Barre 22-32, 2e étage, salle 201
Matthias Riepp – Institut de Physique et Chimie des Matériaux de Strasbourg et Deutsches Elektronen-Synchrotron DESY, Hamburg.
Abstract
Terahertz (THz) light pulses can be used for an ultrafast coherent manipulation of the magnetization [1,2], which is among the fastest possible ways of writing magnetic information in ferromagnetic thin films [3]. Using time-resolved resonant magnetic scattering at the free-electron laser FLASH beamline BL3 [4], we gained completely new insights to the THz-driven coherent magnetization dynamics on nanometer length scales. We observe ultrafast incoherent demagnetization as well as ultrafast coherent magnetization oscillations that are governed by a time-dependent damping. This damping is determined by the time- and fluence-dependent compensation of the magnetic anisotropy energy barrier, suggesting an upper speed limit for THz-induced magnetization switching. We find that, in the presence of nanometer-sized magnetic domains, the ultrafast coherent magnetization oscillations are associated with a correlated beating of the domain walls. The overall domain structure thereby remains largely unaffected, highlighting the applicability of THz-induced magnetization switching on the nanoscale.
[1] Nature Photonics 5(1), 31–34 (2011)
[2] Physical Review Letters 117(8), 087205 (2016)
[3] Nature 428(6985), 831–833 (2004)
[4] Journal of Synchrotron Radiation 26(3), 700–707 (2019)
