Letter | Published:

Paradigm of the time-resolved magneto-optical Kerr effect for femtosecond magnetism

Nature Physics volume 5, pages 499502 (2009) | Download Citation


The magneto-optical Kerr effect (MOKE) is a powerful tool for studying changes in the magnetization of ferromagnetic materials. It works by measuring changes in the polarization of reflected light. However, because the conventional theoretical basis for interpreting a MOKE signal assumes measurement with continuous-wave light1,2, its use for understanding high-speed magnetization dynamics of a material probed with femtosecond optical pulses3,4 has been controversial5,6,7,8,9,10. Here we establish a new paradigm for interpreting time-resolved MOKE measurements, through a first-principles investigation of ferromagnetic nickel. We show that the time-resolved optical and magnetic responses energetically follow their respective optical and magneto-optical susceptibilities. As a result, the one-to-one correspondence between them sensitively depends on the incident photon energy. In nickel, for photon energies below 2 eV the magnetic response is faithfully reflected in the optical response, but above 2 eV they decouple. By constructing a phase-sensitive polarization versus magnetization plot, we find that for short pulses the magnetic signals are delayed by 10 fs with respect to the optical signals. For longer pulses, the delay shortens and the behaviour approaches the continuous-wave response. This finally resolves the long-standing dispute over the interpretation in the time-resolved MOKE measurements and lays a solid foundation for understanding femtomagnetism3,4.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    Theory of the Faraday and Kerr effects in ferromagnetics. Phys. Rev. 97, 334–345 (1955).

  2. 2.

    & Magneto-optic Kerr effects in gadolinium. Phys. Rev. B 8, 1239–1255 (1973).

  3. 3.

    , , & Ultrafast spin dynamics in ferromagnetic nickel. Phys. Rev. Lett. 76, 4250–4253 (1996).

  4. 4.

    , , & Laser-induced ultrafast demagnetization: Femtomagnetism, a new frontier? Topics Appl. Phys. 83, 245–289 (2002).

  5. 5.

    , , & Ultrafast magneto-optics in nickel: Magnetism or optics? Phys. Rev. Lett. 85, 844–847 (2000).

  6. 6.

    , & Magneto-optics in the ultrafast regime: Thermalization of spin populations in ferromagnetic films. Phys. Rev. Lett. 89, 017401 (2002).

  7. 7.

    , , & Femtosecond spectrotemporal magneto-optics. Phys. Rev. Lett. 93, 077401 (2004).

  8. 8.

    et al. Investigation of ultrafast demagnetization and cubic optical nonlinearity of Ni in the polar geometry. J. Appl. Phys. 95, 7441–7443 (2004).

  9. 9.

    , , , & Femtosecond dynamics of Co thin films on Si support. Solid State Commun. 129, 227–231 (2004).

  10. 10.

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

  11. 11.

    et al. All-optical magnetic recording with circularly polarized light. Phys. Rev. Lett. 99, 047601 (2007).

  12. 12.

    & Laser-induced ultrafast demagnetization in ferromagnetic metals. Phys. Rev. Lett. 85, 3025–3028 (2000).

  13. 13.

    & First-principles study of ultrafast magneto-optical switching in NiO. Phys. Rev. B 76, 014418 (2007).

  14. 14.

    , , & All-optical subpicosecond magnetic switching in NiO(001). Phys. Rev. Lett. 92, 227402 (2004).

  15. 15.

    , , & Nonequilibrium magnetization dynamics of nickel. Phys. Rev. Lett. 78, 4861–4864 (1997); erratum 79, 960–960 (1997).

  16. 16.

    , & Time-resolved magnetization-induced second-harmonic generation from the Ni(110) surface. Phys. Rev. B 61, 14716–14722 (2000).

  17. 17.

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

  18. 18.

    et al. Laser-induced magnetization dynamics of lanthanide-doped permalloy thin films. Phys. Rev. Lett. 102, 117201 (2009).

  19. 19.

    , & Transient inverse Faraday effect and ultrafast optical switching of magnetization. Phys. Rev. B 78, 134430 (2008).

  20. 20.

    & Ultrafast spin dynamics in nickel. Phys. Rev. B 58, R5920–R5923 (1998).

  21. 21.

    & Ultrafast demagnetization in Ni: Theory of magneto-optics for non-equilibrium electron distributions. J. Phys. Condens. Matter 16, 5519–5530 (2004).

  22. 22.

    & Formally linear response theory of pump–probe experiments. Phys. Rev. B 71, 165108 (2005).

  23. 23.

    Laser-induced orbital and spin excitations in ferromagnets: Insights from a two-level system. Phys. Rev. Lett. 101, 187203 (2008).

  24. 24.

    & Total angular momentum conservation in laser-induced femtosecond magnetism. Phys. Rev. B 78, 052407 (2008).

  25. 25.

    , , , & Understanding laser-induced ultrafast magnetization in ferromagnets: First-principles investigation. J. Appl. Phys. 103, 07B113 (2008).

  26. 26.

    & Parallel block-tridiagonalization of real symmetric matrices. J. Parallel. Distrib. Comput. 68, 703–715 (2008).

  27. 27.

    , , , & WIEN2k, An Augmented Plane Wave + Local Orbitals Program for Calculating Crystal Properties (Karlheinz Schwarz, Techn. Universität Wien, 2001).

  28. 28.

    et al. Ultrafast magneto-optical response of iron thin films. Phys. Rev. B 65, 104429 (2002).

  29. 29.

    et al. Photoinduced spin dynamics in La0.6Sr0.4MnO3 observed by time-resolved magneto-optical Kerr spectroscopy. Phys. Rev. B 68, 180407(R) (2003).

  30. 30.

    Femtosecond magneto-optical processes in metals. C. R. Acad. Sci. Paris, t. Sèrie IV 2, 1483–1504 (2001).

Download references


This work was supported by the US Department of Energy under contract No DE-FG02-06ER46304 and US Army Research Office under contract W911NF-04-1-0383, and was also supported by a Promising Scholars grant from Indiana State University. In addition, we acknowledge part of the work as done on Indiana State University’s high performance computers. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under contract No DE-AC02-05CH11231. W.H. and G.L. acknowledge support from Priority Programmes 1133 and 1153 of the German Research Foundation. Initial studies used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the US Department of Energy under contract No DE-AC02-06CH11357.

Author information


  1. Department of Physics, Indiana State University, Terre Haute, Indiana 47809, USA

    • G. P. Zhang
  2. Department of Physics, Kaiserslautern University of Technology and Research Center OPTIMAS, Box 3049, D-67653 Kaiserslautern, Germany

    • W. Hübner
    •  & Georgios Lefkidis
  3. Department of Physics and Center for Instruction, Research and Technology, Indiana State University, Terre Haute, Indiana 47809, USA

    • Yihua Bai
  4. Office of the Chancellor and Center for Nanoscience, Departments of Chemistry, Biochemistry and Physics & Astronomy, University of Missouri-St. Louis, St. Louis, Missouri 63121, USA

    • Thomas F. George


  1. Search for G. P. Zhang in:

  2. Search for W. Hübner in:

  3. Search for Georgios Lefkidis in:

  4. Search for Yihua Bai in:

  5. Search for Thomas F. George in:


G.P.Z. drafted the paper, and W.H., G.L., Y.B. and T.F.G. modified it. G.P.Z. computed the results, and G.P.Z., W.H. and G.L. analysed the data. Y.B. implemented the parallelization of the source code.

Corresponding author

Correspondence to G. P. Zhang.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information

About this article

Publication history






Further reading