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
Access options
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Beaurepaire, E., Merle, J-C., Daunois, A. & Bigot, J-Y. Ultrafast spin dynamics in ferromagnetic nickel. Phys. Rev. Lett. 76, 4250–4253 (1996).
Carpene, E. et al. Dynamics of electron–magnon interaction and ultrafast demagnetization in thin iron films. Phys. Rev. B 78, 174422 (2008).
Krauß, M. et al. Ultrafast demagnetization of ferromagnetic transition metals: The role of the Coulomb interaction. Phys. Rev. B 80, 180407 (2009).
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).
Bigot, J-Y., Vomir, M. & Beaurepaire, E. Coherent ultrafast magnetism induced by femtosecond laser pulses. Nature Phys. 5, 515–520 (2009).
Koopmans, B. et al. Explaining the paradoxical diversity of ultrafast laser-induced demagnetization. Nature Mater. 9, 259–265 (2010).
Kirilyuk, A., Kimel, A. V. & Rasing, Th. Ultrafast optical manipulation of magnetic order. Rev. Mod. Phys. 82, 2731–2784 (2010).
Battiato, M., Carva, K. & Oppeneer, P. M. Superdiffusive spin transport as a mechanism of ultrafast demagnetization. Phys. Rev. Lett. 105, 027203 (2010).
Stamm, C. et al. Femtosecond modification of electron localization and transfer of angular momentum in nickel. Nature Mater. 6, 740–743 (2007).
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).
Windt, D. L. IMD-Software for modelling the optical properties of multilayer films. Comput. Phys. 12, 360–370 (1998).
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).
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).
Melnikov, A. et al. Ultrafast transport of laser-excited spin-polarized carriers in Au/Fe/MgO(001). Phys. Rev. Lett. 107, 076601 (2011).
Battiato, M., Carva, K. & Oppeneer, P. M. Theory of laser-induced ultrafast superdiffusive spin transport in layered heterostructures. Phys. Rev. B 86, 024404 (2012).
Stöhr, J. & Siegmann, H. C. Magnetism: From Fundamentals to Nanoscale Dynamics (Springer, 2006).
Carva, K., Battiatio, M. & Oppeneer, P. M. Is the controversy over femtosecond magneto-optics really solved? Nature Phys. 7, 665–666 (2011).
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).
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).
Neubrand, A. & Hess, P. Laser generation and detection of surface acoustic waves: Elastic properties of surface layers. J. Appl. Phys. 71, 227–238 (1992).
Djordjevic, M. et al. Comprehensive view on ultrafast dynamics of ferromagnetic films. Phys. Status Solidi 3, 1347–1358 (2006).
Wang, X. et al. Temperature dependence of electron–phonon thermalization and its correlation to ultrafast magnetism. Phys. Rev. B 81, 220301 (2010).
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).
Khan, S., Holldack, K., Kachel, T., Mitzner, R. & Quast, T, T. Femtosecond undulator radiation from sliced electron bunches. Phys. Rev. Lett. 97, 074801 (2006).
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).
Carra, P., Thole, B. T., Altarelli, M. & Wang, X. X-ray circular dichroism and local magnetic fields. Phys. Rev. Lett. 70, 694–697 (1993).
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).
Zhukov, V. P., Chulkov, E. V. & Echenique, P. M. GW+T theory of excited electron lifetimes in metals. Phys. Rev. B 72, 155109 (2005).
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
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
Ethics declarations
Competing interests
The authors declare no competing financial interests.
Rights 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
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/nmat3546
This article is cited by
-
Ultrafast magnetization enhancement and spin current injection in magnetic multilayers by exciting the nonmagnetic metal
Science China Physics, Mechanics & Astronomy (2023)
-
Lost magnetism pinned on atomic rotations
Nature (2022)
-
Polarized phonons carry angular momentum in ultrafast demagnetization
Nature (2022)
-
Exchange scaling of ultrafast angular momentum transfer in 4f antiferromagnets
Nature Materials (2022)
-
Mechanism of femtosecond laser induced ultrafast demagnetization in ultrathin film magnetic multilayers
Journal of Materials Science (2022)