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Being able to manipulate magnetic structures in non-trivial ways such as by the application of a magnetic field, is interesting from fundamental point of view as well as from that of applications. Manipulating them on ultrafast time scales is even more exciting and challenging. Here I like to address the ultrafast magnetization dynamics of antiferromagnets, for which a microscopic understanding of the spin dynamics can be obtained by x-ray (resonant) diffraction using ultra-short x-ray pulses, today obtainable on X-ray-Free-Electron-Laser (XFEL) sources, such as the LCLS and SACLA. I will give examples on ultra-fast demagnetization on simple elemental Ho [1], on CuO, [2,3] which are in strong contrast to the results obtained on TbMnO₃. [4] At the end I hope I will show you the potential to obtain ultrafast all optical switching in oxides by switching the magnetic structure and the ferroelectric polarization in a multiferroic. [5]

[1] L. Rettig et al., submitted
[2] S. L. Johnson et al., Phys. Rev. Lett. 108, 037203 (2012).
[3] U. Staub et al., Phys. Rev. B 89, 220401(R) (2014).
[4] J. Johnson et al., Phys. Rev. B in press (arXiv:1507.06628)
[5] T. Kubaka et al., Science 343,1333 (2014).

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