Ab initio investigation of laser-induced ultrafast demagnetization of L1$_0$ FePt: Intensity dependence and importance of electron coherence
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| Format: | Preprint |
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2023
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| _version_ | 1866910422211231744 |
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| author | Mrudul, M. S. Oppeneer, Peter M. |
| author_facet | Mrudul, M. S. Oppeneer, Peter M. |
| contents | 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 in TDDFT is a longitudinal magnetization reduction and 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., $ΔM_z \propto E^{2}$. Moreover, the magnetization dynamics happens dominantly at even multiples $nω_0$, ($n = 0, 2, \cdots$) of the pump-laser frequency $ω_0$, whereas odd multiples of $ω_0$ do not contribute. We further investigate the demagnetization in conjunction to the optically-induced change of electron occupations and electron correlations. Correlations within the Kohn-Sham local-density framework are shown to have an appreciable yet distinct effect on the amount of demagnetization depending on the laser intensity. 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2307_11736 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Ab initio investigation of laser-induced ultrafast demagnetization of L1$_0$ FePt: Intensity dependence and importance of electron coherence Mrudul, M. S. Oppeneer, Peter M. Materials Science 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 in TDDFT is a longitudinal magnetization reduction and 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., $ΔM_z \propto E^{2}$. Moreover, the magnetization dynamics happens dominantly at even multiples $nω_0$, ($n = 0, 2, \cdots$) of the pump-laser frequency $ω_0$, whereas odd multiples of $ω_0$ do not contribute. We further investigate the demagnetization in conjunction to the optically-induced change of electron occupations and electron correlations. Correlations within the Kohn-Sham local-density framework are shown to have an appreciable yet distinct effect on the amount of demagnetization depending on the laser intensity. 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. |
| title | Ab initio investigation of laser-induced ultrafast demagnetization of L1$_0$ FePt: Intensity dependence and importance of electron coherence |
| topic | Materials Science |
| url | https://arxiv.org/abs/2307.11736 |