Photon Energy-Dependent Ultrafast Magnetization Dynamics in Magnetic Heterostructures

Photon Energy-Dependent Ultrafast Magnetization Dynamics in Magnetic Heterostructures | 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 Article Photon Energy-Dependent Ultrafast Magnetization Dynamics in Magnetic Heterostructures Fabian Rotermund, In Cheol Yu, San Ko, Wontae Kim, Byong-Guk Park, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6249947/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Dec, 2025 Read the published version in Communications Materials → Version 1 posted You are reading this latest preprint version Abstract Laser-induced ultrafast demagnetization has traditionally been understood as a process in which photon absorption excites nonequilibrium electrons, leading to demagnetization followed by magnetization recovery. It has been widely assumed that the time scale of these dynamics is governed primarily by the total absorbed laser power rather than the specific photon energy. In this study, we present evidence that challenges this assumption. By employing spintronic terahertz emission spectroscopy in magnetic heterostructures, we reveal that the time scales of both demagnetization and recovery systematically vary with laser wavelength, i.e., photon energy. Specifically, magnetization dynamics induced by shorter-wavelength optical pulses evolve over significantly longer time scales than those triggered by longer-wavelength infrared pulses, even when the total absorbed laser power remains constant. Our findings suggest that higher-energy (shorter-wavelength) photons enhance magnon excitation, which in turn drives spin transport across the magnet/nonmagnet interface, thereby modifying the magnetization dynamics. These results uncover a previously overlooked influence of laser photon energy on ultrafast magnetization dynamics, offering new opportunities for optical control of spintronic phenomena. Physical sciences/Optics and photonics/Optical physics/Magneto-optics Physical sciences/Optics and photonics/Optical physics/Terahertz optics Full Text Additional Declarations There is NO Competing Interest. Supplementary Files 20250317SIfinal.docx Supplementary information Cite Share Download PDF Status: Published Journal Publication published 09 Dec, 2025 Read the published version in Communications Materials → 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-6249947","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":434854221,"identity":"ac6533f4-f0dc-4fc4-a99f-731aae1c365a","order_by":0,"name":"Fabian Rotermund","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIie3OIQvCQBTA8TcOtjK03kDmV7ixoOCX2UOYRSwWbRvCbJr9FqZlx8FWzr5hUQSzNoUFp2JSTm2G+4fHg7sfPACV6q/LIgDvsZIPX5/vIr0R9gvJ/dv8grSm82Q/7vNBrTjgcVuWUJ+uiDuSkIbgxFnHfGhtfE4xYkCFR1BICKVd3QpjjstNL6AYVIflQJJATozLnRTZ5OyVDJpfEF27k1xPqaczYBVBKTG5Wx3Ww4Xw/TZGrukInDhSYoS7Uxh3cJalbnEubdvOOLdk5CUTQPsJqFQqlepNV2dXT02smcvMAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-9053-3916","institution":"Korea Advanced Institute of Science and Technology (KAIST)","correspondingAuthor":true,"prefix":"","firstName":"Fabian","middleName":"","lastName":"Rotermund","suffix":""},{"id":434854222,"identity":"1eb3d5d7-87eb-4ed7-84d9-49d453cea493","order_by":1,"name":"In Cheol Yu","email":"","orcid":"https://orcid.org/0000-0003-1788-1521","institution":"Korea Advanced Institute of Science and Technology (KAIST)","correspondingAuthor":false,"prefix":"","firstName":"In","middleName":"Cheol","lastName":"Yu","suffix":""},{"id":434854223,"identity":"0efc5094-b459-40ce-b8fb-e133d5faa708","order_by":2,"name":"San Ko","email":"","orcid":"","institution":"KAIST","correspondingAuthor":false,"prefix":"","firstName":"San","middleName":"","lastName":"Ko","suffix":""},{"id":434854224,"identity":"a1ba869a-9c3b-4c17-874b-ea2d5256637f","order_by":3,"name":"Wontae Kim","email":"","orcid":"","institution":"Samsung Electronics Co. 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