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18/04/2023 -Séminaire exceptionnel - Anne Bernand-Mantel

Mardi 18 avril 2023 à 14h00, Anne Bernand-Mantel (Université de Toulouse) donnera un séminaire dans l’Auditorium de TRT.
Titre  : Skyrmion theory in magnetic thin films : the role of non-local magnetic dipolar interaction
Résumé  : Compact magnetic skyrmion are potential bit-encoding states for spintronic memory and logic applications that have been the subject of a rapidly growing number of studies in recent years. Nevertheless, despite numerous attempts, a satisfactory theoretical description of these objects is still lacking today due to the highly non-trivial character of the magnetostatic interaction that plays a major role in determining the nature of magnetization patterns in ferromagnetic materials. The orthodox theory of skyrmions in ultrathin ferromagnetic layers with interfacial DMI relies on a model that accounts for the dipolar interaction through an effective anisotropy term, neglecting long-range effects. At the same time, in single ferromagnetic layers with interfacial DMI, large chiral skyrmions, also called skyrmionic bubbles have been observed, suggesting a non-trivial interplay between DMI and long-range dipolar effects [1]. We will present our recent work where we used rigorous mathematical analysis to develop a skyrmion theory that takes into account the full dipolar energy in the thin film regime and provides analytical formulas for compact skyrmion radius, rotation angle and energy [2,3]. Our theory reveals the existence of a new regime at low DMI were skyrmions are stabilized by a combination of non-local dipolar interaction and a magnetic field applied parallel to their core [2-4]. This predictions are confirmed by our numerical simulations. We will also present our recent theory of skyrmion lifetime based on the continuum field theory where we exploit the fundamental properties of the exchange energy and interpret skyrmion collapse events as capture by an absorber at microscale. This yields to an explicit Arrhenius collapse rate for skyrmions with both the barrier height and the prefactor as functions of all the material parameters [5]. Or work provides a guide in material system design in view of optimizing the skyrmion lifetime for applications.
[1] A. Bernand-Mantel et al. Scipost 4, 27 (2018)
[2] A. Bernand-Mantel, Cyrill Muratov, Thilo Simon, Physical Rev. B101, 045416 (2020)
[3] A. Bernand-Mantel, Cyrill Muratov, Theresa Simon, Archive for Rational Mechanics and
Analysis 239 219 (2021)
[4] A. Bernand-Mantel, A. Fondet, S. Barnova, T. M. Simon and Cyrill B. Muratov (in
[5] A. Bernand-Mantel, Cyrill Muratov, Valery Slastikov PNAS 119 e2122237119 (2022)


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