PGI-1 Seminar: Prof. Dr. Markus Münzenberg
Spin excitation and transport: our insight on fm time scales
- 22.Aug.2012 11:00
University of Göttingen
In my talk, I will touch areas of our work with hot spin physics. Femtosecond laser time resolved spectroscopy allows to study ultrafast heating and non-equilibrium processes: we can modify the spin relaxation channels via the material’s electronic structure, THz emission and high energy spin-wave relaxation paths can be designed [1,2]. Ultrafast excitation processes can be understood in two pictures: localized magnetism and itinerant spin-transport. In the first spin-flips processes are connected to local spin excitation that decays into high energy spin-waves. This stochastic spin-wave ensemble allows describing the dynamics and its characteristic time scales in atomistic calculations, coarse grained spin-wave models or the Landau-Lifshitz-Bloch equations . In the second, the excitation gradient results in charge and spin currents across layers and interfaces. In detail I will address novel effects of heat gradients on the nanoscale. In magnetic tunnel junctions, the Seebeck voltage can be controlled via the magnetization – the magneto-Seebeck effect . Changing from the parallel to the antiparallel orientation allows switching the thermopower in size and even in sign. This new effect originates from the tunnel junctions’ specific electronic structure, its half metallic like behavior of the tunnel junction transmission. Via non-thermalized gradients of electron exciation in ferromagnets we can even extend transport of spin-polarized electron bunches through a solid, preferably at frequencies reaching the so far unexplored terahertz (THz) regime. By experiment and theory it is demonstrated that the transport of femtosecond spin-current bursts can be controlled by using magnetic heterostructures and detected via their THz signal. The works presented are results from collaborations with O. Chubykalo-Fesenko,CSIC, Spain, A Thomas, Bielefeld University, M. Battiato, Uppsala University, Sweden T. Kampfrath, FHI Berlin, Germany.
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