【10/23】IMR / AIMRジョイントセミナー
IMR / AIMR Joint Seminar on Spintronicsのご案内
Femtosecond Spin Transfer
Prof. Dr. Bert Koopmans
(Eindhoven University of Technology, The Netherlands)
Novel schemes for controlling the ferromagnetic state at the femtosecond time scale by pulsed laser excitation have received great current interest recently. Driving systems into the strong non-equilibrium regime, it has been shown possible not only to quench magnetic order by femtoseond laser pulses, but also to drive systems from the anti- to ferromagnetic state, switch by circularly polarized light, and toggle-switch the ferrimagnetic state exploiting internal exchange interactions. More recently, it has been proposed that laser-induced super-diffusive spin currents over several to tens of nanometers can also be an important source of sub-picosecond magnetization dynamics. At present, the relative importance of local dissipation of angular momentum versus transfer of spin angular momentum between different regions in the laser excited material is hotly debated.
In this seminar I will start by reviewing recent developments, and discuss the local dissipation of angular momentum via Elliott-Yafet spin-flip scattering as a feasible scenario for many of the recently observed phenomena. Then I will present a number of recent experiments on especially engineered multilayer systems that unambiguously demonstrate that –besides local dissipation– laser-induced inter-layer spin transfer does take place, and can significantly modify the magnetization dynamics. Even more excitingly, it turns out possible to apply a true laser-induced spin transfer torque on a free magnetic layer, using a collinear multilayer configuration consisting of a free in-plane layer on top of a PMA injection layer and separated by a nonmagnetic spacer. This approach could be of relevance for future all-optical switching technologies, but also provides highly relevant quantitative input to the debate as to the relative importance of spin transfer to laser-induced demagnetization.