens important prospects of applications in radiofrequency components. However, some unresolved inconsistencies are found when interpreting the magnetization dynamics within the coherent spin-torque model4,5,6. In some cases, the telegraph noise caused by spin-currents could not be quantitatively described by that model. This has led to controversy about the need for an effective magnetic temperature model7,8,9,10,11. Here we interpret the experimental results of Kiselev et al.3 using micromagnetic simulations. We point out the key role played by incoherent spin-wave excitation due to spin-transfer torque. The incoherence is caused by spatial inhomogeneities in local fields generating distributions of local precession frequencies. We observe telegraph noise with gigahertz frequencies at zero temperature. This is a consequence of the chaotic dynamics and is associated with transitions between attraction wells in phase space.

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Figure 2: Magnetization switching due to spin-transfer torque.
Figure 1: Calculated phase diagram of the normalized magnetoresistance (ΔR/Rmax) with varying currents and fields.
Figure 3: Contour of microwave power.
Figure 4: Telegraph noise at zero temperature and effective magnetic temperature.

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Acknowledgements

We thank A. Vedyaev, U. Ebels and I. N. Krivorotov for discussions.

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Authors and Affiliations

  1. SPINTEC — Unité de Recherche Associée CEA/DSM & CNRS/SPM-STIC, CEA Grenoble, Grenoble, 38054, France

    Kyung-Jin Lee, Alina Deac, Olivier Redon, Jean-Pierre Nozières & Bernard Dieny

  2. CEA/DRT/LETI–CEA/GRE, 17 Rue des Martyrs, Grenoble, 38054 Cedex 9, France

    Kyung-Jin Lee, Alina Deac & Olivier Redon

  3. Storage Laboratory, Samsung Advanced Institute of Technology, Suwon, Korea

    Kyung-Jin Lee

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  1. Kyung-Jin Lee
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  2. Alina Deac
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Correspondence to Kyung-Jin Lee.

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Lee, KJ., Deac, A., Redon, O. et al. Excitations of incoherent spin-waves due to spin-transfer torque. Nature Mater 3, 877–881 (2004). https://doi.org/10.1038/nmat1237

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