THz Emission from metallic bilayers

It was recently reported that THz emission can be realized in heterostructures composed of ferromagneticand non-magnetic metal thin films via dynamical spin-to charge conversion. This occursfrom interfacial Rashba spin-orbit coupling or inverted spin-Hall effect (ISHE) and evidencedvia time-dependent spectroscopy. This particular work and objectives focus on last results ofTHz emission provided by optimized growth bilayers composed of a high-spin orbit material anda ferromagnetic layer Co/Pt in different configurations by inserting gold, titanium and rutheniumthin layers for better electronic matching. Those bilayers state-of-the-art analysis is based on experimentscombining RF-spin pumping and spin-to-charge conversion by ISHE . The THzexperiments consist in exciting magnetization and spin-currents within the FM layer via femtosecondlaser excitation and measuring, in the picosecond timescale, the relaxation of the correlatedspin and charge currents responsible for THz dipolar emission. The advantages of the THz emitterbased on magnetic heterostructures are low-cost and the polarization of emitted THz wave beingeasily tuned with an external magnetic field. Particular interesting are the results for the configurationCo/Pt/Au:W for which the THz signal is higher with respect to Co/Pt, even if the ISHE signalis still larger for the latter. To understand this point, it will be important to discuss the role of thegeneralized spin-mixing conductance. THz signals strongly depend on the spin Hall angle of non-FM metal, spin diffusion length, and spin-mixing conductance. Since in this work spin hall angleand spin diffusion length are considered as constants, mainly because the non-magnetic materialis always the same (Pt), it should be possible to find that in the structures with large spin-mixingconductance or larger spin transmission the THz signal becomes higher. My internship work andpresent report mainly demonstrate that FMR-ISHE experiment becomes a relative fast and reliablemethod to study THz emission for these spintronic samples and to predict possible optimizations.