Inverse Spin Hall Effect Research Articles

Impact of spin-flip scattering on spin current and inverse Spin-Hall effect in silicon doped by bismuth, antimony or phosphorus

The influence of spin-flip scattering on the generation of spin currents in n-type silicon is studied. Doping of silicon by heavy donors, such as bismuth or antimony, leads to an additional spin scattering of conduction electrons on the impurity-induced spin-orbit potential. Based on the diffusion model and the theory of spin pumping spin current and inverse-spin-Hall effect voltage are considered for different types of donors with various concentrations and spin diffusion lengths. Calculations yield the dependence of the inverse spin-Hall effect signal on the parameters of bismuth-doped silicon layers and also explain the absence of such signal for silicon layers doped by phosphorus or antimony.

Ultrafast spin-to-charge conversion in antiferromagnetic (111)-oriented L12-Mn3Ir

Antiferromagnetic L12-Mn3Ir combines outstanding spin-transport properties with magnons in the terahertz (THz) frequency range. However, the THz radiation emitted by ultrafast spin-to-charge conversion via the inverse spin Hall effect remains unexplored. In this study, we measured the THz emission and transmission of a Permalloy/(111)-oriented L12-Mn3Ir multilayer by THz time-domain spectroscopy. The spin Hall angle was determined to be approximately constant at 0.035 within a frequency range of 0.3–2.2 THz, in comparison with the THz spectroscopy of a Permalloy/Pt multilayer. Our results not only demonstrate the potential of L12-Mn3Ir as a spintronic THz emitter but also provide insights into the THz spin transport properties of L12-Mn3Ir.

Significant efficiency increment of spintronic terahertz emitters by oxygen engineering

Spintronic terahertz (THz) emitters have been intensively explored as next-generation sources of THz waves due to their low-cost, nanometer thickness, and broadband spectra. Growing research works are focusing on how to improve the THz emission efficiency, mainly by using a larger spin-Hall angle heavy metal. Currently, the highest intensity spintronic THz emission was based on a CoFeB/Pt heterostructure. Here, we significantly improve the THz emission intensity of CoFeB/Pt by a factor up to 270% through simply incorporating oxygen atoms into the Pt layer. The oxidation of a Pt layer generates a large extrinsic spin Hall angle, which promotes the spin-to-charge conversion of PtOx. Furthermore, the oxygen incorporation also causes a finite oxidation of CoFeB near the interface. We revealed that the significantly enhanced THz emission of CoFeB/PtOx is contributed by both the bulk inverse spin Hall effect of PtOx and the interface effect. Finally, we demonstrated that the oxygen engineering procedure to improve the THz emission of spintronic THz emitters is a common phenomenon as verified in examples, including Co/PtOx, NiFe/PtOx, CoFeB/WOx, and CoFeB/TaOx heterostructures. These findings show that an oxidized heavy metal is a simple, low-cost, and effective route to enhance the spin-to-charge conversion and achieve intense THz pulses, which is promising especially for on-chip THz devices.

Spin pumping and inverse spin Hall effect in magnetron-sputtered large area MoS2/Co40Fe40B20 bilayers

Transition metal dichalcogenides (TMDs) are novel class of quantum materials which show potentials for optoelectronics, valleytronics, opto-valleytronics etc. TMDs are also found to exhibit high spin orbit coupling and therefore, they have been extensively studied for spin to charge conversion or spin pumping phenomena. The robustness of MoS2 and its high availability in nature as molybdenite, have made it a suitable candidate for device applications. Among all the methods designed to fabricate large area TMDs on industrially compatible substrates, the sputtering technique offers advantage to prepare large area films. Here we report the observation of spin to charge conversion in large area magnetron-sputtered MoS2 by inverse spin Hall effect (ISHE) via microwave driven ferromagnetic resonance spectroscopy. In the continuous MoS2/CoFeB thin films, angle dependent measurements of ISHE have been performed to identify various galvanometric rectification effects. The spin diffusion length, real part of spin mixing conductance and the electromotive force (emf) arising due to inverse spin Hall effect are found to be 7.83 ± 0.57 nm, (1.43 ± 0.019) × 1019 m−2 and 4.38 ± 0.12 μV, respectively. These results show that the MoS2 films exhibit high spin orbit coupling for spin to charge conversion physics and their relevance in SOT based applications.

Spin reorientation induced large spin memory loss at Py/Pd interface

Achieving spin current switching functionality is crucial for the development next-generation low power information storage. In this study, the spin reorientation and temperature dependence of spin Hall angle θSH in the Permalloy (Py)/Pd bilayer were investigated by using ferromagnetic resonance, spin pumping, inverse spin Hall effect, and quantum interference transport. The uniaxial ferromagnetic perpendicular magnetic anisotropy (PMA) induced by spin reorientation persists at the Py/Pd interface below 30 K. This PMA further enhances the interfacial spin scattering, leading to a reduction of injected spin current, as indicated by the underestimated θSH values. These experimental results demonstrate that the interfacial spin reorientation at the ferromagnet/heavy metal interface, commonly employed in spintronic devices, causes a significant spin memory loss effect. Our findings provide valuable insights into the influence of interlayer spin configuration on spin transport, which can be utilized in the rational design of spintronic devices based on pure spin current.

Spin-to-charge conversion in tantalum with structural phase transition

Tantalum (Ta), which is widely used as a spin sink material, especially for its β-phase with strong spin-orbit coupling (SOC) exhibits a high spin-charge interconversion efficiency. In this work, we investigate the spin-to-charge conversion (SCC) process of Ta/Permalloy (Ta/Py) bilayers with Ta having different crystalline phases. The structural phase transition of Ta film from tetragonal to body-centered cuboidal (BCC) which corresponds to β- and α-phases was obtained via high-temperature annealing in vacuum atmosphere. By applying ferromagnetic resonance (FMR) and inverse spin Hall effect (ISHE) measurements, the measured spin mixing conductance and SCC DC voltage show a strong correlation with the crystalline phase of Ta thin films in Ta/Py bilayers. A significant enhancement of spin mixing conductance in (β + α)-Ta/Py has been found and a higher SCC DC voltage was detected for α-phase Ta film with a weak SOC than β-phase Ta film with a strong SOC. These results reveal the significant role of the interfacial constitution in heavy metal/ferromagnet bilayers for spin current transportation, which can promote the development of high-efficiency spin-based devices through interfacial engineering.

An optimized growth model for Fe/Pt heteroepitaxy by computational and structural studies

Thin layers of ferromagnetic/non-magnetic bimetallic heterostructures have become the focal point of spintronics, primarily due to their capacity to convert spin to charge current, leveraging the spin- and inverse spin Hall effects. However, the interfacial properties and morphologies can significantly influence this conversion. Hence, we employed molecular dynamics calculations to model the construction of the Fe/Pt interface at various bilayer growth temperatures and Pt deposition rates. We then experimentally evaluated the modeling using x-ray methods to resolve the chemical and structural state of the interface. The calculations revealed moderate diffusive phenomena between the adjacent layers and an interfacial roughness of less than 1 nm, consistent with the experimental observations. In cases where plastic relaxation of the Fe/Pt interface is insufficient, lattice deformation is mitigated by a local pseudomorphic growth caused by transformation of the Pt crystal symmetry. Additionally, interfacial planar defects may emerge as a complementary stress-relieving mechanism to misfit dislocations. By combining the experimental and computational findings, we propose optimized growth conditions for an “ideal” Fe/Pt interface, which could serve as a useful tool to control the efficiency of spin-to-charge conversion.

Antiferromagnetic magnon spintronic based on nonreciprocal and nondegenerated ultra-fast spin-waves in the canted antiferromagnet α-Fe2O3.

Spin-waves in antiferromagnets hold the prospects for the development of faster, less power-hungry electronics and promising physics based on spin superfluids and coherent magnon condensates. For both these perspectives, addressing electrically coherent antiferromagnetic spin-waves is of importance, a prerequisite that has been so far elusive, because, unlike ferromagnets, antiferromagnets couple weakly to radiofrequency fields. Here, we demonstrate the detection of ultra-fast nonreciprocal spin-waves in the dipolar exchange regime of a canted antiferromagnet using both inductive and spintronic transducers. Using time-of-flight spin-wave spectroscopy on hematite (α-Fe2O3), we find that the magnon wave packets can propagate as fast as 20 kilometers/second for reciprocal bulk spin-wave modes and up to 6 kilometers/second for surface spin-waves propagating parallel to the antiferromagnetic Néel vector. We lastly achieve efficient electrical detection of nonreciprocal spin-wave transport using nonlocal inverse spin-Hall effects. The electrical detection of coherent nonreciprocal antiferromagnetic spin-waves paves the way for the development of antiferromagnetic and altermagnet-based magnonic devices.

Anomalous and inverse spin Hall effects in Pt1-xBix/(YLuBiCa)3(FeGa)5O12 heterojunction

A garnet film with spatial magnetic moment distribution has been grown on gadolinium gallium garnet wafer (111) crystal plane, by regulating liquid phase epitaxial growth parameters and sub-lattice ions substitution, then 10 nm Pt1-xBix (x = 2% – 8%) alloy film was deposited on the surface of the garnet films. A new spin heterojunction Pt1-xBix/(YLuBiCa)3(FeGa)5O12 with both inverse spin Hall effect (ISHE) and anomalous spin Hall effect (ASHE) was designed and fabricated. The spatial magnetic moment distribution of the heterojunction has been found, which lays the foundation of the spin heterojunction for multiple spin injection with both spin electron reverse injection and anomalous injection. Because Bi ions doping and substitution increases the spin–orbit torque and the mixed conductance of the heterojunction, an oblique ASHE voltage curve and an enhanced ISHE voltage curve with double resonance peak were observed. It was confirmed that the injection of spinning electron into the heterojunction can be enhanced with both the ISHE and ASHE effect by adjusting the spatial magnetic moment distribution, which is a foundation for the future application of spin wave 3D antenna and other devices.

Spin-to-Charge Conversion in All-Oxide La2/3Sr1/3MnO3/SrIrO3 Heterostructures.

Spin injection and spin-charge conversion processes in all-oxide La2/3Sr1/3MnO3/SrIrO3 (LSMO/SIO) heterostructures with different SIO layer thickness and interfacial features have been studied. Ferromagnetic resonance (FMR) technique has been used to generate pure spin currents by spin pumping (SP) in ferromagnetic (FM) half-metallic LSMO. The change of the resonance linewidth in bare LSMO layers and LSMO/SIO heterostructures suggests a successful spin injection into the SIO layers. However, low values of the spin mixing conductance, compared to more traditional permalloy (Py)/Pt or yttrium iron garnet (YIG)/Pt systems, are found. A thorough analysis of the interfaces by high-resolution scanning transmission electron microscopy (HR-STEM) imaging suggests that they are structurally clean and atomic sharp, but a compositional analysis by energy-dispersive X-ray spectroscopy (EDS) reveals the interdiffusion of La, Ir, and Mn atomic species in the first atomic layers close to the interface. Inverse spin Hall effect (ISHE) measurements evidence that interfacial features play a very relevant role in controlling the effectiveness of the spin injection process and low transversal ISHE voltage signals are detected. In addition, it is found that larger voltage signals are detected for the lowest SIO layer thickness highlighting the role of the spin diffusion length (λsd)/SIO layer thickness ratio. The values of ISHE voltage are rather low but allow us to determine the spin Hall angle of SIO (θSH ≈ 1.12% at T = 250 K), which is remarkably similar to that obtained for the well-known Py/Pt system, therefore suggesting that SIO could be a promising spin-Hall material.

Spin Hall magnetoresistance across a paramagnetic Pt/NdGaO3 interface

In recent years, spin Hall magnetoresistance (SMR) has emerged as an efficient way to probe the spontaneous magnetization state in ordered magnetic systems by electrical current. Less known is its versatility as a probe of materials that do not possess spontaneous magnetization, such as in paramagnets. In this work, SMR is used to probe paramagnetic NdGaO3 (NGO), a rare earth oxide, possessing a sizable spin–orbit interaction (L = 6). NGO has not been investigated earlier for its efficiency in propagating spins. We have performed extensive temperature and angle dependent-magnetoresistance (ADMR) studies along different crystallographic axes in NGO, using platinum (Pt) as a spin injector and a detector and utilizing (inverse) spin Hall effect. We find a close correlation between the temperature dependence of the ADMR response with magnetization in NGO and a linear current bias dependence of the ADMR amplitudes. These are characteristics of the SMR effect in Pt/NGO, arising from the torque acting on localized moments in NGO and considering crystal field induced intermultiplet transitions with temperature. Control experiments on Pt/SrTiO3 and Pt/SiO2 devices were also carried out in order to validate the observed SMR response in the Pt/NGO bilayer and to rule out magnetoresistive contributions from Pt.

Pump wavelength-dependent terahertz spin-to-charge conversion in CoFeB/MgO Rashba interface

Spin/charge interconversion mechanisms provide an essential handle to generate and detect spin currents. Their applications at different timescales are critical in spintronics since they cover a technologically relevant broadband spectrum. While the inverse spin Hall effect is known to be robust from quasi-static to sub-picosecond timescales, the conversion efficiency evolution of the inverse Edelstein effect has not been addressed yet. In this work, we report that while the quasi-static response of the inverse Edelstein effect can be comparable to that of the most efficient inverse spin Hall systems, a drastic drop of efficiency is observed in the terahertz (THz) regime. This behavior at the sub-picosecond timescale is qualitatively understood from the dependence of the inverse Edelstein effect on the energy distribution of spin-carrier entities, which is different between thermalized carriers in the quasi-static regime and hot carriers generated by light pulses. This finding is supported by the pump-laser wavelength dependence in the THz regime for the inverse Edelstein effect, which offers a promising route for tunability of spintronic devices.

Electrical detection of spin pumping in van der Waals ferromagnetic Cr2Ge2Te6 with low magnetic damping

The discovery of magnetic order in atomically-thin van der Waals materials has strengthened the alliance between spintronics and two-dimensional materials. An important use of magnetic two-dimensional materials in spintronic devices, which has not yet been demonstrated, would be for coherent spin injection via the spin-pumping effect. Here, we report spin pumping from Cr2Ge2Te6 into Pt or W and detection of the spin current by inverse spin Hall effect. The magnetization dynamics of the hybrid Cr2Ge2Te6/Pt system are measured, and a magnetic damping constant of ~ 4–10 × 10−4 is obtained for thick Cr2Ge2Te6 flakes, a record low for ferromagnetic van der Waals materials. Moreover, a high interface spin transmission efficiency (a spin mixing conductance of 2.4 × 1019/m2) is directly extracted, which is instrumental in delivering spin-related quantities such as spin angular momentum and spin-orbit torque across an interface of the van der Waals system. The low magnetic damping that promotes efficient spin current generation together with high interfacial spin transmission efficiency suggests promising applications for integrating Cr2Ge2Te6 into low-temperature two-dimensional spintronic devices as the source of coherent spin or magnon current.

Crystal orientation dependent spin pumping in a Bi0.1Y2.9Fe5O12/Pt interface

Ferromagnetic resonance (FMR) based spin pumping is a versatile tool to quantify the spin-mixing conductance and spin-to-charge conversion (S2CC) efficiency of ferromagnet–normal metal (FM/NM) heterostructures. The spin-mixing conductance at the FM–NM interface can also be tuned by the crystal orientation symmetry of epitaxial FM. In this work, we study the S2CC in epitaxial bismuth-substituted yttrium iron garnet (Bi0.1Y2.9Fe5O12) thin-film Bi–YIG (100 nm) interfaced with heavy metal platinum (Pt, 8 nm) deposited by pulsed laser deposition on different crystal orientations of Gd3Ga5O12 substrates, i.e. [100] and [111]. The crystal structure and surface roughness characterized by x-ray diffraction and atomic force microscopy measurements establish epitaxial Bi–YIG [100] and Bi–YIG [111] orientations, and atomically flat surfaces, respectively. The S2CC quantification was realized using two complementary techniques, namely (i) FMR-based spin pumping and the inverse spin Hall effect (ISHE) at GHz frequencies and (ii) temperature-dependent spin Seebeck measurements. The FMR-ISHE results demonstrate that the [111]-oriented Bi–YIG/Pt sample shows significantly higher values of spin mixing conductance ((2.31 ± 0.23) × 1018 m−2) and spin Hall angle (0.01 ± 0.001) as compared to the [100]-oriented Bi–YIG/Pt. Longitudinal spin Seebeck measurements reveal that the [111]-oriented sample has a higher spin Seebeck coefficient (106.40 ± 10 nV mm−1 K−1). The anisotropic nature of the spin-mixing conductance and spin Seebeck coefficient in the [111] and [100] orientations are discussed using the magnetic environment elongation along the surface normal or parallel to the growth direction. Our results aid in understanding the role of crystal orientation symmetry in S2CC-based spintronics devices.

Optimizing spin pumping and spin mixing conductance via Cu spacer layer in Mn2Au/Py system

Switching magnetization with spin current via spin orbital torque is a novel approach towards energy-efficient spintronics. In this regard, high spin–orbit coupling materials such as heavy metals are required to create the spin current via spin Hall effect. In recent times, a lot of attention has been paid to replace heavy metals by antiferromagnets to be considered as a spin sink. The bimetallic antiferromagnet, Mn2Au has attracted interest due to its high Néel temperature (T N > 1000 K) and high spin Hall angle. Here, we present results from experiments on spin pumping and the inverse spin Hall effect (ISHE) employing ferromagnetic resonance in Mn2Au/Py and Mn2Au/Cu/Py systems. The values of Gilbert damping constant decrease while inverse spin Hall voltage increases with the insertion of Cu spacer layer. This unusual behaviour indicates that the interface plays an important role for tuning the spintronic parameters. The maximum effective spin mixing conductance () has been evaluated to be 36.20 × 1018 m−2.

Polarization transport in optical fibers beyond Rytov's law

We consider the propagation of light in arbitrarily curved step-index optical fibers. Using a multiple-scales approximation scheme, set-up in Fermi normal coordinates, the full vectorial Maxwell equations are solved in a perturbative manner. At leading order, this provides a rigorous derivation of Rytov's law. At next order, we obtain non-trivial dynamics of the electromagnetic field, characterized by two coupling constants, the phase and the polarization curvature moments, which describe the curvature response of the light's phase and its polarization vector, respectively. The latter can be viewed as an inverse spin Hall effect of light, where the direction of propagation is constrained along the optical fiber and the polarization evolves in a frequency-dependent way.

Inverse orbital Hall effect and orbitronic terahertz emission observed in the materials with weak spin-orbit coupling

The Orbital Hall effect, which originates from materials with weak spin-orbit coupling, has attracted considerable interest for spin-orbitronic applications. Here, we demonstrate the inverse effect of the orbital Hall effect and observe orbitronic terahertz emission in the Ti and Mn materials. Through spin-orbit transition in the ferromagnetic layer, the generated orbital current can be converted to charge current in the Ti and Mn layers via the inverse orbital Hall effect. Furthermore, the inserted W layer provides an additional conversion of the orbital-charge current in the Ti and Mn layers, significantly enhancing the orbitronic terahertz emission. Moreover, the orbitronic terahertz emission can be manipulated by cooperating with the inverse orbital Hall effect and the inverse spin Hall effect in the different sample configurations. Our results not only discover the physical mechanism of condensed matter physics but also pave the way for designing promising spin-orbitronic devices and terahertz emitters.

Anisotropy of magnetic damping in Ta/CoFeB/MgO heterostructures

Magnetic damping controls the performance and operational speed of many spintronics devices. Being a tensor quantity, the damping in magnetic thin films often shows anisotropic behavior with the magnetization orientation. Here, we have studied the anisotropy of damping in Ta/CoFeB/MgO heterostructures, deposited on thermally oxidized Si substrates, as a function of the orientation of magnetization. By performing ferromagnetic resonance (FMR) measurements based on spin pumping and inverse spin Hall effect (ISHE), we extract the damping parameter in those films and find that the anisotropy of damping contains four-fold and two-fold anisotropy terms. We infer that four-fold anisotropy originates from two-magnon scattering (TMS). By studying reference Ta/CoFeB/MgO films, deposited on LiNbO3 substrates, we find that the two-fold anisotropy is correlated with in-plane magnetic anisotropy (IMA) of the films, suggesting its origin as the anisotropy in bulk spin–orbit coupling (SOC) of CoFeB film. We conclude that when IMA is very small, it’s correlation with two-fold anisotropy cannot be experimentally identified. However, as IMA increases, it starts to show a correlation with two-fold anisotropy in damping. These results will be beneficial for designing future spintronics devices.

Inverse Altermagnetic Spin Splitting Effect‐Induced Terahertz Emission in RuO2

AbstractThe relativistic inverse spin Hall effect (ISHE) plays a pivotal role in terahertz (THz) emission in magnet/heavy metal bilayers. Here, THz emission from RuO2/Py bilayers is reported due to not only the relativistic ISHE but also the nonrelativistic inverse altermagnetic spin splitting effect (IASSE) in RuO2. For the (100)‐oriented RuO2/Py bilayers, the THz emission is greatly enhanced owing to IASSE once the polarization direction of the spin current (from the Py layer induced by pump laser) is parallel to the Néel vector of RuO2, producing the anisotropic THz emission with twofold symmetry. In contrast, the RuO2(110)/Py bilayer only exhibits isotropic THz emission because of the absence of IASSE‐induced spin‐charge conversion in the (110)‐oriented RuO2 films. Apart from the fundamental significance of exploring the IASSE‐induced spin‐to‐charge conversion, the finding also enriches the physical mechanism and modulation method of THz emission in spintronic systems.

Efficient Spin-to-Charge Conversion via Altermagnetic Spin Splitting Effect in Antiferromagnet RuO_{2}.

The relativistic spin Hall effect and inverse spin Hall effect enable the efficient generation and detection of spin current. Recently, a nonrelativistic altermagnetic spin splitting effect (ASSE) has been theoretically and experimentally reported to generate time-reversal-odd spin current with controllable spin polarization in antiferromagnet RuO_{2}. The inverse effect, electrical detection of spin current via ASSE, still remains elusive. Here we show the spin-to-charge conversion stemming from ASSE in RuO_{2} by the spin Seebeck effect measurements. Unconventionally, the spin Seebeck voltage can be detected even when the injected spin current is polarized along the directions of either the voltage channel or the thermal gradient, indicating the successful conversion of x- and z-spin polarizations into the charge current. The crystal axes-dependent conversion efficiency further demonstrates that the nontrivial spin-to-charge conversion in RuO_{2} is ascribed to ASSE, which is distinct from the magnetic or antiferromagnetic inverse spin Hall effects. Our finding not only advances the emerging research landscape of altermagnetism, but also provides a promising pathway for the spin detection.