Team members : Boeglin C., Bergeard N., Pacé M., Gupta D.
The group research focus is the investigation of magnetic nanomaterials and their ultrafast dynamics (ps – fs) using X-ray imaging and X-ray spectroscopies. The experiments are performed at Synchrotron SOLEIL, BESSY, SLS and at Free Electron Lasers (FEL), Stanford-LCLS and Hamburg-FLASH
The two axis of research:
Quantitative spectroscopies and ultrafast magnetization dynamics:
The capability of X-rays to differentiate between changes in the electronic and the spin structure has led to new insight into the demagnetization processes. Using the slicing facilities at HZB-BESSY we are able to study the dynamics of spin and orbital moments and the dynamics of the electronic structure as a function of the delay between the femtosecond laser excitation and the X-ray probe pulse.
Imaging ultrafast dynamics of the magnetic domains.
Photon flux at the present femtoslicing source is just large enough to observe a change in spectroscopic contrast preventing more detailed in the femtosecond time scale, especially spatially resolved insight into the demagnetization process itself. Due to the significantly higher femtosecond X-ray intensity of X-FEL’s, this limitation can now be overcome. This technique allows snapshot imaging with sub 100 nm spatial resolution using single x-ray pulses. The X-PEEM imaging technique uses secondary electrons emitted under the excitation of polarized X rays. The actual limited time resolution of 50 ps of this imaging technique is compensated by real space imaging of magnetic domains with spatial a resolution of 30 nm.
Recent research and publications:
Ultrafast Magnetization Dynamics
Ultrafast lasers produce short pulses ( <100 fs), but a spatial resolution that is generally limited by the wavelength of the probe light. X rays, on the other hand, allow for high spatial resolution and high contrast imaging at the elemental absorption edges of ferromagnetic materials but suffers from lower time resolution. Recently femtosecond laser pulses are used to slice short burst of X rays (~100 fs) from synchrotron radiation. We use such short pulses of X rays in order to study the ultrafast dynamics of specific magnetic elements (Fe, Co, Gd, Tb,…) and possible transfer of angular momenta between them.
Ultrafast Dynamics of L(t) and S(t)
– N. Bergeard, V. López-Flores, V. Halté, C. Stamm, N. Pontius, M. Hehn, E. Beaurepaire, and C. Boeglin et al. « Ultrafast angular momentum transfer in multisublattice ferrimagnets.” Nature Communications 5, 3466 (2014).
– V. López-Flores, N. Bergeard, V. Halté, C. Stamm, N. Pontius, M. Hehn, E. Otero, E. Beaurepaire, and C. Boeglin « Role of critical spin fluctuations in ultrafast demagnetization of transition-metal rare-earth alloys.” Phys. Rev. B 87, 214412 (2013)
– V. López-Flores, V. Halté, , J. Arabski, C. Stamm, V. Halté, N. Pontius, E. Beaurepaire, C. Boeglin « Ultrafast angular momentum transfer studied by time-resolved X-ray magnetic circular dichroism.” Phys. Rev. B 86, 014424 (2012)
– C. Boeglin, E. Beaurepaire, V. Halté, V. López-Flores,C. Stamm, N. Pontius, H.A. Durr and J-Y Bigot « Distinguishing the ultrafast dynamics of spin and orbital moments in solides » Nature 465, p458 (2010)
Ultrafast Dynamics at the Nanoscale
– T. Wang,, D. Zhu, B. Wu, C. Graves, S. Schaffert, T. Rander, L. Muller, B. Vodungbo, C. Baumier, D. P. Bernstein, B. Bräuer, V. Cros, S. de Jong, R. Delaunay, A. Fognini, R. Kukreja, S. Lee, V. Lopez-Flores, J. Mohanty, B. Pfau, H. Popescu, M. Sacchi, A. B. Sardinha, F. Sirotti, P. Zeitoun, M. Messerschmidt, Joshua J. Turner, W. F. Schlotter, O. Hellwig, R. Mattana, N. Jaouen, F. Fortuna, Y. Acremann, C. Gutt, H. A. Dürr, E. Beaurepaire, C. Boeglin, S. Eisebitt, G. Grübel, J. Lüning, J. Stöhr and A. Scherz “Femtosecond Single-shot X-ray Imaging of Nanoscale Ferromagnetic Order“, PRL108 , 267403 (2012)
– B. Vodungbo, J. Gautier, G. Lambert, A. Barszczak Sardinha, M. Lozano, S. Sebban, M. Ducousso, W. Boutu, K. Li, B. Tudu, M. Tortarolo, R.Hawaldar, R. Delaunay, V. Lopez-Flores, J. Arabski, C. Boeglin, H. Merdji, P. Zeitoun, and J. Luning, Nature Com. 3, 999 (2012), DOI : 10.1038/ncomms2007
– B. Vodungbo, A. Barszczak Sardinha, J. Gautier, G. Lambert, M. Lozano, S. Sebban, E. Meltchakov, F. Delmotte, V. Lopez-Flores, J. Arabski, C. Boeglin, E. Beaurepaire, R. Delaunay, J. Lüning and P. Zeitoun, “Table-top resonant magnetic scattering with extreme ultraviolet light from high-order harmonic generation”, Europhysics Letters, 94, 54003 (2011).