Dresden 2020 – scientific programme

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MA: Fachverband Magnetismus

MA 2: Ultrafast Magnetization I

MA 2.4: Talk

Monday, March 16, 2020, 10:15–10:30, HSZ 101

Photon energy dependent fs-demagnetization dynamics of thin Ni films — •Martin Stiehl, Jonas Hoefer, Sebastian Weber, Sanjay Ashok, Moritz Hofherr, Ute Bierbrauer, Benjamin Stadtmüller, Bärbel Rethfeld, and Martin Aeschlimann — Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern, Germany

After the first observation of the ultrafast demagnetization process, a huge experimental and theoretical effort was devoted to reveal the microscopic mechanism governing the ultrafast optically induced loss of magnetic order in ferromagnetic materials. Almost all experimental fs-demagnetization studies so far employed fs light pulses of 1.55 eV to trigger the magnetization-dynamics. Hence, the role of the photon energy of the exciting light pulse has not been thoroughly investigated so far. Therefore, we have implemented an all-optical time-resolved MOKE setup with variable pump photon energy in the range of 1.55 to 3.10 eV. As prototypical system, we investigated the ultrafast demagnetization dynamics of thin Ni films on insulating and conducting substrates for various excitation photon energies. The characteristic parameters of the demagnetization process, i.e., the demagnetization time and the induced magnetization in the conducting substrate, are compared with simulations applying Boltzmann collision integrals including the density of states of Nickel to describing the non-equilibrium dynamics of the spin-carrying excited electrons.