Phys. Rev. X 2, 011005 (2012) [7 pages]

Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions

Popular Summary: Femtomagnetism explores how fast magnetic materials can magnetize or demagnetize—timescales that depend on the coupled motions of charges, spins, atoms, and phonons in materials. While still relatively young, this research area is vibrant, thanks in no small measure to laser-based magneto-optical techniques, which are used to induce, and probe, ultrafast (de)magnetization dynamics. Ultrafast x-ray pulses can probe element-specific dynamics, providing rich new information not accessible using visible light. However, until very recently, only large-scale synchrotron and x-ray free-electron laser facilities could view element-specific dynamics in magnetic materials, with time resolutions of about 100 femtoseconds. Is there another route to femtomagnetism that is small scale, more accessible, and capable of capturing the fastest dynamics in magnetic materials? In this work that uses broad-bandwidth ultrafast x-rays from a tabletop high-harmonic laser source to probe magnetic materials, we demonstrate unequivocally that the answer is “yes.”

In a recent paper, we showed that ultrafast high harmonics with photon energies in the range of 40 to 70 eV can probe how fast the magnetization in a ferromagnetic material can be destroyed. However, two important issues remained open. First, were the measured changes in the intensity of the reflected harmonic beams due only to a change in the magnetic alignment of the material after its interaction with a laser, or did the signal also contain contributions due to excited electrons created by the laser? Such nonmagnetic artifacts are known to influence all time-resolved magnetic probe techniques to date. Second, the time resolution was limited by the experimental geometry, so the limiting speed of demagnetization was not known. In the present work, our team addressed both questions conclusively to show that the intensity of the reflected high-harmonic light is only sensitive to the magnetic (spin) state of the material, with no contributions from excited charges or phonons. We have also been able to measure how fast the magnetization in a material can be destroyed, with a temporal resolution of less than 20 femtoseconds, and with elemental specificity.

This work paves the way to the most accurate measurements of magnetic dynamics and interactions in complex materials.

Abstract

References

Citing Articles (2)

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Chan La-O-Vorakiat^*, Emrah Turgut, Carson A. Teale, Henry C. Kapteyn, and Margaret M. Murnane
Department of Physics and JILA, and NSF Engineering Research Center in Extreme Ultraviolet Science and Technology, University of Colorado and NIST, Boulder, Colorado 80309, USA

Stefan Mathias^† and Martin Aeschlimann
University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern, Germany

Claus M. Schneider
Peter Grünberg Institute, PGI-6, Research Center Jülich, 52425, Jülich, Germany

Justin M. Shaw, Hans T. Nembach, and T. J. Silva
Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA

Received 26 October 2011; published 23 January 2012

See accompanying Physics Viewpoint

Ultrashort pulses of extreme ultraviolet light from high-harmonic generation are a new tool for probing coupled charge, spin, and phonon dynamics with element specificity, attosecond pump-probe synchronization, and time resolution of a few femtoseconds in a tabletop apparatus. In this paper, we address an important question in magneto-optics that has implications for understanding magnetism on the fastest time scales: Is the signal from the transverse magneto-optical Kerr effect at the M_2,3 edges of a magnetic material purely magnetic or is it perturbed by nonmagnetic artifacts? Our measurements demonstrate conclusively that transverse magneto-optical Kerr measurements at the M_2,3 edges sensitively probe the magnetic state, with almost negligible contributions from the transient variation of the refractive index by the nonequilibrium hot-electron distribution. In addition, we compare pump-probe demagnetization dynamics measured by both high harmonics and conventional visible-wavelength magneto-optics and find that the measured demagnetization times are in agreement.

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevX.2.011005

DOI:

10.1103/PhysRevX.2.011005

PACS:

75.78.Jp

Subject Areas:

Magnetism, Optics

^*Corresponding author.

Chan.La-o-vorakiat@Colorado.EDU

^†Corresponding author.

smathias@physik.uni-kl.de

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Phys. Rev. X 2, 011005 (2012) [7 pages]

Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions