Ultrafast laser-excited spin transport in Au/Fe/MgO(001): Relevance of the Fe layer thickness

Propagation dynamics of spin-dependent optical excitations is investigated by back-pump front-probe experiments in Au/Fe/MgO(001). We observe a decrease for all pump-probe signals detected at the Au surface, if the Fe thickness in increased. Relaxation processes within Fe limit the emission region of ballistic spins at the Fe/Au interface to ~1 nm. Recently, we have established magneto-optical femtosecond back-pump frontprobe experiments [1 ] in order to provide insight into spin-dependent (i) transport contributions in ultrafast magnetization dynamics and (ii) non-equilibrium transport in metallic films in general. Fig. 1. Scheme of back-pump front-probe experiment. The fs pump pulse at 800 nm is absorbed in the metallic bilayer after transmission through MgO(001) depending on the investigated Fe layer thickness dFe, here 2, 11, and 17 nm. The dynamics of excitations propagating through the bilayer stack to the Au surface is probed by magneto-induced second harmonic generation (mSHG) as a function of time delay between pump and probe pulses.