Regensburg 2019 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 2: Ultrafast magnetization effects and magnetization dynamics

MA 2.9: Vortrag

Montag, 1. April 2019, 11:45–12:00, H37

Uncovering the magnetic origin of the contractive stress in laser-excited FePt by ultrafast X-ray diffraction — •Alexander von Reppert1, Jan-Etienne Pudell1, Steffen Zeuschner1,2, Lisa Willig1, Matthias Rössle2, Marc Herzog1, Fabian Ganss3, Olav Hellwig3,4, and Matias Bargheer1,21Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany — 2Helmholtz-Zentrum Berlin, Berlin, Germany — 3Institut für Physik, Technische Universität Chemnitz, Chemnitz, Germany — 4Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

Here we present a systematic study of the previously observed contraction of laser-excited granular FePt by ultrafast X-ray diffraction. Double-pulse excitation experiments show that the contractive stress is suppressed when the FePt is transiently demagnetized and it recovers as the magnetization reestablishes. The saturation of the observed contraction in a fluence study and the timescale for the remagnetization in time-resolved MOKE measurements corroborate this finding. The comparison between the lattice response of continuous and granular FePt films shows that the in-plane geometry of the sample is crucial for the observed lattice dynamics, although we can exclude the anisotropic phonon and electron expansion coefficients as the only origin of the out-of-plane contraction. In this work we demonstrate how double-pulse excitation experiments can disentangle competing mechanisms at phase transitions, which are difficult to access.

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