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Inertial spin dynamics in ferromagnets

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.

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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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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