Search

Manganites have shown potential in spintronics because they exhibit high spin polarization. Here, by ferromagnetic resonance we have studied the damping properties of La0.67Sr0.33MnO3/Pt bilayers which are prepared by oxide molecular beam epitaxy. The damping coefficient (α) of a La0.67Sr0.33MnO3 (LSMO) single layer is found to be 0.0104. However the LSMO/Pt bilayers exhibit a decrease in α with an increase in Pt thickness. This decrease in the value of α is probably due to high anti-damping like torque. Furthermore, we have investigated the angle dependent inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other spin rectification effects such as the anomalous Hall effect and anisotropic magnetoresistance. We have observed a high spin pumping voltage (∼20 μV). The results indicate that both anti-damping and spin pumping phenomena occur simultaneously.

The spin Hall effect (SHE) is usually observed as a bulk effect in high-symmetry crystals with substantial spin–orbit coupling (SOC), where the symmetric spin–orbit field imposes a widely encountered trade-off between spin Hall angle (θSH) and spin diffusion length (Lsf), and spin polarization, spin current and charge current are constrained to be mutually orthogonal. Here, we report a large θSH of 0.32 accompanied by a long Lsf of 2.2 μm at room temperature in a low-symmetry few-layered semimetal MoTe2, thus identifying it as an excellent candidate for simultaneous spin generation, transport and detection. In addition, we report that longitudinal spin current with out-of-plane polarization can be generated by both transverse and vertical charge current, due to the conventional and a newly observed planar SHE, respectively. Our study suggests that manipulation of crystalline symmetries and strong SOC opens access to new charge-spin interconversion configurations and spin–orbit torques for spintronic applications. A large spin Hall angle and long spin diffusion length are found in the low-symmetry, few-layer semimetal MoTe2 at room temperature, thus identifying this material as an excellent candidate for simultaneous spin generation, transport and detection.

It is now well established that the peculiar linear-in-momentum dependence of the Rashba (and of the Dresselhaus) spin-orbit coupling leads to the vanishing of the spin Hall conductivity in the bulk of a two-dimensional electron gas (2DEG). In this paper we discuss how generic magnetic couplings change this behaviour providing then a potential handle on the spin Hall effect. In particular we examine the influence of magnetic impurities and an in-plane magnetic field. We find that in both cases there is a finite spin Hall effect and we provide explicit expressions for the spin Hall conductivity. The results can be obtained by means of the quasiclassical Green function approach, that we have recently extended to spin-orbit coupled electron systems.

Spin Hall effect (SHE) is the generation of spin current due to an electric field, and has been observed in a variety of materials. The analogous spin Hall current can be induced by chemical potential and temperature gradient, both of which are present in hot and dense nuclear matter created in heavy-ion collisions. In this letter, we investigate the perspective of detecting spin Hall current experimentally. We propose to measure "directed spin flow", the first Fourier coefficients of local spin polarization of $\Lambda$ ($\bar{\Lambda}$) hyperon, at central collisions to probe spin Hall current. To quantify induced spin current, we evaluate relevant transport coefficients using thermal field theory. We benchmark the magnitude of the induced "directed spin flow" at two representatively collisions energies, namely $\sqrt{s}_{NN}=200~{\rm GeV}$ and $\sqrt{s}_{NN}=19.6~{\rm GeV}$, by employing a phenomenologically motivated freeze-out prescription. At both beam energies, the resulting "directed spin flow" ranges from $10^{-4}$ to $10^{-3}$, and is very sensitive to the rapidity., Comment: 8 pages, 4 figures; published version

Determining the detailed spin texture of topological surface states is important when one wants to apply topological insulators in spintronic devices. In principle, the in-plane spin component of the surface states can be measured by a method analogous to the so-called Meservey-Tedrow technique. In the present work we suggest that the out-of-plane spin component can be determined by spin Hall effect tunneling spectroscopy. We derive an analytical formula that allows to extract the out-of-plane spin component from spin Hall effect tunneling spectra. We test our formula using realistic tight-binding models of Bi$_2$Se$_3$ and Sb$_2$Te$_3$. We demonstrate that the extracted out-of-plane spin polarization is in very good agreement with the actual out-of-plane spin polarization.

The authors demonstrate the magnetization dependent spin Hall effect where the spin polarization of pure spin current can be additionally manipulated by the magnetization.

In an easy-plane antiferromagnet with the Dzyaloshinskii–Moriya interaction (DMI), magnons are subject to an effective spin-momentum locking. An in-plane temperature gradient can generate interfacial accumulation of magnons with a specified polarization, realizing the magnon thermal Edelstein effect. We theoretically investigate the injection and detection of this thermally driven spin polarization in an adjacent heavy metal with a strong spin Hall effect. We find that the inverse spin Hall voltage depends monotonically on both temperature and the DMI but non-monotonically on the hard-axis anisotropy. Counterintuitively, the magnon thermal Edelstein effect is an even function of a magnetic field applied along the Neel vector.

We report an unconventional quantum spin Hall phase in the monolayer WTe2, which exhibits hitherto unknown features in other topological materials. The low symmetry of the structure induces a canted spin texture in the yz plane, which dictates the spin polarization of topologically protected boundary states. Additionally, the spin Hall conductivity gets quantized (2e2/h) with a spin quantization axis parallel to the canting direction. These findings are based on large-scale quantum simulations of the spin Hall conductivity tensor and nonlocal resistances in multiprobe geometries using a realistic tight-binding model elaborated from first-principle methods. The observation of this canted quantum spin Hall effect, related to the formation of topological edge states with nontrivial spin polarization, demands for specific experimental design and suggests interesting alternatives for manipulating spin information in topological materials., M. V. acknowledges support from “La Caixa” Foundation and the Centre for Advanced 2D Materials at the National University of Singapore for its hospitality. X. W. acknowledges the ANR Flagera GRANSPORT funding. ICN2 authors were supported by the European Union Horizon 2020 research and innovation programme under Grant Agreement No. 881603 (Graphene Flagship) and No. 824140 (TOCHA, H2020-FETPROACT-01-2018). ICN2 is funded by the CERCA Programme/Generalitat de Catalunya, and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV2017-0706). V. M. P. acknowledges the support of the National Research Foundation (Singapore) under its Medium-Sized Centre Programme (R-723-000-001-281).

The spin Hall effect of light originates from spin-orbit interaction of light, which manifests two types of geometric phases. In this paper, we report the observation of a geometric spin Hall effect by generating a light beam with inhomogeneous polarization distribution. Unlike the previously reported geometric spin Hall effect observed in a tilted beam-detector system, which is believed to result from an effective spin-redirection Berry geometric phase, the geometric spin Hall effect demonstrated here is attributed to an effective, spatially varying Pancharatnam-Berry geometric phase generated by the inhomogeneous polarization geometry. Our further experiments show that the geometric spin Hall effect can be tuned by tailoring the polarization geometry of light, demonstrating the spin states of photons can be steered with a great flexibility.

We study the mechanisms of the spin Hall effect (SHE) and anomalous Hall effect (AHE) in 3$d$ ferromagnetic metals (Fe, Co, permalloy (Ni$_{81}$Fe$_{19}$; Py), and Ni) by varying their resistivities and temperature. At low temperatures where the phonon scattering is negligible, the skew scattering coefficients of the SHE and AHE in Py are related to its spin polarization. However, this simple relation breaks down for Py at higher temperatures as well as for the other ferromagnetic metals at any temperature. We find that, in general, the relation between the SHE and AHE is more complex, with the temperature dependence of the SHE being much stronger than that of AHE., 7 pages, 5 figures

The miniaturization of complementary metal–oxide–semiconductor (CMOS) devices becomes increasingly difficult due to fundamental limitations and the increase of leakage currents. Large research efforts are devoted to find alternative concepts that allow for a larger data-density and lower power consumption than conventional semiconductor approaches. Spin waves have been identified as a potential technology that can complement and outperform CMOS in complex logic applications, profiting from the fact that these waves enable wave computing on the nanoscale. The practical application of spin waves, however, requires the demonstration of scalable, CMOS compatible spin-wave detection schemes in material systems compatible with standard spintronics as well as semiconductor circuitry. Here, we report on the wave-vector independent detection of short-waved spin waves with wavelengths down to 150 nm by the inverse spin Hall effect in spin-wave waveguides made from ultrathin Ta/Co8Fe72B20/MgO. These findings open up...

Spin circuits with four component voltages and currents have been developed and used in the past to analyze various structures, which include non-collinear ferromagnets. Recent demonstrations of large spin orbit torques in heavy metals like Pt, Ta, and W open up new possibilities in spintronic applications by providing an alternative way to write information into a magnet. Here, we extend the four component (one charge and three spins) conductance matrix to include materials with spin Hall effect based on the standard diffusion equation. Our proposed spin circuit successfully reproduces standard results like spin Hall effect (SHE), inverse spin Hall effect, and spin Hall magnetoresistance. This circuit representation also makes it straightforward to analyze new configurations. We present two examples, namely, 1) the possibility of spin injection using giant SHE (GSHE) materials into semiconductors without tunneling barriers, and 2) the effect of spin ground on one surface to enhance spin current injection from the opposite surface in a thin GSHE sample. Finally, we provide an elemental conductance matrix for a small cubic structure which can be used as a building block to analyze any arbitrarily shaped GSHE material.

Tunable spin transport in nanodevices is highly desirable to spintronics. Here, we predict existence of quantum spin Hall effects and tunable spin transport in As-graphane, based on first-principle density functional theory and tight binding calculations. Monolayer As-graphane is constituted by using As adsorbing on graphane with honeycomb H vacancies. Owing to the surface strain, monolayer As-graphane nanoribbons will self-bend toward the graphane side. The naturally curved As-graphane nanoribbons then exhibit unique spin transport properties, distinctively different from the flat ones, which is a two-dimensional topological insulator. Under external stress, one can realize tunable spin transport in curved As-graphane nanoribon arrays. Such intriguing mechanical bending induced spin flips can offer promising applications in the future nanospintronics devices.

Electrical injection of spin current via the spin Hall effect has a huge technological implication for spin transfer torque devices and in magnon spintronics. This effect generates a spin current perpendicular to a charge current but has so far relied on expensive heavy metals. This paper uncovers a new mechanism present in ferromagnets, the anomalous spin Hall effect, where the magnetization of the ferromagnet is used to tune the spin injection efficiency up to a level greater than that found in heavy metals. The authors demonstrate this anomalous mechanism via an experimental advance where nonlocal magnon transport in a ferrimagnetic insulator (YIG) was achieved using a ferromagnetic metal (permalloy) for efficient and tunable electrical injection and detection of magnons.

The inverse spin Hall effect (ISHE) has been detected and separated from spin rectification effect (SRE) by inverting spin injection direction in metallic system. This work is based on the relation between the two effects and the spin injection direction: the sign of VISHE changes because of the reversing direction of spin injection while the VSRE is independent on it. According to the different voltage signals before and after the spin injection inverted, the pure VISHE and VSRE are calculated by utilizing the method of addition and subtraction. The signals can be separated in a wide range of frequency and power.

Three-dimensional (3D) topological insulators are known for their strong spin-orbit coupling (SOC) and the existence of spin-textured surface states that might be potentially exploited for "topological spintronics." Here, we use spin pumping and the inverse spin Hall effect to demonstrate successful spin injection at room temperature from a metallic ferromagnet (CoFeB) into the prototypical 3D topological insulator Bi2Se3. The spin pumping process, driven by the magnetization dynamics of the metallic ferromagnet, introduces a spin current into the topological insulator layer, resulting in a broadening of the ferromagnetic resonance (FMR) line width. Theoretical modeling of spin pumping through the surface of Bi2Se3, as well as of the measured angular dependence of spin-charge conversion signal, suggests that pumped spin current is first greatly enhanced by the surface SOC and then converted into a dc-voltage signal primarily by the inverse spin Hall effect due to SOC of the bulk of Bi2Se3. We find that the FMR line width broadens significantly (more than a factor of 5) and we deduce a spin Hall angle as large as 0.43 in the Bi2Se3 layer.

This chapter describes an experiment on the inverse spin Hall effect (ISHE) induced by spin pumping. Spin pumping is the generation of spin currents as a result of magnetization M(t) precession; in a ferromagnetic/paramagnetic bilayer system, a conduction-electron spin current is pumped out of the ferromagnetic layer into the paramagnetic conduction layer in a ferromagnetic resonance condition. The sample used in the experiment is a Ni81Fe19/Pt bilayer film comprising a 10-nm-thick ferromagnetic Ni81Fe19layer and a 10-nm-thick paramagnetic Pt layer. For the measurement, the sample system is placed near the centre of a TE011 microwave cavity at which the magnetic-field component of the microwave mode is maximized while the electric-field component is minimized.

The needs of high speed performance electronic devices for various applications require novel materials and new physical phenomena. For these purposes we propose to study new physical effects based on electron scattering on magnetic skyrmions and vortices distributed in a 2D ferromagnetic material. We show that the topological spin Hall effect can be efficiently employed for the filtering, switching, and separation of spin currents. For some values of the parameters (conduction electron concentrations, and skyrmion/vortex sizes) it is possible to separate Hall currents for different electron spin projections as it is like for different carrier charges (electrons and holes) in the normal Hall effect. The calculations are performed using the Boltzmann kinetic equation for the nonequilibrium distribution function and the Lippmann-Schwinger equation for the transition matrix in the whole range of the adiabaticity parameter. The spin filtering due to the skyrmion/vortex scattering can be several orders of magnitude more efficient in the narrow range of the electron concentrations than that of the ordinary ferromagnetic spin polarization in spintronics.

Understanding the evolution of spin-orbit torque (SOT) with increasing heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical for the development of magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and dampinglike SOT regarding their dependence on NM thickness. Here, using linewidth and phase-resolved amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract damping enhancement and both fieldlike and dampinglike inverse SOT in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$/Pt bilayers as a function of Pt thickness. By enforcing an interpretation of the data which satisfies Onsager reciprocity, we find that both the damping enhancement and dampinglike inverse SOT can be described by a single spin diffusion length $(\ensuremath{\approx}4\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$, and that we can separate the spin pumping and spin-memory loss contributions to the total damping. This analysis indicates that less than 40% of the angular momentum pumped by FMR through the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$/Pt interface is transported as spin current into the Pt. On account of the spin-memory loss and corresponding reduction in total spin current available for spin-charge transduction in the Pt, we determine the Pt spin Hall conductivity $[{\ensuremath{\sigma}}_{\mathrm{SH}}=(2.36\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.28em}{0ex}}{\ensuremath{\omega}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}]$ and bulk spin Hall angle $({\ensuremath{\theta}}_{\mathrm{SH}}=0.387\ifmmode\pm\else\textpm\fi{}0.008)$ to be larger than commonly cited values. These results suggest that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize spin loss. Lastly, we find that self-consistent fitting of the damping and SOT data is best achieved by a model with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such that both the spin diffusion length and spin Hall conductivity are proportional to the Pt charge conductivity.

Spin transport and distribution of spin accumulation in CuPt/Fe heterostructure are numerically investigated, using linearized Levy-Fert model. It was shown that Spin Hall Effect in CuPt layer produces non-equilibrium spin accumulation in adjacent ferromagnetic layer. Spin accumulation vector is not collinear with the direction of magnetization in ferromagnetic layer which leads to the appearance of spin transfer torque. The absolute values and angular dependence of this torque were calculated and it was demonstrated that for the current the values of torques are sufficient for manipulation of magnetization of ferromagnetic layer.

We demonstrate spin pumping and inverse spin Hall effect (ISHE) in an all oxide heterostructure composed of two oxides with different respective crystal structures. Y3Fe5O12 (YIG) is used as a spin source, being a perfect candidate because of its low damping and insulating behavior. SrRuO3 (SRO), a perovskite oxide with metallic conductivity, serves as a spin sink. Spin pumping is shown by the increase of the damping in ferromagnetic resonance for the YIG in the presence of an SRO top layer and by the inverse spin Hall effect appearing in the SRO. Transmission electron microscopy shows that the growth of YIG is fully epitaxial, while the SRO grows in islands of several polycrystaline phases, a fact which strongly influences the measured ISHE. The magnetization of the YIG remains unaffected by the SRO layer while the SRO no longer shows the low temperature ferromagnetism typically observed in monocrystalline layers.

We consider the spin-orbit-induced spin Hall effect and spin swapping in diffusive superconductors. By employing the nonequilibrium Keldysh Green's function technique in the quasiclassical approximation, we derive coupled transport equations for the spectral spin and particle distributions and for the energy density in the elastic scattering regime. We compute four contributions to the spin Hall conductivity, namely, skew scattering, side jump, anomalous velocity, and the Yafet contribution. The reduced density of states in the superconductor causes a renormalization of the spin Hall angle. We demonstrate that all four of these contributions to the spin Hall conductivity are renormalized in the same way in the superconducting state. In its simplest manifestation, spin swapping transforms a primary spin current into a secondary spin current with swapped current and polarization directions. We find that the spin-swapping coefficient is not explicitly but only implicitly affected by the superconducting gap through the renormalized diffusion coefficients. We discuss experimental consequences for measurements of the (inverse) spin Hall effect and spin swapping in four-terminal geometries. In our geometry, below the superconducting transition temperature, the spin-swapping signal is increased an order of magnitude while changes in the (inverse) spin Hall signal are moderate. © 2017 American Physical Society

In this work we address optical orientation, a process consisting in the excitation of spin polarized electrons across the gap of a semiconductor. We show that the combination of optical orientation with spin-dependent scattering leading to the inverse spin-Hall effect, i.e., to the conversion of a spin current into an electrical signal, represents a powerful tool to generate and detect spin currents in solids. We consider a few examples where these two phenomena together allow addressing the spin-dependent transport properties across homogeneous samples or metal/semiconductor Schottky junctions.

Topological crystalline insulator SnTe is a promising material for future spintronics applications because of the strong spin-orbit coupling and surface states protected by the mirror symmetry of the crystal. In this paper, using a high-quality epitaxial (001)-oriented Fe/SnTe/CdTe/ZnTe heterostructure grown on GaAs, we successfully observe the inverse spin Hall effect in SnTe induced by spin pumping, which is confirmed by detailed analyses of the dependence of the electromotive force on the microwave power, magnetic-field angle, and temperature. By a rough estimation, a relatively large spin Hall angle of \ensuremath{\sim}0.01 is obtained for bulk SnTe at room temperature. This large value may be partially caused by the surface states. Our result suggests that SnTe can be used for efficient spin-charge current conversion.

2nd EditionNew edition, updated to include key findings made in the past 10 yearsIntegrates the physics of transport phenomena and elementary magnetism in semiconductors; This book offers an extensive introduction to the extremely rich and intriguing field of spin-related phenomena in semiconductors. In this second edition, all chapters have been updated to include the latest experimental and theoretical research. Furthermore, it covers the entire field: bulk semiconductors, two-dimensional semiconductor structures, quantum dots, optical and electric effects, spin-related effects, electron-nuclei spin interactions, Spin Hall effect, spin torques, etc. Thanks to its self-contained style, the book is ideally suited for graduate students and researchers new to the field.

A two-dimensional electron gas emerged at a LaAlO3/SrTiO3 interface is an ideal system for “spin–orbitronics” as the structure itself strongly couple the spin and orbital degree of freedom through the Rashba spin–orbit interaction. One of core experiments toward this direction is the nonlocal spin transport measurement, which has remained elusive due to the low spin injection efficiency to this system. Here we bypass the problem by generating a spin current not through the spin injection from outside but instead through the inherent spin Hall effect and demonstrate the nonlocal spin transport. The analysis on the nonlocal spin voltage, confirmed by the signature of a Larmor spin precession and its length dependence, displays that both D’yakonov–Perel’ and Elliott–Yafet mechanisms involve in the spin relaxation at low temperature. Our results show that the oxide heterointerface is highly efficient in spin-charge conversion with exceptionally strong spin Hall coefficient γ ∼ 0.15 ± 0.05 and could be an outs...

We systematically measure and analyze the spin diffusion length and the spin Hall effect in Pt with a wide range of conductivities using the spin absorption method in lateral spin valve devices. We observe a linear relation between the spin diffusion length and the conductivity, evidencing that the spin relaxation in Pt is governed by the Elliott-Yafet mechanism. We find a single intrinsic spin Hall conductivity ($\sigma_{SH}^{int}=1600\pm150\: \Omega^{-1}cm^{-1}$) for Pt in the full range studied which is in good agreement with theory. For the first time we have obtained the crossover between the moderately dirty and the superclean scaling regimes of the spin Hall effect by tuning the conductivity. This is equivalent to that obtained for the anomalous Hall effect. Our results explain the spread of the spin Hall angle values in the literature and find a route to maximize this important parameter., Comment: 11 pages, 4 figures

Here we report the measurement of the interfacial spin accumulation induced by the spin Hall effect in Pt and W thin films using magneto-optical Kerr microscopy. We show that the Kerr rotation has opposite sign in Pt and W and scales linearly with current density. By comparing the experimental results with ab-initio calculations of the spin Hall and magneto-optical Kerr effects, we quantitatively determine the current-induced spin accumulation at the Pt interface as $5*10^{-12} \mu_B$A$^{-1}$cm$^2$ per atom. From thickness-dependent measurements, we determine the spin diffusion length in a single Pt film to be $11 \pm 3$ nm, which is significantly larger compared to that of Pt adjacent to a magnetic layer., Comment: 16 pages including Supplemental Material

Inverse spin Hall effect (ISHE) has been intensively investigated by injecting a spin current from ferromagnet (FM) to normal metal (NM) with large spin-orbit-coupling (SOC) and simultaneously detecting the induced electrical current.