Physics - Magnetism - Element-selective imaging of magnetic material properties in the realm of femtoseconds and nanometers.
Final Report Abstract
The overall goal of this project was to advance tabletop extreme ultraviolet (EUV) techniques that can capture element-selective magnetization dynamics in complex materials on fundamental time and length scales in the realm of nanometers and femtoseconds. Thus, it was possible to present evidence of giant, quasi-ballistic spin currents generated during laser-driven demagnetization in GMR-type multilayer structures. By exciting a magnetic trilayer (Fe/Ru/Ni) with an ultrafast laser pulse, and then probing the magnetization of the individual nanometer thin Ni and Fe layers using HHG, it was found that optically-induced demagnetization can undergo a surprising transient enhancement of the magnetization. Femtosecond spin dynamics of the individual Ni and Fe layers, which are interlayer exchange coupled via the Ru spacer, depends on the relative alignment of their initial magnetization. This data also conclusively showed that both non-local spin-currents and localized spin-flips contribute to the optically induced demagnetization process, the ratio of which can be controlled by the layer structure and composition, which is important in the light of designing material properties and functionality. Due to technical difficulties in implementing element-specific (dynamic) magnetic imaging on the tabletop and the coincidental emergence of the intriguing possibility to generate circularly polarized high harmonic tabletop light, it was decided to deviate from the original concept and to pursue the development of circular HHG capabilities. In this pioneering work, the first phase-matched circularly polarized HHG was demonstrated, and it was used for x-ray magnetic circular dichroism (XMCD) measurements of the 3d transition metal ferromagnets as well as the 4f rare earth magnets in the EUV and soft x-ray region. A photon flux comparable to the linearly polarized HHG sources was produced, which represents a critical advance that will facilitate to develop the element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with high spatial and temporal resolution, using a tabletop setup. Furthermore, these results not only demonstrate the universal nature of generating circularly polarized high harmonics by polarization-controlled wavelength mixing, but also point towards the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the EUV and soft x-ray region by controlling the driving laser waveform. Consequently, developing all of these capabilities will not only allow for deepening our understanding of fundamental principles behind light-matter interactions, but also to exert precise control over matter, as the frequency and shape of the electric light field can be tuned to respective resonances, i.e. terahertz to near infrared radiation for phonons/magnons and visible to x-rays for electrons/spins.
Publications
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“Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current”, Nature Communications 3, 1037 (2012)
D. Rudolf, C. La-O-Vorakiat, M. Battiato, R. Adam, J. M. Shaw, E. Turgut, P. Maldonado, S. Mathias, P. Grychtol, H. T. Nembach, T. J. Silva, M. Aeschlimann, H. C. Kapteyn, M. M. Murnane, C. M. Schneider, and P. M. Oppeneer
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"Reply to “Comment on ‘Ultrafast demagnetization measurements using extreme ultraviolet light: Comparison of electronic and magnetic contributions’", Physical Review X 3, 038002 (2013)
E. Turgut, P. Grychtol, C. La-O-Vorakiat, D. E. Adams, H. C. Kapteyn, M. M. Murnane, S. Mathias, M. Aeschlimann, C. M. Schneider, J. M. Shaw, H. T. Nembach and T. J. Silva
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“Controlling the competition between optically induced ultrafast spin-flip scattering and spin transport in magnetic multilayers,” Physical Review Letters 110, 197201 (2013)
E. Turgut, C. La-O-Vorakiat, J. Shaw, P. Grychtol, H. Nembach, D. Rudolf, R. Adam, M. Aeschlimann, C. M. Schneider, T. J. Silva, M. M. Murnane, H. C. Kapteyn, and S. Mathias
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“Ultrafast element-specific magnetization dynamics of complex magnetic materials on a table-top”, Journal of Electron Spectroscopy and Related Phenomena 189, 164 (2013)
S. Mathias, C. La-O-Vorakiat, J. Shaw, E. Turgut, P. Grychtol, R. Adam, D. Rudolf, H. Nembach, T. J. Silva, M. Aeschlimann, C. M. Schneider, H. C. Kapteyn and M. M. Murnane.
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“Femtosecond-laser-induced modifications in Co/Pt multilayers studied with tabletop resonant magnetic scattering“, EPL 109, 17001 (2015)
C. Weier, R. Adam, D. Rudolf, R. Frömter, P. Grychtol, G. Winkler, A. Kobs, H. P. Oepen, H. C. Kapteyn, M. M. Murnane and C. M. Schneider
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“Generation of bright phase-matched circularly-polarized extreme ultraviolet high harmonics”, Nature Photonics 9, 99 (2015)
O. Kfir, P. Grychtol, E. Turgut, R. Knut, D. Zusin, D. & T. Popmintchev, H. Nembach, J. Shaw, A. Fleischer, H. Kapteyn, M. Murnane and O. Cohen
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“Noncollinear generation of angularly isolated circularly polarized high harmonics”, Nature Photonics 9, 743 (2015)
D. Hickstein, F. Dollar, P. Grychtol, J. Ellis, C. Gentry, D. Zusin R. Knut, J. Shaw, T. Fan, K. Dorney, H. Kapteyn, M. Murnane, and C. Durfee
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“Observation of photoelectron distributions resulting from strong field ionization from two-color circularly polarized laser fields using tomographic methods”, PRA 91, 031402(R) (2015)
C. Mancuso, D. Hickstein, P. Grychtol, R. Knut, O. Kfir, F. Dollar, D. Zusin, M. Gopalakrishnan, C. Gentry, E. Turgut, J. Ellis, A. Fleischer, O. Cohen, H. Kapteyn and M. Murnane
