Ultrafast laser techniques have revealed extraordinary spin dynamics in magnetic materials1,2,3,4,5,6 that equilibrium descriptions of magnetism7 cannot explain. Particularly important for future applications is understanding non-equilibrium spin dynamics following laser excitation on the nanoscale, yet the limited spatial resolution of optical laser techniques has impeded such nanoscale studies. Here we present ultrafast diffraction experiments with an X-ray laser that probes the nanoscale spin dynamics following optical laser excitation in the ferrimagnetic alloy GdFeCo, which exhibits macroscopic all-optical switching4,8,9. Our study reveals that GdFeCo displays nanoscale chemical and magnetic inhomogeneities that affect the spin dynamics. In particular, we observe Gd spin reversal in Gd-rich nanoregions within the first picosecond driven by the non-local transfer of angular momentum from larger adjacent Fe-rich nanoregions. These results suggest that a magnetic material’s microstructure can be engineered to control transient laser-excited spins, potentially allowing faster (~ 1 ps) spin reversal than in present technologies10,11,12.
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Research at Stanford is supported by US DOE, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract DE-AC02-76SF00515. Portions of this research were carried out on the SXR Instrument at the Linac Coherent Light Source (LCLS), a division of SLAC National Accelerator Laboratory and an Office of Science user facility operated by Stanford University for the US Department of Energy. The SXR Instrument is funded by a consortium whose membership includes the LCLS, Stanford University through the Stanford Institute for Materials Energy Sciences (SIMES), Lawrence Berkeley National Laboratory (LBNL), University of Hamburg through the BMBF priority program FSP 301, and the Center for Free Electron Laser Science (CFEL). In addition, other portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the US Department of Energy Office of Science by Stanford University. C.E.G. is a NSF Graduate Research Fellow. This work was also supported by the European Community’s Seventh Framework Programme FP7/2007-2013 (grants NMP3-SL-2008-214469 (UltraMagnetron) and 214810 (FANTOMAS)), the European Research Council ERC Grant agreement No. 257280 (Femtomagnetism), the Foundation for Fundamental Research on Matter (FOM), the Netherlands Organization for Scientific Research (NWO), the Nihon University Strategic Projects for Academic Research, the DFG grant SFB925, the Excellence cluster ‘Frontiers in Quantum Photon Science’ and the Max Planck Society through development and operation of the pn-CCD cameras at CFEL. We are grateful to A. Marshall for assistance and discussion on STEM–EDX measurements.
The authors declare no competing financial interests.
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Graves, C., Reid, A., Wang, T. et al. Nanoscale spin reversal by non-local angular momentum transfer following ultrafast laser excitation in ferrimagnetic GdFeCo. Nature Mater 12, 293–298 (2013). https://doi.org/10.1038/nmat3597
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