Large enhancement of the spin Hall effect in Au by side-jump scattering on Ta impurities

Abstract

We present measurements of the Spin Hall Effect (SHE) in AuW and AuTa alloys for a large range of W or Ta concentrations by combining experiments on lateral spin valves and FerromagneticResonance/spin pumping technique. The main result is the identification of a large enhancement of the Spin Hall Angle (SHA) by the side-jump mechanism on Ta impurities, with a SHA as high as + 0.5 (i.e 50%) for about 10% of Ta. In contrast the SHA in AuW does not exceed + 0.15 and can be explained by intrinsic SHE of the alloy without significant extrinsic contribution from skew or side-jump scattering by W impurities. The AuTa alloys, as they combine a very large SHA with a moderate resistivity (smaller than 85 µΩ.cm), are promising for spintronic devices exploiting the SHE.A goal of spintronics is to generate, manipulate and detect spin currents for the transfer and manipulation of information, thus allowing faster and low-energy consuming operations. Since the discovery of the Giant Magnetoresistance a "classical" way to produce spin currents was to take advantage of ferromagnetic materials and their two different spin channel conductivities [1,2]. In the last decade the rediscovery and study of spin orbit interaction effects brought new insights into creation mechanisms of spin currents. Among all mechanisms the spin Hall effect (SHE) focused a lot of attention as it allows the generation of spin currents from charge current and vice versa [3]. Despite being observed only a decade ago [4-6] these effects are already ubiquitous within the Spintronics as standard spin-current generators and detectors [7][8][9]. The conversion coefficient between charge and spin currents is called the spin Hall angle (SHA) and is defined as Θ SHE = ρ xy /ρ xx , ratio of the non-diagonal and diagonal terms of the resistivity tensor. One of the main interests of the SHE is to provide a new paradigm for Spintronics where non-magnetic materials becomes active spin current source and detector.Until now most of the reports focused on single heavy metals and intrinsic SHE mechanisms, the main materials of interest being: Pt, Ta, W, and some oxydes. With intrinsic mechanisms the SHA is typically proportional to the resistivity of the heavy metal, and generally, a large value of the SHA is associated with a high resistivity (i.e. -0.3 for the SHA in β − W is associated with 263 µΩ.cm [10]) which limits the current density and the resulting spin transfer torques on the magnetisation of an adjacent metallic ferromagnetic material. Extrinsic SHE mechanisms associated with the spin dependent scattering on impurities or defects are an alternative to generate transverse spin currents [11]. Two particular scattering mechanisms have been identified: the skew scattering [12] providing a non-diagonal term of the resistivity tensor proportional to the longitudinal resistivity (ρ xy ∝ ρ xx ) and the side jump [13] for which the non-diagonal term is proportional to the square of the resistivity (ρ xy ∝ ρ 2 xx ). For instance, the skew scattering mechanism have been o...

Large Multidirectional Spin-to-Charge Conversion in Low-Symmetry Semimetal MoTe2 at Room Temperature

“…On the one hand, we find that, for 2 values similar or longer than the thickness of MoTe2 (11 nm), | | tends to a low constant value independent of 2 , because the SCC process is limited by the MoTe2 thickness. This behavior allows us to get a lower limit for | |, which for the case of the conventional component is | | ≥ 0.21 at room temperature, comparable to the best known spin Hall metals 24,25 and alloys 23,44 . The lower limit for the unconventional component efficiency is also found to be remarkably large (| | ≥ 0.10), and with opposite sign, at room temperature.…”

Current‐Induced Spin–Orbit Torques for Spintronic Applications

“…Based on the SOT mechanisms, numerous material combinations of NM/FM structures have been investigated to improve spin Hall angle or SOT efficiency. For example, SHE can be enhanced by introducing scattering centers into NMs using methods of structural modification, [23,45,47,60,[91][92][93][94] alloying, [77,[95][96][97] or oxygen incorporation. [78,81,[98][99][100][101][102][103] The enhancement in the SOT efficiency has also been demonstrated by the modification of NM/FM interface, which increases REEinduced spin current and associated SOT, and/or improves the spin transmission through the interface.…”

“…Since the SHE and REE are based on SOC, much effort has been made to find material structures with strong SOC or a large θ SH . In this respect, heavy metals (HMs) such as Ta, [20,21,23,45,124] W, [22,47,48,73,125] and Pt [19,25,44,76,82,93,126,127] and their alloys [77,[95][96][97] have been extensively investigated. In addition, other exotic materials including topological insulators (TIs) [56,[128][129][130][131][132][133][134] or 2D materials [135][136][137][138][139][140][141] have been suggested as effective spin current sources.…”

“…This can be explained by the intrinsic SHE, in which θ SH is proportional to the resistivity. [22,44,76,82,93,97,145] However, it is difficult to unveil the correlation between the HM resistivity and the θ SH before performing more systematic studies using the same material. Moreover, when designing the material structure for a SOT device, it should be considered that a high resistive material is unfavorable for applications because of large energy consumption due to Joule heating.…”

Compared Efficiencies of Conversions between Charge and Spin Current by Spin-Orbit Interactions in Two- and Three-Dimensional Systems

“…We note that there are experimental evidences of the advantage of TI for the production of electrical power in spin-Seebeck-based devices. (where h rf is the magnetic rf field) by ISHE (Au [25], Pt [19], Au 0.97 W 0.07 [25], Au 0.975 Ta 0.025 [26]) or IEE (Ag/Bi [5] and Ag/α-Sn [9]) in experiments of spin pumping ferromagnetic resonance at room temperature. The results are obtained in the same setup ( f ∼ 9.7 GHz) and with the same geometry (i.e., width of 0.4 mm).…”