Berlin 2024 – scientific programme

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MA: Fachverband Magnetismus

MA 3: Ultrafast Magnetization Effects I

MA 3.7: Talk

Monday, March 18, 2024, 11:30–11:45, H 2013

Ab initio investigation of laser-induced ultrafast demagnetization of L10 FePt: Intensity dependence and importance of electron coherence — •Mrudul Muraleedharan S. and Peter M. Oppeneer — Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

We theoretically investigate the optically-induced demagnetization of ferromagnetic FePt using the time-dependent density functional theory (TDDFT). We compare the demagnetization mechanism in the perturbative and nonperturbative limits of light-matter interaction and show how the underlying mechanism of the ultrafast demagnetization depends on the driving laser intensity. Our calculations show that the femtosecond demagnetization results from a nonlinear optomagnetic effect akin to the inverse Faraday effect. The demagnetization scales quadratically with the electric field E in the perturbative limit, i.e., Δ M_z ∝ E². Moreover, the magnetization dynamics happens dominantly at even multiples nω₀, (n = 0, 2, ⋯) of the pump-laser frequency ω₀. We further investigate the demagnetization in conjunction to the optically-induced change of electron occupations and electron correlations. Comparing the ab initio computed demagnetizations with those calculated from spin occupations, we show that electronic coherence plays a dominant role in the demagnetization process, whereas interpretations based on the time-dependent occupation numbers poorly describe the ultrafast demagnetization.

Keywords: Ultrafast Demagnetization; TDDFT; FePt