Proceedings Article | 10 September 2019
KEYWORDS: Terahertz radiation, Interfaces, Metals, Gold, Spintronics, Ferromagnetics, Fermium, Frequency modulation, Picosecond phenomena, Spectroscopy
Spin-Hall Effects and spin-charge conversion phenomena at a short lengthscale either using heavy metals like Pt, W [1], Au:W [2] , Inverse-Edelstein Effect at Rashba [3] or topological interface [4] are the basis of new spintronics functionalities. Combined with FMR spin- pumping, spin-orbit interactions in these systems and heterostructures also enable to probe the interfacial properties possibly involving spin-orbit coupling effects like local spin-loss (SML) at 3d/5d interfaces [5-6]. Beyond, it was recently reported that THz emission may be realized via dynamical spin-to charge conversion in the picosecond scale in the same kind of heterostructures, either metallic [7] or Rashba system [8-9], composed of ferromagnetic (FM) and spin-orbital active materials using time- dependent spectroscopy (TDS) techniques. Here, experiments consist in exciting magnetization and spin-currents within the FM layer via femtosecond laser excitation and measuring, in the picosecond timescale, the relaxation of the correlated spin and charge currents responsible for THz dipolar emission. The spintronics THz emitters typically reaches the power of ZnTe electro-optic semiconductor technology or even higher. In that mind, we will present our last results of THz emission provided by optimized growth bilayers composed of a high-spin orbit material in contact with a ferromagnetic layer like Co/Pt, Co/Ti/Pt, Co/Au/Pt, NiFe/Au:W, Co/Pt/Au:W) including Ti or Au monolayers (MLs) insertion and Au:W spin-sink materials. Those state-of-the art bilayers are analyzed using complementary experiments combining RF-spin-pumping-ISHE measurements and TDS –THZ spectroscopy. Our results show, that in some conditions, the insertion of Ti or AuW based materials in Co/Pt structures may enhance either THz or ISHE signals depending on the layer sequence. In particular, the ML insertion in Co/Ti(ML)/Pt systems evidences a decrease of the spin-orbit strength at the interface, responsible for an increase of the ISHE signal by decrease of SML, conjugated to a decrease of FMR-linewidth and THz emission. We will demonstrate the strict correlation between THz signals and related spin-mixing conductances as well as ISHE signals and will discuss the connection between THz and spin loss phenomena. In particular, the THz signal can be viewed as a straightforward and non-destructive method to probe the Rashba spin-orbit strength and spin-orbit coupling of Interface Shockley states between transitions metals
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