Abstract
Spintronic structures are extensively investigated for their spin–orbit torque properties, required for magnetic commutation functionalities. Current progress in these materials is dependent on the interface engineering for the optimization of spin transmission. Here, we advance the analysis of ultrafast spin-charge conversion phenomena at ferromagnetic-transition metal interfaces due to their inverse spin-Hall effect properties. In particular, the intrinsic inverse spin-Hall effect of Pt-based systems and extrinsic inverse spin-Hall effect of Au:W and Au:Ta in NiFe/Au:(W,Ta) bilayers are investigated. The spin-charge conversion is probed by complementary techniques—ultrafast THz time-domain spectroscopy in the dynamic regime for THz pulse emission and ferromagnetic resonance spin-pumping measurements in the GHz regime in the steady state—to determine the role played by the material properties, resistivities, spin transmission at metallic interfaces, and spin-flip rates. These measurements show the correspondence between the THz time-domain spectroscopy and ferromagnetic spin-pumping for the different set of samples in term of the spin mixing conductance. The latter quantity is a critical parameter, determining the strength of the THz emission from spintronic interfaces. This is further supported by ab initio calculations, simulations, and analysis of the spin-diffusion and spin-relaxation of carriers within the multilayers in the time domain, permitting one to determine the main trends and the role of spin transmission at interfaces. This work illustrates that time-domain spectroscopy for spin-based THz emission is a powerful technique to probe spin-dynamics at active spintronic interfaces and to extract key material properties for spin-charge conversion.
Highlights
The terahertz (THz) frequency range of the electromagnetic spectrum is generally defined as extending from 0.3 to 10 THz
A widespread method is based on THz time-domain spectroscopy (TDS) where THz pulses are typically generated from nonlinear optical crystals via optical rectification or from photoconductive switches with ultrafast transient currents when excited by an ultrashort near-infrared femtosecond oscillator.[3]
A is related to the laser pump power, Dt is the laser pulse duration, and sr is the initial proportion of the spinchannel excited owing to the different density of states nd;r of the d-band
Summary
H.; Hawecker, J.; Rongione, E.; Baez Flores, G.; To, D. C.; Nong, H.; Mangeney, J.; Tignon, J.; Godel, F.; Collin, S.; Seneor, P.; Bibes, M.; Fert, A.; Anane, M.; George, J. M.; Vila, L.; CossetCheneau, M.; Dolfi, D.; Lebrun, R.; Bortolotti, P.; Belashchenko, Kirill; Dhillon, S.; and Jaffrès, H., "Ultrafast spin-currents and charge conversion at 3d-5d interfaces probed by time-domain terahertz spectroscopy" (2020). This Article is brought to you for free and open access by the Research Papers in Physics and Astronomy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Kirill Belashchenko Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.
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