Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Ultrafast spin transport as key to femtosecond demagnetization

Abstract

Irradiating a ferromagnet with a femtosecond laser pulse is known to induce an ultrafast demagnetization within a few hundred femtoseconds. Here we demonstrate that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently. We optically excite a Au/Ni layered structure in which the 30 nm Au capping layer absorbs the incident laser pump pulse and subsequently use the X-ray magnetic circular dichroism technique to probe the femtosecond demagnetization of the adjacent 15 nm Ni layer. A demagnetization effect corresponding to the scenario in which the laser directly excites the Ni film is observed, but with a slight temporal delay. We explain this unexpected observation by means of the demagnetizing effect of a superdiffusive current of non-equilibrium, non-spin-polarized electrons generated in the Au layer.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.

$32.00

All prices are NET prices.

Figure 1: The investigated layered structures that are optically excited by the femtosecond laser pulse.
Figure 2: Time evolution of the magnetization of the Ni layer, after excitation with a femtosecond laser pulse, as measured through the element-selective XMCD signal at the Ni L3 absorption edge and normalized to the value before time zero.
Figure 3: Calculated time evolution of the average magnetization of the Ni film, in the Au/Ni sample and in the Ni reference sample, for 33 and 13 mJ cm−2 incident pump fluence, respectively.
Figure 4: Calculated time- and depth-resolved magnetization change ΔM(z,t) induced by NEQ electron superdiffusion.

References

  1. Beaurepaire, E., Merle, J-C., Daunois, A. & Bigot, J-Y. Ultrafast spin dynamics in ferromagnetic nickel. Phys. Rev. Lett. 76, 4250–4253 (1996).

    Article  CAS  Google Scholar 

  2. Carpene, E. et al. Dynamics of electron–magnon interaction and ultrafast demagnetization in thin iron films. Phys. Rev. B 78, 174422 (2008).

    Article  Google Scholar 

  3. Krauß, M. et al. Ultrafast demagnetization of ferromagnetic transition metals: The role of the Coulomb interaction. Phys. Rev. B 80, 180407 (2009).

    Article  Google Scholar 

  4. Zhang, G. P., Hübner, W., Lefkidis, G., Bai, Y. & George, T. F. Paradigm of the time-resolved magneto-optical Kerr effect for femtosecond magnetism. Nature Phys. 5, 499–502 (2009).

    Article  CAS  Google Scholar 

  5. Bigot, J-Y., Vomir, M. & Beaurepaire, E. Coherent ultrafast magnetism induced by femtosecond laser pulses. Nature Phys. 5, 515–520 (2009).

    Article  CAS  Google Scholar 

  6. Koopmans, B. et al. Explaining the paradoxical diversity of ultrafast laser-induced demagnetization. Nature Mater. 9, 259–265 (2010).

    Article  CAS  Google Scholar 

  7. Kirilyuk, A., Kimel, A. V. & Rasing, Th. Ultrafast optical manipulation of magnetic order. Rev. Mod. Phys. 82, 2731–2784 (2010).

    Article  Google Scholar 

  8. Battiato, M., Carva, K. & Oppeneer, P. M. Superdiffusive spin transport as a mechanism of ultrafast demagnetization. Phys. Rev. Lett. 105, 027203 (2010).

    Article  CAS  Google Scholar 

  9. Stamm, C. et al. Femtosecond modification of electron localization and transfer of angular momentum in nickel. Nature Mater. 6, 740–743 (2007).

    Article  CAS  Google Scholar 

  10. Stamm, C., Pontius, N., Kachel, T., Wietstruk, M. & Dürr, H. A. Femtosecond X-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization. Phys. Rev. B 81, 104425 (2010).

    Article  Google Scholar 

  11. Windt, D. L. IMD-Software for modelling the optical properties of multilayer films. Comput. Phys. 12, 360–370 (1998).

    Article  CAS  Google Scholar 

  12. Hamrle, J., Ferré, J., Nývlt, M. & Visnovský, S. In-depth resolution of the magneto-optical Kerr effect in ferromagnetic multilayers. Phys. Rev. B 66, 224423 (2002).

    Article  Google Scholar 

  13. Malinowski, G. et al. Control of speed and efficiency of ultrafast demagnetization by direct transfer of spin angular momentum. Nature Phys. 4, 855–858 (2008).

    Article  CAS  Google Scholar 

  14. Melnikov, A. et al. Ultrafast transport of laser-excited spin-polarized carriers in Au/Fe/MgO(001). Phys. Rev. Lett. 107, 076601 (2011).

    Article  Google Scholar 

  15. Battiato, M., Carva, K. & Oppeneer, P. M. Theory of laser-induced ultrafast superdiffusive spin transport in layered heterostructures. Phys. Rev. B 86, 024404 (2012).

    Article  Google Scholar 

  16. Stöhr, J. & Siegmann, H. C. Magnetism: From Fundamentals to Nanoscale Dynamics (Springer, 2006).

    Google Scholar 

  17. Carva, K., Battiatio, M. & Oppeneer, P. M. Is the controversy over femtosecond magneto-optics really solved? Nature Phys. 7, 665–666 (2011).

    Article  CAS  Google Scholar 

  18. Carva, K., Battiato, M. & Oppeneer, P. M. Ab initio investigation of the Elliott–Yafet electron–phonon mechanism in laser-induced ultrafast demagnetization. Phys. Rev. Lett. 107, 207201 (2011).

    Article  CAS  Google Scholar 

  19. Essert, S. & Schneider, H. C. Electron–phonon scattering dynamics in ferromagnetic metals and their influence on ultrafast demagnetization processes. Phys. Rev. B 84, 224405 (2011).

    Article  Google Scholar 

  20. Neubrand, A. & Hess, P. Laser generation and detection of surface acoustic waves: Elastic properties of surface layers. J. Appl. Phys. 71, 227–238 (1992).

    Article  CAS  Google Scholar 

  21. Djordjevic, M. et al. Comprehensive view on ultrafast dynamics of ferromagnetic films. Phys. Status Solidi 3, 1347–1358 (2006).

    Article  CAS  Google Scholar 

  22. Wang, X. et al. Temperature dependence of electron–phonon thermalization and its correlation to ultrafast magnetism. Phys. Rev. B 81, 220301 (2010).

    Article  Google Scholar 

  23. Holldack, K., Kachel, T., Khan, S., Mitzner, R. & Quast, T. Characterization of laser-electron interaction at the BESSY II femtoslicing source. Phys. Rev. ST Accel. Beams 8, 040704 (2005).

    Article  Google Scholar 

  24. Khan, S., Holldack, K., Kachel, T., Mitzner, R. & Quast, T, T. Femtosecond undulator radiation from sliced electron bunches. Phys. Rev. Lett. 97, 074801 (2006).

    Article  CAS  Google Scholar 

  25. Thole, B. T., Carra, P., Sette, F. & van der Laan, G. X-ray circular dichroism as a probe of orbital magnetization. Phys. Rev. Lett. 68, 1943–1946 (1992).

    Article  CAS  Google Scholar 

  26. Carra, P., Thole, B. T., Altarelli, M. & Wang, X. X-ray circular dichroism and local magnetic fields. Phys. Rev. Lett. 70, 694–697 (1993).

    Article  CAS  Google Scholar 

  27. Zhukov, V. P., Chulkov, E. V. & Echenique, P. M. Lifetimes and inelastic mean free path of low-energy excited electrons in Fe, Ni, Pt, and Au: Ab initio GW+T calculations. Phys. Rev. B 73, 125105 (2006).

    Article  Google Scholar 

  28. Zhukov, V. P., Chulkov, E. V. & Echenique, P. M. GW+T theory of excited electron lifetimes in metals. Phys. Rev. B 72, 155109 (2005).

    Article  Google Scholar 

Download references

Acknowledgements

We thank F. Radu for generous help during sample preparation and S. Valencia and K. Carva for fruitful discussions. Financial support by the German Ministry of Education and Research BMBF Grant 05K10PG2 FEMTOSPEX, by the Swedish Research Council (VR), the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreements No. 214810 FANTOMAS and No. 281043 FEMTOSPIN, and the Swedish National Infrastructure for Computing (SNIC) is gratefully acknowledged.

Author information

Authors and Affiliations

Authors

Contributions

A.E., N.P., T.K., K.H. R.M. and C.S. performed the time-resolved experiments; A.E. prepared the samples and analysed the data; M.B. and P.M. performed the calculations; C.S., M.B. and P.M.O. wrote the manuscript. All authors commented on, discussed and improved the manuscript.

Corresponding authors

Correspondence to A. Eschenlohr, M. Battiato or C. Stamm.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Eschenlohr, A., Battiato, M., Maldonado, P. et al. Ultrafast spin transport as key to femtosecond demagnetization. Nature Mater 12, 332–336 (2013). https://doi.org/10.1038/nmat3546

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat3546

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing