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4D Lorentz Electron Microscopy Imaging: Magnetic Domain Wall Nucleation, Reversal, and Wave Velocity

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Hyun Soon Park, J. Spencer Baskin and Ahmed H. Zewail*

Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125

Nano Lett., 2010, 10 (9), pp 3796–3803

DOI: 10.1021/nl102861e

Publication Date (Web): August 25, 2010

* To whom correspondence should be addressed, zewail@caltech.edu.

Section:

Magnetic Phenomena

Abstract

Magnetization reversal is an important topic of research in the fields of both basic and applied ferromagnetism. For the study of magnetization reversal dynamics and magnetic domain wall (DW) motion in ferromagnetic thin films, imaging techniques are indispensable. Here, we report 4D imaging of DWs by the out-of-focus Fresnel method in Lorentz ultrafast electron microscopy (UEM), with in situ spatial and temporal resolutions. The temporal change in magnetization, as revealed by changes in image contrast, is clocked using an impulsive optical field to produce structural deformation of the specimen, thus modulating magnetic field components in the specimen plane. Directly visualized are DW nucleation and subsequent annihilation and oscillatory reappearance (periods of 32 and 45 ns) in nickel films on two different substrates. For the case of Ni films on a Ti/Si₃N₄ substrate, under conditions of minimum residual external magnetic field, the oscillation is associated with a unique traveling wave train of periodic magnetization reversal. The velocity of DW propagation in this wave train is measured to be 172 m/s with a wavelength of 7.8 μm. The success of this study demonstrates the promise of Lorentz UEM for real-space imaging of spin switching, ferromagnetic resonance, and laser-induced demagnetization in ferromagnetic nanostructures.

Keywords:

4D imaging; magnetic domain dynamics; ultrafast electron microscopy; ferromagnetic materials

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Nanomusical Systems Visualized and Controlled in 4D Electron Microscopy
J. Spencer Baskin, Hyun Soon Park, and Ahmed H. Zewail
Nano Letters2011 11 (5), 2183-2191
- Nanomusical Systems Visualized and Controlled in 4D Electron Microscopy
  J. Spencer Baskin, Hyun Soon Park, and Ahmed H. Zewail
  Nano Letters2011 11 (5), 2183-2191
  Nanomusical systems, nanoharp and nanopiano, fabricated as arrays of cantilevers by focused ion beam milling of a layered Ni/Ti/Si3N4 thin film, have been investigated in 4D electron microscopy. With the imaging and selective femtosecond and nanosecond ...
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