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Condensed Matter > Materials Science
Title: Element-specific ultrafast lattice dynamics in FePt nanoparticles
(Submitted on 7 Apr 2024 (v1), last revised 13 Apr 2024 (this version, v2))
Abstract: Light-matter interaction at the nanoscale in magnetic alloys and heterostructures is a topic of intense research in view of potential applications in high-density magnetic recording. While the element-specific dynamics of electron spins is directly accessible to resonant x-ray pulses with femtosecond time structure, the possible element-specific atomic motion remains largely unexplored. We use ultrafast electron diffraction to probe the temporal evolution of lattice Bragg peaks of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. The diffraction interference between Fe and Pt sublattices enables us to demonstrate that the Fe mean-square vibration amplitudes are significantly larger that those of Pt as expected from their different atomic mass. Both are found to increase as energy is transferred from the laser-excited electrons to the lattice. Contrary to this intuitive behavior, we observe a laser-induced lattice expansion that is larger for Pt than for Fe atoms during the first picosecond after laser excitation. This effect points to the strain-wave driven lattice expansion with the longitudinal acoustic Pt motion dominating that of Fe.
Submission history
From: Hermann Durr [view email][v1] Sun, 7 Apr 2024 14:52:17 GMT (2733kb)
[v2] Sat, 13 Apr 2024 05:35:00 GMT (2996kb)
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