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Ultrafast Spin Dynamics and Spin Manipulation

Date Do, 07.04.2011 - Do, 07.04.2011
Time 10.15
Speaker Prof. Dr. Mathias Kläui, Laboratory of Nanomagnetism and Spin Dynamics, SwissFEL, Paul Scherrer Institut & Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne
Location Universität Bern, Institut für Angewandte Physik, Gebäude exakte Wissenschaften, Hörsaal B116, Sidlerstrasse 5, 3012 Bern
Program So far conventional magnetic fields have been used to excite spin dynamics and manipulate magnetization. While this approach is now reasonably well understood and widely employed in devices, it entails limitations for the speed of magnetic switching as intrinsically the spin dynamics is limited by the precession frequency corresponding to the magnetic field.
To overcome this limitation and explore the rich physics of the interaction between spin currents, photons and the magnetization, we have used spin-polarized charger carriers and photons to excite spin dynamics and manipulate the magnetization on ultrafast timescales.
Spin-polarized currents can directly transfer spin angular momentum to the magnetization, leading to fast switching of multilayer nanopillars (reciprocal effect to the Giant Magnetoresistance effect for which the Nobel prize was awarded 2007) and the generation of GHz microwave oscillations. We have shown how the dynamics of inhomogeneous spin textures, such as domain walls can be efficiently controlled using such large spin transfer torques [1] and we have explained how pure diffusive spin currents can induce even more efficient switching [2].
Using photons allows us to overcome the time limitations imposed by the charge carrier drift and diffusion dynamics and to studyon the femtosecond timescale the fundamental ultrafast energy and angular momentum transfer between the electron, spin and lattice systems. We have used optical laser pulses to study the angular momentum pathways leading to ultra-fast demagnetization in advanced materials [3]. Recent measurements at Free Electron Laser sources (where potentially sub-femtosecond time resolution can be achieved) reveal the dependence on the nanoscale spin structure.
[1] M. Eltschka et al., Phys. Rev. Lett. *105*, 56601 (2010); L. Heyne et al., Phys. Rev. Lett. *105*, 187203 (2010) - see Viewpoint article: Physics *3*, 91 (2010). [2] D. Ilgaz et al., Phys. Rev. Lett. *105*, 76601 (2010). [3] J. Walowski et al., Phys. Rev. Lett. *101*, 237401 (2008)
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