Spin Injection Efficiency at Metallic Interfaces Probed by THz Emission Spectroscopy

Abstract

Terahertz (THz) spin‐to‐charge conversion has become an increasingly important process for THz pulse generation and as a tool to probe ultrafast spin interactions at magnetic interfaces. However, its relation to traditional, steady state, ferromagnetic resonance techniques is poorly understood. Here, nanometric trilayers of Co/X/Pt (X = Ti, Au or an Au:W alloy) are investigated as a function of the “X” layer thickness, where THz emission generated by the inverse spin Hall effect is compared to the Gilbert damping of the ferromagnetic resonance. Through the insertion of the “X” layer it is shown that the ultrafast spin current injected in the non‐magnetic layer defines a direct‐spin‐conductance, whereas the Gilbert damping leads to an effective spin‐mixing‐conductance of the trilayer. Importantly, it is shown that these two parameters are connected to each other and that spin‐memory‐losses can be modeled via an effective Hamiltonian with Rashba fields. This work highlights that magneto‐circuit concepts can be successfully extended to ultrafast spintronic devices, as well as enhancing the understanding of spin‐to‐charge conversion processes through the complementarity between ultrafast THz spectroscopy and steady state techniques.

Ultrafast Spin‐Charge Conversion at SnBi2Te4/Co Topological Insulator Interfaces Probed by Terahertz Emission Spectroscopy

“…These experiments rely on ultrafast spin injection and their conversion into a charge current at TI material interfaces as explored recently for Bi/Bi 2 Te 3 systems. [22] THz emission TDS has proven to be a relevant experimental method [32][33][34] and is particularly important to probe the spin injection efficiency, the spin relaxation and related IREE mediated by interfacial states of TIs. [22,35] For experimental details about the THz-TDS setup, the readers may refer to Section S1, Supporting Information and ref.…”

Ultrafast spin-charge conversion at SnBi$_2$Te$_4$/Co topological insulator interfaces probed by terahertz emission spectroscopy

“…These experiments rely on ultrafast spin injection and their conversion into a charge current at TI material interfaces as explored recently for Bi/Bi 2 Te 3 systems [22]. THz emission TDS has proven to be a relevant experimental method [32][33][34] and is particularly important to probe the spin injection efficiency, the spin relaxation and related IREE mediated by interfacial states of TIs [22,35]. For experimental details about the THz-TDS setup, the readers may refer to Suppl.…”

THz emission from Fe/Pt spintronic emitters with L10-FePt alloyed interface

“…The THz emission from these spintronic THz emitters (STE) has remarkable properties in terms of signal strength and bandwidth; they are easy to use, robust, and do not require electrical connections. Their potential for technological applications is large, while the rich physics behind the excitation and emission has attracted scientific attention ( Agarwal et al., 2021 ; Hawecker et al., 2021 ; Zhang et al., 2020 ; Hoppe et al., 2021 ). During the last years, THz spintronic emitters have been heavily investigated aiming to obtain large signals and spectral bandwidths and to incorporate them into THz applications ( Papaioannou and Beigang, 2021 ; Bull et al., 2021 ; Wu et al., 2021 ).…”

“…In particular, a wide range of material properties have been studied including: different material compositions of FM/NM layers with a variety of thicknesses ( Torosyan et al., 2018 ; Seifert et al., 2016 ; Wu et al., 2017 ; Yang et al., 2016 ; Qiu et al., 2018 ), ferrimagnetic/NM structures ( Seifert et al., 2017 ; Schneider et al., 2018 , 2019 ; Fix et al., 2020 ), and antiferromagnetic metal/NM ( Ogasawara et al., 2020 ). In addition, the impact of material interfaces was studied by inserting non-magnetic interlayer material such as Cu,Al, Ti, Au, and ZnO layers in FM/X/NM trilayers ( Gueckstock et al., 2021 ; Papaioannou et al., 2018 ; Seifert et al., 2018 ; Hawecker et al., 2021 ; Li et al., 2018 ). Furthermore, the role of interface engineering at the FM/NM interface was examined ( Sasaki et al., 2017 ; Li et al., 2019 ; Nenno et al., 2019 ).…”