Seminar Series - Ultrafast x-ray diffraction studies of energy transport and phase transitions

12. 3. 2024 10:00 

CEITEC VUT, Purkyňova 123, Brno-Královo Pole, large meeting room S.02 

Prof. Dr. Matias Bargheer
Institute of Physics and Astronomy, University of Potsdam 

We investigate fundamental microscopic processes contributing to energy transport and phase-transitions via the direct material-specific measurement of transient lattice strain by Ultrafast X-ray Diffraction (UXRD) [1]. In thin-film heterostructures, UXRD reveals unconventional forms of energy transport, e.g. heat transport without heating[2] and the dominance of phonon heat transport in the noble metal Au[3]. The direct access to quasi-static strain as a measure of energy density and strain waves reveals how ultrafast demagnetization by heating and magnetoacoustics induce magnetization dynamics[4].

This presentation will emphasize the analysis of the speed limits for the antiferromagnetic-ferromagnetic (AFM-FM) phase transition in FeRh thin films[5] and nanostructures[6]. We identify an intrinsic 8 ps timescale for the light-induced nucleation of ferromagnetic (FM) domains and show that it is not the speed of sound which limits the AFM-FM transition. In regions that are not directly excited by light, the timescale is even slower. In is context, plasmonic effects in nanostructures can speed up the transition again.

[1] M. Mattern, et al.,”Concepts and use cases for picosecond ultrasonics with x-rays”, Photoacoustics 31, 100503 (2023).

[2] J. Pudell, et al., Advanced Functional Materials, “Heat transport without heating”, 30, 2004555 (2020).

[3] M. Herzog, et al., Adv. Funct. Mater., “Phonon-dominated energy transport in purely metallic heterostructures”, 32, 2206179 (2022).

[4] J. Jarecki et al., “Controlling effective field contributions to laser-induced magnetization precession byheterostructure design”, arXiv:2311.03158

[5] M. Mattern, et al.,” Speed limits of the laser-induced phase transition in FeRh”, arXiv:2305.02094

[6] M. Mattern, et al., “Accelerating the laser-induced phase transition in nanostructured FeRh via plasmonic absorption”, arXiv:2309.12683