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arXiv · 2404.04980

Element-specific ultrafast lattice dynamics in FePt nanoparticles

Diego Turenne·Igor Vaskivskiy·Klaus Sokolowski-Tinten·Xijie Wang·Alexander H. Reid·Xiaoshe Shen·Ming-Fu Lin·Suji Park·Stephen Weathersby·Michael Kozina·Matthias Hoffmann·Jian Wang·Jakub Sebesta·Yukiko K. Takahashi·Oscar Grånäs·Peter Oppeneer·Hermann A. Dürr
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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.

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Diego Turenne, Igor Vaskivskiy, Klaus Sokolowski-Tinten, Xijie Wang, Alexander H. Reid, Xiaoshe Shen, Ming-Fu Lin, Suji Park, Stephen Weathersby, Michael Kozina, Matthias Hoffmann, Jian Wang, Jakub Sebesta, Yukiko K. Takahashi, Oscar Grånäs, Peter Oppeneer, Hermann A. Dürr. 2024-04-07. Element-specific ultrafast lattice dynamics in FePt nanoparticles. https://arxiv.org/abs/2404.04980

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