Peter Grünberg Institut (PGI)

Elektronische Eigenschaften (PGI-6)

Magnetization Dynamics Group

Spin manipulation in ferromagnetic thin films by optical excitation is one the most fascinating topics of the current solid state research. Optical spin control can provide a key technology for future advanced ultrafast low energy consumption electronics. Nevertheless, the underlying physical mechanism of the process is still under debate. Further insights require new experimental tools and theoretical approaches that allow detailed analysis of the observed phenomena. In our laboratory, we explore non-equilibrium spin dynamics in ferromagnetic thin films and multilayers with time resolution below 30 femtoseconds and featuring elemental selectivity. This unique combination has been reached world-wide only recently by a fast progress in the generation of laser high-order harmonics that can reach the extreme ultraviolet (XUV) spectral range. Tuning the XUV light to resonance with 3d electron shallow core levels of the examined material then allows a resonant enhancement of the signal for the particular element.

By using laser fundamental light in near infrared (1.5eV) as optical pump and XUV (up to 72 eV) as probe we can gain unique insight into the physics governing spin dynamics in complex ferromagnetic materials, alloys and multilayers (see project description in Section1 for more details).

An additional pump-probe experiment operated purely in the visible spectral range (for details see Section2) is well-suited to provide complementary information to our IR- pump XUV-probe experiments and study the in-plane as well as the out-of-plane magnetization of thin magnetic films. This setup is currently also used in all-optical switching experiments (Section 4).

The short wavelength XUV light (l~20 nm)allows not only access to elemental selectivity but is also used to provide insight into magnetic domain dynamics and its structure on nanometer length scales in resonant magnetic scattering experiments (Section 3).

The idea of an optical control and a permanent change of the magnetization state in ferromagnetic superlattices induced by femtosecond laser pulses has been mainly driven by the potential of its use in ultrafast magneto-optic storage. We investigate the range of material- and laser parameters that play a role in the switching process in ferromagnetic (Co/Pt)n multilayers – a completely new set of switchable magnets discovered only recently (for details see Section 4)

To reach even higher photon energies and flux in the XUV spectral range is the main goal of the ‘metallic target’ project.

Here, metallic microspheres are illuminated with high power laser to yield bright bursts of high energy photons. This novel XUV source could be in future a valuable tool in experimental solid-state physics (see details in Section 5).

The main scientific activities of the laser group are outlined below.