Ultrafast spin currents and charge conversion at interfaces probed by THz and GHz spectroscopy

Recent developments in nanomagnetism and spintronics allowed the usage of ultrafast spin physicsforTHz emission. The so-called field of THz spintronics is a novel direction that combines magnetism with optical physics and ultrafast photonics. The physical mechanism of the THz emission is based on the inverse spin Hall effect and the experimental scheme of the field involves the use of femtosecond laserpulses to trigger ultrafast spin and charge dynamics. The technological and scientific key-challenges to controland increase the emission from THz spintronic emitters requires the understanding and the control of the source of the radiation, namely the transport of the ultrafast spin-and charge current. In this presentation, I will address the spin-to-charge conversion phenomena at ferromagnetic (FM)-non-magnetic (NM) transition metal interfaces that lead to the THz emission. The focus will be on the interface engineering for the optimization of the spin transmission. The spin transmission efficiency at interfaces will be addressed by combining quasi-static excitation regime using ferromagnetic resonance-spin pumping technique with time-domain terahertz spectroscopy. Based on our latest results I will demonstrate the ability to control the emitted THz radiation by modifying the defect density in the layers and the FM/NM interface transmission for spin-polarized electrons. The presented results will define a road map of efficient THz emission in terms of materials, geometrical stack, and interface quality that is essential for future applications of metallic spintronic THz.