Femtosecond signatures of optically induced magnons before ultrafast demagnetization

Femtosecond signatures of optically induced magnons before ultrafast demagnetization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Femtosecond signatures of optically induced magnons before ultrafast demagnetization Reza Rouzegar, Oliver Franke, Gal Lemut, Oliver Gueckstock, Junwei Tong, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7456026/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Optically induced demagnetization of 3d metallic ferromagnets proceeds as fast as ~100 fs and is a crucial prerequisite for spintronic applications, such as ultrafast magnetization switching and spin transport. On the 100 fs time scale, the magnetization dynamics is widely understood in the context of temperature models considering energy transfers between conduction electrons, magnons and crystal lattice. However, on even faster time scales, the flow of both angular momentum and energy between these subsystems has so far not been studied. Here, we measure ultrafast demagnetization by ultrabroadband THz-emission spectroscopy. We find that the rate of change of the magnetization does not rise instantaneously, but on a time scale shorter than 10 fs. In the framework of a general model of the three interacting subsystems, this rise is a signature that a transfer of angular momentum from magnons to conduction electrons proceeds in less than 10 fs, before substantial demagnetization has happened. We further conclude that most of the spin dissipated by the crystal lattice is transferred via magnon-lattice rather than electron-lattice interaction. Our results show that the limiting speed of magnetization dynamics is not quenching of magnetic order and harnessing the earliest magnon dynamics could be a new route towards even faster spintronics. Physical sciences/Physics/Condensed-matter physics/Ferromagnetism Physical sciences/Physics/Condensed-matter physics/Magnetic properties and materials Physical sciences/Physics/Condensed-matter physics/Spintronics Full Text Additional Declarations There is NO Competing Interest. Supplementary Files MagnongenerationbeforedemagSupplementaryv51.docx Supplementary Information: Femtosecond signatures of optically induced magnons before ultrafast demagnetization Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7456026","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":513504823,"identity":"a950219a-9600-4dae-b9b6-ac8c5af12253","order_by":0,"name":"Reza Rouzegar","email":"","orcid":"","institution":"Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany","correspondingAuthor":false,"prefix":"","firstName":"Reza","middleName":"","lastName":"Rouzegar","suffix":""},{"id":513504824,"identity":"827aa110-3cce-4d41-846a-a48d9c85f90b","order_by":1,"name":"Oliver 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On the 100 fs time scale, the magnetization dynamics is widely understood in the context of temperature models considering energy transfers between conduction electrons, magnons and crystal lattice. However, on even faster time scales, the flow of both angular momentum and energy between these subsystems has so far not been studied. Here, we measure ultrafast demagnetization by ultrabroadband THz-emission spectroscopy. We find that the rate of change of the magnetization does not rise instantaneously, but on a time scale shorter than 10 fs. In the framework of a general model of the three interacting subsystems, this rise is a signature that a transfer of angular momentum from magnons to conduction electrons proceeds in less than 10 fs, before substantial demagnetization has happened. We further conclude that most of the spin dissipated by the crystal lattice is transferred via magnon-lattice rather than electron-lattice interaction. 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