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Nanoscale Mapping of Ultrafast Magnetization Dynamics with Femtosecond Lorentz Microscopy

Nara Rubiano da Silva1, Marcel Möller1, Armin Feist1, Henning Ulrichs2, Claus Ropers1, and Sascha Schäfer1,*

  • 1University of Göttingen, IV. Physical Institute, Göttingen 37077, Germany
  • 2University of Göttingen, I. Physical Institute, Göttingen 37077, Germany

  • *sascha.schaefer@phys.uni-goettingen.de
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Phys. Rev. X 8, 031052 – Published 29 August, 2018

DOI: https://doi.org/10.1103/PhysRevX.8.031052

Abstract

Novel time-resolved imaging techniques for the investigation of ultrafast nanoscale magnetization dynamics are indispensable for further developments in light-controlled magnetism. Here, we introduce femtosecond Lorentz microscopy, achieving a spatial resolution below 100 nm and a temporal resolution of 700 fs, which gives access to the transiently excited state of the spin system on femtosecond timescales and its subsequent relaxation dynamics. We demonstrate the capabilities of this technique by spatiotemporally mapping the light-induced demagnetization of a single magnetic vortex structure and quantitatively extracting the evolution of the magnetization field after optical excitation. Tunable electron imaging conditions allow for an optimization of spatial resolution or field sensitivity, enabling future investigations of ultrafast internal dynamics of magnetic topological defects on a 10 nm length scale.

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Popular Summary

Current information storage technologies largely rely on the fast switching of nanometer-scale magnetic domains. An in-depth understanding of transient magnetic states far from equilibrium may further increase the writing and recording speed of this technology as well as its storage density. Currently, however, experimental tools to image the evolution of such magnetic states on nanometer length scales and subpicosecond time scales are only beginning to become available and are often only accessible at large-scale research facilities. Here, we use femtosecond electron pulses to take snapshots of the transient magnetic state of a single permalloy nanostructure.

We strongly perturb the nanostructure by applying a femtosecond near-infrared laser pulse. By stitching together several such snapshots at different times after optical excitation, we construct a nanoscale movie of the magnetic structure showing its evolution over a time span of a few picoseconds. We are able to achieve a spatial resolution better than 100 nm and a temporal resolution of roughly 700 fs.

The simultaneous high spatial and temporal resolutions of our technique, combined with the ability to quantitatively map the magnetization fields, provide a novel experimental platform for future developments of advanced magnetic storage applications.

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Phys. Rev. X 8, 031052– Published 29 August, 2018
  • Received 28 November 2017
  • Revised 28 February 2018
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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