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We report the demonstration of picosecond Fresnel imaging with an ultrafast transmission electron microscope (UEM). By operating with a low instrument repetition rate (5 kHz) and without objective-lens excitation, the picosecond demagnetization of an FePt film, via in situ, femtosecond laser excitation, is directly imaged. The dynamics are quantified and monitored as a time-dependent change in the degree of electron coherence within the magnetic domain walls. The relative coherence of conventional (thermionic) Fresnel transmission electron microscopy is also directly compared to that of Fresnel UEM through the domain-wall size. Further, the robustness and reversibility of the domain-wall dynamics are illustrated by repeating the picosecond image scans at defocus values having the same magnitude but different signs (e.g., +25 mm vs. −25 mm). Control experiments and approaches to identifying and isolating systematic errors and sources of artifacts are also described. This work, and continued future developments also described here, opens the way to direct correlation of transient structure, morphology, and magnetic dynamics in magnetic thin films and spintronic devices.
Bibliographical noteFunding Information:
This work was supported partially by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013. This work was partially supported by C-SPIN, one of six STARnet Centers, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA. Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the UMN MRSEC program under Award Numbers DMR-0819885 and DMR-1420013. Part of this work was carried out in the College of Science and Engineering Institute for Rock Magnetism, University of Minnesota, which is made possible in part through the Instrumentation and Facilities program of the NSF Earth Science Division. Additional support was provided by the Arnold and Mabel Beckman Foundation through a Beckman Young Investigator Award (D.J.F.)
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Reporting period for MRSEC
- Period 4