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Inertial spin dynamics in ferromagnets

Nature Physics volume 17, pages 245–250 (2021)Cite this article

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Abstract

The understanding of how spins move and can be manipulated at pico- and femtosecond timescales has implications for ultrafast and energy-efficient data-processing and storage applications. However, the possibility of realizing commercial technologies based on ultrafast spin dynamics has been hampered by our limited knowledge of the physics behind processes on this timescale. Recently, it has been suggested that inertial effects should be considered in the full description of the spin dynamics at these ultrafast timescales, but a clear observation of such effects in ferromagnets is still lacking. Here, we report direct experimental evidence of intrinsic inertial spin dynamics in ferromagnetic thin films in the form of a nutation of the magnetization at a frequency of ~0.5 THz. This allows us to reveal that the angular momentum relaxation time in ferromagnets is on the order of 10 ps.

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Fig. 1: Magnetic torque dynamics of a ferromagnet in the terahertz range.
Fig. 2: Coherent MOKE response of different thin-film ferromagnets.
Fig. 3: Effect of the driving field frequency on the phase of the response of the magnetization.
Fig. 4: Amplitude of the magnetization dynamics for narrowband terahertz fields.

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Data availability

Data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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Acknowledgements

We thank J. Lindner (HZDR, Dresden) for helpful discussions and Z. Wang and S. Germansky for experimental support. The research leading to this result has been partly supported by the project CALIPSOplus under grant agreement no. 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Parts of this research were carried out at ELBE at Helmholtz-Zentrum Dresden-Rossendorf e.V., a member of the Helmholtz Association. We thank U. Lehnert and J. Teichert for assistance and the ELBE team for operating the TELBE facility. S.K., B.G. and M.G. acknowledge support from the European Cluster of Advanced Laser Light Sources (EUCALL) project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 654220. N.A., I.I., M.G. and S.K. acknowledge support from the European Commission’s Horizon 2020 research and innovation programme, under grant agreement no. DLV-737038(TRANSPIRE). K.N., D.P., N.Z.H. and S.B. acknowledge support from the European Research Council, Starting Grant 715452 MAGNETIC-SPEED-LIMIT.

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Author notes

  1. These authors contributed equally: K. Neeraj, N. Awari.

Authors and Affiliations

  1. Department of Physics, Stockholm University, Stockholm, Sweden

    Kumar Neeraj, Debanjan Polley, Nanna Zhou Hagström & Stefano Bonetti

  2. Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

    Nilesh Awari, Sergey Kovalev, Bertram Green, Jan-Christoph Deinert, Igor Ilyakov, Min Chen & Mohammed Bawatna

  3. Institute of Physics, Chemnitz University of Technology, Chemnitz, Germany

    Sri Sai Phani Kanth Arekapudi & Olav Hellwig

  4. Faculty of Physics and CENIDE, University of Duisburg-Essen, Duisburg, Germany

    Anna Semisalova

  5. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

    Anna Semisalova, Kilian Lenz & Olav Hellwig

  6. DIETI, University of Naples Federico II, Naples, Italy

    Valentino Scalera & Claudio Serpico

  7. Department of Engineering, University of Naples ‘Parthenope’, Naples, Italy

    Massimiliano d’Aquino

  8. LSI, École Polytechnique, CEA/DRF/IRAMIS, CNRS, Institut Polytechnique de Paris, Palaiseau, France

    Jean-Eric Wegrowe

  9. Institute of Optical Sensor Systems, German Aerospace Center (DLR), Berlin, Germany

    Michael Gensch

  10. Institute of Optics and Atomic Physics, TU Berlin, Berlin, Germany

    Michael Gensch

  11. Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Venezia-Mestre, Italy

    Stefano Bonetti

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  1. Kumar Neeraj
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Contributions

S.B. designed the experiment. S.B. and M.G. coordinated the project. K.N., N.A., S.K., D.P., N.Z.H., B.G., J.-C.D., I.I., M.C., M.B., M.G. and S.B. performed the measurements at TELBE. K.N., N.A. and S.B. performed the data analysis. K.N., V.S., M.d’A. and C.S. performed the inertial LLG simulations. S.S.P.K.A., O.H., A.S. and K.L. fabricated and characterized the samples. K.N. and S.B. coordinated the work on the paper, with contributions from N.A., S.K., S.S.P.K.A., A.S., K.L., O.H., J.-E.W. and M.G. and discussions with all authors.

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Correspondence to Stefano Bonetti.

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Supplementary discussion: six sections including 18 figures.

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Neeraj, K., Awari, N., Kovalev, S. et al. Inertial spin dynamics in ferromagnets. Nat. Phys. 17, 245–250 (2021). https://doi.org/10.1038/s41567-020-01040-y

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