Ultrafast demagnetization dynamics
When an ultrashort optical laser pulse excites a magnetic material, it responds with an almost instantaneous reduction of its magnetization, followed by a slower recovery. This dynamics can be followed by time resolved magnetic holography, taking FEL images of samples excited by IR pulses.
von Korff Schmising et al., Physical Review Letters 112, 217203 (2014).
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The Co/Pd magnetic specimen is covered by a gold holographic mask with 50 nm reference holes and a 2.4 μm long ellipsoidal sample area, that concentrates most of the IR pump intensity on a limited spot. Magnetic holograms are acquired integrating over several FEL pulses, tuned at the Co M-edge to enhance the sample magnetic photon scattering, impinging at a known delay after each IR pump. At each delay, an image of the domain structure is obtained applying a single Fourier transform of the holographic diffraction pattern. Magnetic contribution is enhanced taking the difference of images acquired with right and left circularly polarized FEL light. |
Thanks to the intensity and spectral stability of FERMI@Elettra, the experiment can be carried out in integration mode, with fast demagnetization probed after each pump pulse and total recovery before the next pump, without modification of the domain configuration or sample damage. Retrieve articleImaging Ultrafast Demagnetization Dynamics after a Spatially Localized Optical Excitation.
C. von Korff Schmising, B. Pfau, M. Schneider, C.M. Günther, M. Giovannella, J. Perron, B. Vodungbo, L. Müller, F. Capotondi, E. Pedersoli, N. Mahne, J. Lüning, S. Eisebitt. |
