Ultrafast magnetization dynamics is an important issue for both fundamental science and for applications in order to optimize spin manipulation on a microscopic level. In order to progress in the understanding of such microscopic ultrafast mechanisms, it is now possible to probe absolute values of magnetization with a high temporal resolution (100 fs). In this context, we have used ultra-short optical laser pulses (60 fs duration) to induce changes of the magnetization in ferromagnetic films (Time resolved XMCD Spectroscopy and X-PEEM – Temperature effects). More recently, ultra-short and intense X-ray pulses have also been used as a pump in the context of ultra-fast magnetization dynamics (X-FEL).
XMCD uses the difference in the absorption cross sections between circular right and left polarized light when the X-ray energies are tuned to specific core levels in solids. The absorption signal can be used to trigger spin and orbital magnetic moments in ferromagnetic systems.
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 magnetization dynamics and electronic structure dynamics as a function of the delay with a fs laser excitation. The slicing set up is represented in the fifure below.
In our recent experiment we could evidence the two components of the magnetic moments (L and S) and (...)
Photon flux at present fs-slicing X-ray sources is just large enough to observe a change in spectroscopic contrast preventing more detailed in the femto second time scale, especially spatially resolved insight into the demagnetization process itself. Due to the significantly higher femtosecond X-ray intensity of X-FEL’s (LCLS Stanford – FLASH- Hamburg), this limitation can now be overcome. Actual goal is snapshot imaging of the temporal evolution of the magnetic domain structure upon the (...)
A more “standard” imaging technique uses secondary electrons emitted under the excitation of polarized X-rays (X-PEEM). This technique has been recently associated to a pump probe set up using a femto second laser as a pump und synchronized X-rays as a probe. 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. Recently, our group has studied two related aspects in the field of (...)