Tuning Spin Hall Angles by Alloying

Obstbaum, Martin; Decker, Martin; Greitner, A. K.; Haertinger, M.; Meier, Thomas; Kronseder, M.; Chadova, Kristina; Wimmer, Sebastian; Ködderitzsch, D.; Ebert, H.; Back, Christian

doi:10.1103/physrevlett.117.167204

Cited by 110 publications

(97 citation statements)

References 44 publications

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“…See Supplementary Materials [37] for more information on the samples and experimental methods. grown Pt/FM samples are comparable to those reported from damping measurements on similar structures in the literature [9,11,13,16,24,38]. However, all of these values of eff,α ↑↓ are markedly larger than the expected value eff ↑↓ =0.31×10 15 Ω -1 m -2 as calculated with Eq.…”

supporting

confidence: 88%

“…Interfacial spin transport is at the root of many spintronic phenomena, e.g. spin-orbit torques (SOTs) [1,2], spin magnetoresistance (SMR) [3,4], the spin Seebeck effect (SSE) [5][6][7], and spin pumping [8][9][10][11][12][13][14][15][16] in heavy-metal /ferromagnet (HM/FM) systems. The key factor determining the spin transmission and spin backflow (SBF) of a HM/FM interface [17,18] is the effective spin-mixing conductance [19] eff ↑↓ = HM/FM ↑↓ /(1+2 HM/FM ↑↓ /GHM) (1) where HM/FM ↑↓ is the bare interfacial spin-mixing conductance, GHM = 1/λsρxx, ρxx, and λs are the spin conductance, the resistivity, and the spin diffusion length of the HM layer, respectively.…”

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confidence: 99%

“…The key factor determining the spin transmission and spin backflow (SBF) of a HM/FM interface [17,18] is the effective spin-mixing conductance [19] eff ↑↓ = HM/FM ↑↓ /(1+2 HM/FM ↑↓ /GHM) (1) where HM/FM ↑↓ is the bare interfacial spin-mixing conductance, GHM = 1/λsρxx, ρxx, and λs are the spin conductance, the resistivity, and the spin diffusion length of the HM layer, respectively. In inverse spin Hall effect (ISHE) experiments where spin currents are generated by spin pumping or the SEE, the measured voltage signals are proportional to eff ↑↓ θSH [6][7][8][9][10][11][12][13][14][15][16]. Here θSH is the spin Hall ratio of the HM.…”

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confidence: 99%

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Effective Spin-Mixing Conductance of Heavy-Metal–Ferromagnet Interfaces

2019

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The effective spin-mixing conductance ( eff ↑↓ ) of a heavy metal/ferromagnet (HM/FM) interface characterizes the efficiency of the interfacial spin transport. Accurately determining eff ↑↓ is critical to the quantitative understanding of measurements of direct and inverse spin Hall effects. eff ↑↓ is typically ascertained from the inverse dependence of magnetic damping on the FM thickness under the assumption that spin pumping is the dominant mechanism affecting this dependence. Here we report that, this assumption fails badly in many in-plane magnetized prototypical HM/FM systems in the nm-scale thickness regime. Instead, the majority of the damping is from two-magnon scattering at the FM interface, while spin-memory-loss scattering at the interface can also be significant. If these two effects are neglected, the results will be an unphysical "giant" apparent eff ↑↓ and hence considerable underestimation of both the spin Hall ratio and the spin Hall conductivity in inverse/direct spin Hall experiments.

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confidence: 88%

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confidence: 99%

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Effective Spin-Mixing Conductance of Heavy-Metal–Ferromagnet Interfaces

2019

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“…The intrinsic mechanism from Berry curvature in the conduction band gives the same dependence ρ xy ∝ ρ 2 xx as the side-jump contribution so that, for example the SHE of AuPt (SHA=0.3 at max.) alloys could be explained by a predominant intrinsic effect rather than ascribed to sidejump [16].In this letter we present a study of Au-based alloys with W and T a impurities. We demonstrate that the side-jump scattering mechanism dominates in AuTa alloys, and generates high spin Hall angles (up to + 0.5) with the additional advantage of resistivities (ρ AuT a < 85µΩ.cm) smaller than in most materials with SHA in the same range.…”

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

Laczkowski

Yang

et al. 2017

Phys. Rev. B

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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...

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“…Among all HMs, 5d transition metals such as Pt [14], β-Ta [5], and β-W [15] shown that 5d HM-related alloys and oxides can generate sizable SHE and even possess greater spin Hall ratios than pure HMs. For instance, Hf(Al)-doped Pt [16], Au-doped Pt [17], PtMn [18], W-doped Au [19], and WOx [20] all show larger spin Hall ratios or DL  while compare to their pure HM counterparts. Even by oxidizing or doping dopants into light transition metals such as Cu, the spin Hall ratio can be significantly enhanced [21,22].…”

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Tunable spin-orbit torque in Cu-Ta binary alloy heterostructures

Chen¹,

Wu²,

Yen³

et al. 2017

Phys. Rev. B

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The spin Hall effect (SHE) is found to be strong in heavy transition metals (HM), such as Ta and W, in their amorphous and/or high resistivity form. In this work, we show that by employing a CuTa binary alloy as buffer layer in an amorphous Cu100-xTax-based magnetic heterostructure with perpendicular magnetic anisotropy (PMA), the SHE-induced damping-like spin-orbit torque (DL-SOT) efficiency DL  can be linearly tuned by adjusting the buffer layer resistivity. Currentinduced SOT switching can also be achieved in these Cu100-xTax-based magnetic heterostructures, and we find the switching behavior better explained by a SOT-assisted domain wall propagation picture. Through systematic studies on Cu100-xTax-based samples with various compositions, we determine the lower bound of spin Hall conductivity

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Tuning Spin Hall Angles by Alloying

Cited by 110 publications

References 44 publications

Effective Spin-Mixing Conductance of Heavy-Metal–Ferromagnet Interfaces

Effective Spin-Mixing Conductance of Heavy-Metal–Ferromagnet Interfaces

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

Tunable spin-orbit torque in Cu-Ta binary alloy heterostructures

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