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MA: Fachverband Magnetismus

MA 37: Spin Dependent Transport Phenomena

MA 37.14: Vortrag

Donnerstag, 26. März 2009, 18:45–19:00, HSZ 403

Femtosecond spin dynamics induced by ballistic transport of spin-polarized carriers in Au/Fe/MgO(001) — A. Melnikov¹, I. Razdolski², T. Wehling³, A. Lichtenstein³, E. Papaioannou¹, Ch. Rüdt¹, P. Fumagalli¹, O. A. Aktsipetrov², and •U. Bovensiepen¹ — ¹Freie Universität Berlin, Fachbereich Physik, 14195 Berlin, Germany — ²Physics Department, Moscow State University, Moscow, 119992, Russia — ³Institut für Theoretische Physik, Universität Hamburg, 20355 Hamburg, Germany

Scattering of hot carriers can be studied by ballistic electron microscopy. Here, we present a complementary approach using femtosecond laser pulses in a pump-probe experiment. We demonstrate an all-optical back-pump front-probe scheme to analyze the transport of spin-polarized hot carriers through Au/Fe/MgO(001). We excite hot carriers in 15 nm thick Fe by absorption of an 800 nm laser pulse. The spin-polarized hot carriers propagate subsequently at the Fermi velocity through the layer stack. A time-delayed second laser pulse generates its optical second harmonic (SH) in reflection at the opposite Au surface. We monitor the SH intensity as a function of pump-probe delay for opposite Fe magnetization directions, which facilitates an analysis of the spin and carrier propagation through Au. From the observed transfer time and its broadening we conclude that the carriers propagate ballistically for 50 nm Au and diffusively for 100 nm. Interestingly, the magneto-optical signal changes its sign after 500 fs, which is discussed in terms of local spin reorientation and different propagation velocities for minority and majority carriers.