Magnetic Switching in Granular FePt Layers Promoted by Near-Field Laser Enhancement

Patrick W. Granitzka, Emmanuelle Jal, Loïc Le Guyader, Matteo Savoini, Daniel J. Higley, Tianmin Liu, Zhao Chen, Tyler Chase, Hendrik Ohldag, Georgi L. Dakovski, William F. Schlotter, Sebastian Carron, Matthias C. Hoffman, Alexander X. Gray, Padraic Shafer, Elke Arenholz, Olav Hellwig, Virat Mehta, Yukiko K. Takahashi, Jian WangEric E. Fullerton, Joachim Stöhr, Alexander H. Reid, Hermann A. Dürr

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between "up" and "down" magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. The fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.

Original languageEnglish
Pages (from-to)2426-2432
Number of pages7
JournalNano Letters
Issue number4
Publication statusPublished - 2017 Apr 12


  • FePt
  • X-ray scattering
  • magnetic switching
  • pump-probe
  • ultrafast magnetism


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