# Dresden 2020 – wissenschaftliches Programm

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# SYAS: Symposium Attosecond and coherent spins: New frontiers

## SYAS 1: Attosecond and Coherent Spins: New Frontiers

### SYAS 1.1: Hauptvortrag

### Montag, 16. März 2020, 15:00–15:30, HSZ 02

**Ultrafast Coherent Spin-Lattice Interactions in Ferromagnets** — •Steven L. Johnson — Institute for Quantum Electronic, Eidgenossische Technische Hochschule, Zürich, Swiitzerland — SwissFEL, Paul Scherrer Institut, Villigen, Switzerland

The interaction of spins in a ferromagnet with the underlying lattice during the process of ultrafast demagentization has for some time been shrouded in mystery, and is intimately connected to the fundamental question of exactly how angular momentum is conserved in such processes. The original Einstein de Haas experiment of the early 20th century showed dramatically that the angular momentum of the electron spins responsible for ferromagnetism is the same angular momentum that we know well from classical mechanics. In this talk I explore how the Einstein de Haas effect can manifest in the time domain on ultrafast time scales in response to ultrafast demagnetization of a 3d ferromagnet. In a thin film geometry, the transfer of angular momentum to the lattice is accomplished by a transient mechanical torque that launches a small but measurable transverse displacement wave into the film. I also describe an experiment using ultrafast x-ray diffraction performed at the LCLS free electron laser that observed these dynamics. Based on this we make a first estimate of the magnitude and time scale of angular momentum transfer to the lattice in the first few hundred femtoseconds after ultrafast demagnetization. I also discuss future directions in this research to further investigate the underlying mechanisms.