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MA: Fachverband Magnetismus
MA 3: Ultrafast Magnetization Effects I
MA 3.2: Vortrag
Montag, 18. März 2024, 10:00–10:15, H 2013
Ultrafast generation of nonthermal magnons in iron: Ab initio parameterized calculations — •Markus Weißenhofer1,2 and Peter M. Oppeneer1 — 1Uppsala University, Uppsala, Sweden — 2Freie Universität Berlin, Berlin, Germany
Ultrafast laser excitation of ferromagnetic metals gives rise to correlated, highly non-equilibrium dynamics of electrons, spins and lattice, which are, however, poorly described by the widely used three-temperature model (3TM). We develop a fully ab initio parameterized out-of-equilibrium theory based on a quantum kinetic approach – termed (N+2) temperature model – that describes magnon occupation dynamics due to electron-magnon scattering [1]. We apply this model to perform quantitative simulations on the ultrafast, laser-induced generation of magnons in iron and demonstrate that on these timescales the magnon distribution is non-thermal: predominantly high-energy magnons are created, while the magnon occupation close to the center of the Brillouin zone even decreases, due to a repopulation towards higher energy states. We show that the 3TM can be derived from our model and compare it with our microscopic calculations. In doing so, we demonstrate that the simple relation between magnetization and temperature computed at equilibrium does not hold in the ultrafast regime and that the 3TM greatly overestimates the demagnetization. Our calculations show that ultrafast generation of non-thermal magnons provides a sizable demagnetization within 200 fs and, thus, emphasize the importance of magnons for ultrafast demagnetization. [1] M.Weißenhofer and P.M. Oppeneer, arXiv:2309.14167
Keywords: Ultrafast demagnetization; Electron-magnon coupling; Magnons excitation; Out-of-equilibrium dynamics