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Regensburg 2019 – scientific programme

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MA: Fachverband Magnetismus

MA 15: Magnetism Poster A

MA 15.56: Poster

Tuesday, April 2, 2019, 10:00–13:00, Poster E

Ultrafast negative thermal expansion driven by spin-disorder in antiferromagnetic Holmium — •Jan-Etienne Pudell1, Alexander von Reppert1, Daniel Schick2, Flavio Zamponi1, Matthias Rössle3, Marc Herzog1, Hartmut Zabel4, and Matias Bargheer1,31Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht- Str. 24-25, 14476 Potsdam, Germany — 2Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany — 3Helmholtz Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin, Germany — 4Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, 44780 Bochum, Germany

We measure the transient strain profile in a nanoscale multilayer system composed of Yttrium, Holmium and Niobium after femtosecond laser excitation using ultrafast X-ray diffraction (UXRD) at a laser-driven Plasma X-ray Source (PXS) setup. The strain propagation through each layer is determined by transient changes of the material-specific Bragg angles. We experimentally derive the exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical penetration depth. Below the Neel temperature of Ho, the optical excitation triggers negative thermal expansion caused by a decrease of the strong magnetostriction in Holmium, which is induced by a quasi-instantaneous contractive stress, and a second contractive stress contribution rising on a 12 ps timescale. These two timescales have recently been measured for the spin-disordering in Ho [Rettig et al, PRL 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar strain pulse with an inverted sign.

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