Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Internal Online Seminar
Chair: Martin Wolf

Thursday, January 21, 2021, 2:00 pm
Oliver Sandig
Laser Induced Magnetization Dynamics of Ferromagnets: Investigated by X-TR-PEEM and TR-MOKE
The first part of the talk focusses on a microscopic investigation of the changes in the magnetic domain structure of ultrathin Co films after direct excitation by single ultrashort laser pulses with a central wavelength of 800 nm. Photoelectron emission microscopy in combination with x-ray magnetic circular dichroism in the resonant absorption of soft x rays was used to image the changes of the magnetic domain structure of a 3 ML thick Co layer in an epitaxial Co/Cu/Ni trilayer on a Cu(001) single-crystal substrate. It will additionally be shown that a relatively small enhancement of the sample base temperature by 40 K is sufficient to lower the threshold of laser fluence for domain wall motion by about factor two. Quantitatively, the domain wall motion appears similar to thermal domain wall fluctuations; however, pure thermal activation of domain wall motion induced by the laser pulse is not a sufficient explanation. Still, the motion is likely triggered by a laser-induced depinning of domain walls. In the second part of the talk, the development of a setup to measure the time resolved magneto-optic effect (TR-MOKE) will be detailed. Starting from scratch, key steps in the realization of the set-up were: 1. The consideration of the required fluence and the spot size of the laser 2. The estimation of time zero by way of a self-made autocorrelator After that, example measurements such as the demagnetization of a Co/Pt multilayer and the precession of a thin Ni80Fe20 film show the performance of the new setup.

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