1. Magnetization dynamics

2. Only x-rays combine sub-ns time resolution with sub 100nm spatial resolution!

3. Magnetism: The reservoirs
The fundamental interactions
The micromagnetic picture
fs to ps dynamics
Very complex
Time scale: 100ps to years

4. The two dynamic regimes
Ultrafast demagnetization
Precession and damping
E. Beaurepaire, et al., Phys. Rev. Lett. 76, 4250 (1996)

5. Time resolved MOKE

6. The sample

7. Direct observation of the precession
Y. Acremann et al., Science 290, p492 (2000)

8. Magnetic eigenmodes

10. Time Resolved Photo Emission Electron Microscope
Pump laser beam
Electron optics
Auston switch
Synchrotron radiation

11. Response to the magnetic field pulse
(~300 ps in the beginning )
Observation x-rays

12. Hidden Parameter in the Domain Structure
Choe et al., Science 304, 420 (2004).

13. Vortex at the domain wall crossing

14. Response to a fast field pulseH
slow
fast (<1ns)
The response to a fast pulse is determined by the precession of the magnetization, not by relaxation!

15. Vortex moves parallel or antiparallel to the applied field direction
As the vortex drags the domain wall, it determines
the dynamics of the whole domain structure!.

16. Scanning transmission x-ray microscopy (STXM)
Spatial resolution: 30nm
Temporal resolution: 70ps
Elemental selectivity
Magnetic contrast

17. Imaging magnetism with x-rays: X-ray Magnetic Circular Dichroism (XMCD)
Transition Metal (e.g. Fe, Co, Ni)
Core  Valence excitation of electrons
Polarization dependent absorption of x-rays
Depends on: number of holes, spin and orbital moment

18. Switching of the vortex core
Van Waeyenberge et al., Nature 444, 461 (2006).