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MA: Fachverband Magnetismus
MA 52: Poster II
MA 52.37: Poster
Donnerstag, 15. März 2018, 15:00–18:00, Poster C
Spin excitations in antiferromagnetic rare earths drive ultrafast negative thermal expansion — •Jan-Etienne Pudell1, Alexander von Reppert1, Flavio Zamponi1, Matthias Rössle1,2, Hartmut Zabel3, Daniel Schick2, and Matias Bargheer1,2 — 1Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany — 2Helmholtz-Zentrum Berlin, Berlin, Germany — 3Institut für Experimentalphysik , Ruhr Universität Bochum, Bochum, Germany
We present ultrafast x-ray diffraction (UXRD) measurements on a nanolayer system of Holmium (Ho), Yttrium and Niobium layers. We excite the samples by femtosecond light pulses, which instantaneously heat up the electron gas. The coupling of this deposited energy to spin degrees of freedom and to phonons, which simultaneously measured in all constituting layers by x-ray diffraction of 200 femtosecond pulses derived from a laser based plasma source. In the helical antiferromagnetic phase of Ho the energy transferred from the electrons to the spin system leads to a pronounced lattice contraction, whereas heating the phonon system leads to a negative stress component. The sign of the measured ultrafast strain profiles changes upon cooling to the AFM phase, yielding direct evidence of the negative driving stress due to spin excitations. By modeling the generated coherent strain wave in the layers we can derive the spatio-temporal stress profiles generated by the phonon and spin contributions.