Inverse Spin Hall Effect Research Articles

Simultaneous Terahertz Pulse Generation and Manipulation with Spintronic Coding Surface

AbstractThe utilization of spintronic terahertz (THz) emitters has a significant influence on broadband coherent spectroscopy and imaging at THz frequencies. By using femtosecond light to irradiate the spintronic heterostructures, spin currents from the ultrafast demagnetization effect can be transformed into charge currents through the inverse spin Hall effect, leading to the emission of THz waves. In this work, through the incorporation of sequential and inverse deposition of W‐Co20Fe60B20‐Pt heterostructure films, control is gained over the spin currents and THz waveforms, enabling it to achieve a 180° phase difference across a broad frequency spectrum while efficiently radiating THz waves. This, in turn, allows it to control the spatial phase of THz radiation. To test the device's capabilities, lithography‐based devices capable of focusing, producing vortexes, and dividing beams are manufactured. This investigation aims to advance the development of THz pulse sources while providing essential support for cutting‐edge technologies such as THz spectroscopy, high‐resolution imaging, and high‐speed communications.

Spin–Charge Conversion in Hybrid Structure PbZrO3/Y3Fe5O12/Pt

Multifunctional oxide heterostructures exhibiting magnetoelectric properties show great potential in advanced applications which are attracting a number of recent investigations. Herein, hybrid structures are presented including the antiferroelectricity film PbZrO3 (PZO) and the ferrimagnetic insulator (FMI) yttrium iron garnet (Y3Fe5O12, (YIG)) film by means of pulse laser deposition and magnetron sputtering, respectively. A visible double ferroelectricity hysteresis loop for PZO at low electrical field and the distinct X‐ray magnetic circular dichroism (XMCD) spectra for YIG are obtained. To study the spin current transfer processes between platinum (Pt) and the PZO/YIG system, the Pt film is deposited on the PZO/YIG bilayers as the conversion detector and the spin–charge conversion voltage can be obtained via inverse spin Hall effect (ISHE) under thermal gradient excitation. These results indicate that the hybrid structure PZO/YIG/Pt provides a potential route to realize an electric field control of spin–charge conversion and is instructive for future low‐power multiferroic heterostructures‐based spintronic devices.

Terahertz spin-to-charge conversion in ferromagnetic Ni nanofilms

Abstract Spintronic terahertz (THz) emission via spin-to-charge conversion (SCC) has been widely studied in ferromagnets (FM)/nonmagnets (NM) structures, in which various mechanisms of SCC have been confirmed in different NM materials. However, it is rare to find a material having multiple SCC mechanisms at the same time. Here, we report a ferromagnetic metal Ni film with diverse functions in the SCC process, by performing THz emission experiments in single Ni layer, FM/Ni, Ni/NM bilayers and FM/Ni/NM trilayers. It is demonstrated that in Ni monolayer, THz emission is radiated by the anomalous Hall effect and ultrafast demagnetization of Ni film. In FM/Ni, the Ni film acts as an SCC implementer and THz emission is mainly generated by the inverse spin Hall effect (ISHE) of Ni. In Ni/NM, the Ni film acts as a spin injector and provides spin currents to be converted to charge current via ISHE of heavy metal NM, inducing THz emission. In FM/Ni/NM, THz emission mainly comes from ISHE of FM/Ni, Ni/NM, and FM/NM, and their domination is relative to Ni thickness. Our findings show a ferromagnetic film not only acts as a spin injector but also as an SCC implementer, providing a new concept to design spintronic THz emitters.

Proposal for a spin logic device based on magneto‐electric effect and spin Hall effect

AbstractBased on magneto‐electric (ME) effect and spin Hall effect (SHE), the authors propose a novel spin logic device named MESH‐SLD. In MESH‐SLD, the charge current is transmitted in the channel by employing inverse SHE, which solves the dissipation problem of spin current in the channel of all‐spin logic device (ASLD). By using a magnetization‐dynamics/spin‐transport hybrid model, the authors have investigated the influence of working voltage, channel lengths, and materials on the performance of the MESH‐SLD. And the simulation results show that the energy dissipation of the MESH‐SLD only increases approximately linearly with the increase of channel length, while the switching delay remains almost unchanged. In addition, with the increase of the spin Hall angle of the channel material, the energy dissipation and the minimum working voltage of the MESH‐SLD decrease significantly. Most importantly, compared with conventional ASLD, the proposed MESH‐SLD improve the switching delay and the energy dissipation by about 2.5 times and 851.8 times, respectively.

Spin-wave cochlea and nonlocal magnetic resonance in a magnet

Spatial dependence of magnetization dynamics in a ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ film exposed to a magnetic-field gradient has been investigated by measuring local spin pumping and inverse spin-Hall effects. The result shows that, when microwaves are irradiated locally, magnetization precession is excited at a far distant position from the microwave irradiation position. By measuring the field and microwave frequency dependence, we found that the observed magnetization dynamics is attributed to nonlocal resonance of magnetization as well as the spatial change in the spin-wave dispersion under the magnetic-field gradient, which can be applied to realizing an innate microwave spectrometer: a spin-wave cochlea.

Dependence of the Inverse Spin Hall Voltage in Py/Ta Microstrip Array on the Microstrip Width

Since inverse spin Hall effect (ISHE) can transform microwave energy into direct current (DC) energy in ferromagnetic (FM)/nonmagnetic (NM) bilayer metal materials, the ISHE-based FM/NM microstrip arrays have clear potential to be used for microwave power transmission and harvesting. Driven by the need for the miniaturization of electronic devices, it is essential to study the dependence of the characteristics of FM/NM microstrip arrays on their geometries. In this work, we have experimentally demonstrated that the Py/Ta microstrip array’s ISHE signal increases linearly with an increase in the Py/Ta microstrip width and that the effective saturation magnetization of the Py film shows the same change tendency. Moreover, the anisotropy field of the Py film increases linearly as the width decreases. Our work provides a valuable reference for the future miniaturization of ISHE-based rectifier devices.

Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin–phonon interactions

Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modeling, two excitation processes of spin dynamics in NiO: an off-resonant instantaneous optical spin torque in (111) oriented films and a strain-wave-induced THz torque induced by ultrafast Pt excitation in (001) oriented films. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be < 50 fs and > 300 fs, respectively, and thus open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.

Spin-charge-coupled transverse resistance in an ambipolar conductor YH2-based Hall-bar structure with perpendicularly magnetized current-injection electrodes

Spin-charge (SC) coupling is crucial in spintronics and the coupling mechanisms can be classified into bulk characteristic via spin-orbit interaction (SOI) or the interfacial characteristic provided by a junction formed by magnetic and nonmagnetic conductors. The two types of SC couplings account for the transverse resistance (TR) in a planer channel subjected to out-of-plane-polarized spin current injection. This is because interfacial spin-accumulation induces the diffusive transport of spin-angular momentum, which is converted into transverse charge accumulation via SOI. We explore the SC coupling characteristics of a lateral junction consisting of (i) a rare-earth transition metal (RE-TM) ferrimagnet with perpendicular magnetic anisotropy and (ii) a compensated metal, YH2, where electrons and holes simultaneously participate in spin and charge transports. This set-up allows us to observe the TR, which mirrors the magnetization of the RE-TM employed as the current-source electrode in the planer Hall-bar structure. The results show that the inverse spin Hall effect contributes significantly to the TR. Along with the TR measurement, we formulate a minimal expression of the TR when out-of-plane-polarized electron and hole spin currents are injected from the magnetic electrode. Since this formulation is independent of the details of the SC coupling mechanism, it is applied to interpret the observation result to reveal the SC coupling characteristics of the RE-TM and YH2 set-up.

Spin Seebeck effect mediated reversal of vortex-Nernst effect in superconductor-ferromagnet bilayers

We report on the observation of sign reversal of vortex-Nernst effect in epitaxial NbN/Fe bilayers deposited on MgO (001) substrates. Strong coupling between vortex magnetisation and ferromagnetic magnetisation at the NbN/Fe bilayer interface is presented. In NbN/Fe bilayer thin films an apparent sign reversal of vortex-Nernst signal under a temperature gradient with magnetic field and temperature is observed when the thickness of Fe is increased up to 5 nm. This reversal of the vortex-Nernst effect is associated with the enhancement of the spin Seebeck effects (SSE) near Tc due to coherence peak effect (CPE) and strong coupling of vortex magnetisation and ferromagnetic magnetisation at the interface of the NbN/Fe bilayer. The observed large SSE via inverse spin Hall effect (ISHE) is due to the CPE below and close to TC, highlighting the high spin to charge conversion efficiency of NbN in this region. This work may contribute to the development of superconducting spintronic devices by engineering the coupling of the superconductor/ferromagnet interface.

Large Spin Hall Angle in Sputtered BiSb Topological Insulator on Top of Various Ferromagnets With In-Plane Magnetization for SOT Reader Application

A spin-orbit torque (SOT) reader using the inverse spin Hall effect was recently proposed as a candidate for magnetic recording beyond 4 Tbit/in2. However, SOT readers using conventional heavy metals have small output voltage and low signal-to-noise ratio (SNR) due to the small spin Hall angles of heavy metals. Demonstrated in this work is a large spin Hall angle of 2.6–5.1 in sputtered BiSb, a topological insulator, on top of various ferromagnets with in-plane magnetization. The spin Hall angle of BiSb is much larger than that of heavy metals, which is promising for SOT readers with large output and high SNR.

Scanning inverse spin Hall effect spectrometer by shorted coaxial probes.

In this work, a scanning inverse spin Hall effect measurement system based on a shorted coaxial resonator has been built, which provides a high throughput method to characterize spin transport properties. The system is capable of performing spin pumping measurements on patterned samples within an area of 100 × 100mm2. Its capability was demonstrated with Py/Ta bilayer stripes deposited on the same substrate with different thicknesses of Ta. The results show that the spin diffusion length is about 4.2nm with a conductivity of about 7.5 × 105Ω-1m-1, which leads to the conclusion that the intrinsic mechanism of spin relaxation of Ta is the Elliott-Yafet interactions. The spin Hall angle of Ta is estimated to be about -0.014 at room temperature. The setup developed in this work provides a convenient, efficient, and nondestructive way to obtain the spin and electron transportation characteristics of the spintronic materials, which will fertilize this community by developing new materials and figuring out their mechanism.

Spin to Charge Conversion in Semiconducting Antiferromagnetic Co3O4

Power efficient and faster spintronic devices require high spin current propagation efficiency from a ferromagnet (FM) to high spin orbit coupling material. Antiferromagnets (AFM) exhibiting high spin orbit coupling and faster spin dynamics have drawn great attention in such studies. Efficient spin current propagation in metallic AFMs via conduction electron showed promising results in spin to charge conversion physics. Recently, the insulating AFMs are also found to exhibit efficient spin current propagation due to the presence of magnonic modes. The semiconducting AFM Co3O4 is expected to show promising results in spin to charge conversion studies due to the simultaneous presence of magnon modes and conduction electrons. In this context, spin pumping and inverse spin Hall effect studies are carried out on a series of Co3O4(t nm)/Co(22 nm) samples where the t value varies from 0 to 26 nm. Damping analysis reveals that the spin diffusion length of Co3O4 is 2.5 ± 0.5 nm which is large in comparison to metallic AFMs. The maximum Hall angle of Co3O4 is found to be 0.26. A high spin transparency of 65.8% indicates efficient spin current propagation in the samples.

Hysteresis and training effect in the electric control of spin current in Pt/Y3Fe5O12 heterostructures

We have reported on the hysteresis and training effect of spin current in $\mathrm{Pt}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ heterostructures during subsequent cycles of ionic liquid gate voltage ${V}_{g}$. The inverse spin Hall effect voltage in spin pumping and spin Hall magnetoresistance exhibit diode-like behaviors in the first half cycle of ${V}_{g}$ and also show hysteresis in the first cycle of ${V}_{g}$. Both the diode-like behavior and the hysteresis become weak and even vanish in the second cycle of ${V}_{g}$ due to the training effect. The above experimental results can be well explained by the screening charge doping model, in which the charge and the local magnetic moment are asymmetrically distributed in the Pt layer. The applicability of this model is further confirmed by measurements of anisotropic magnetoresistance and ferromagnetic resonance. The diode-like behavior is attributed to interplay between the asymmetrically distributed local magnetic moment and the spin current relaxation in the Pt layer. The hysteresis and the training effect arise from the incompletely reversible process between oxidation and reduction of Pt atoms and the evolution of the surface morphology at the ionic liquid/Pt interface under electric gating. This work provides new insights to improve the functional performance of electrically controlled spin current devices.

Comparing spin injection in Fe75Co25/Bi2Te3 at GHz and optical excitations

Spin-to-charge conversion (S2CC) processes in thin-film heterostructures have attracted much attention in recent years. Here, we describe the S2CC in a 3D topological insulator Bi2Te3 interfaced with an epitaxial film of Fe75Co25. The quantification of spin-to-charge conversion is made with two complementary techniques: ferromagnetic resonance based inverse spin Hall effect (ISHE) at GHz frequencies and femtosecond light-pulse induced emission of terahertz (THz) radiation. The role of spin rectification due to extrinsic effects like anisotropic magnetoresistance (AMR) and planar Hall effects (PHE) is pronounced at the GHz timescale, whereas the THz measurements do not show any detectible signal, which could be attributed to AMR or PHE. This result may be due to (i) homodyne rectification at GHz, which is absent in THz measurements and (ii) laser-induced thermal spin current generation and magnetic dipole radiation in THz measurements, which is completely absent in GHz range. The converted charge current has been analyzed using the spin diffusion model for the ISHE. We note that regardless of the differences in timescales, the spin diffusion length in the two cases is comparable. Our results aid in understanding the role of spin pumping timescales in the generation of ISHE signals.

Room-temperature spin injection from a ferromagnetic semiconductor

Spin injection using ferromagnetic semiconductors at room temperature is a building block for the realization of spin-functional semiconductor devices. Nevertheless, this has been very challenging due to the lack of reliable room-temperature ferromagnetism in well-known group IV and III-V based semiconductors. Here, we demonstrate room-temperature spin injection by using spin pumping in a BiSb/(Ga,Fe)Sb heterostructure, where (Ga,Fe)Sb is a ferromagnetic semiconductor (FMS) with high Curie temperature (TC) and BiSb is a topological insulator (TI). Despite the very small magnetization of (Ga,Fe)Sb at room temperature (45 emu/cc), we detected spin injection from (Ga,Fe)Sb by utilizing the large inverse spin Hall effect (ISHE) in BiSb. Our study provides the first demonstration of spin injection at room temperature from a FMS.

Non-local architecture for spin current manipulation in silicon platforms

We have developed a non-local architecture for spin current injection, manipulation, and detection in n-doped bulk Si at room temperature. Spins are locally generated at the indirect gap of bulk Si by means of circularly polarized light and then detected by exploiting the inverse spin-Hall effect (ISHE) occurring inside a thin Pt pad deposited at the top of the Si substrate. We demonstrate that it is possible to modulate the transport properties of the optically injected spin current by applying a bias voltage along the direction of motion of the particles. In this case, we are able to explore both the spin diffusion regime, characterized by a spin diffusion length Ls ≈ 12 μm, and the spin drift regime with applied electric fields up to E = 35 V/cm. We demonstrate that the spin transport length of the electrons can be increased (or decreased) by more than 100% for electric fields antiparallel (or parallel) to the diffusion direction. As a consequence, the ISHE signal can be electrically controlled to have high or low output voltages from the non-local device.

Large inverse spin Hall effect in BiSb topological insulator for 4 Tb/in2 magnetic recording technology

It is technically challenging to shrink the size of a tunneling magnetoresistance reader to below 20 nm for magnetic recording technology beyond 4 Tb/in2 due to its complex film stack. Recently, we proposed a reader architecture based on the inverse spin Hall effect to resolve those challenges, referred below as spin–orbit torque (SOT) reader, whose structure consists of a SOT layer and a ferromagnetic layer. However, the heavy metal-based SOT reader has small output voltage and low signal-to-noise ratio (SNR) due to the limited spin Hall angle θSH (&amp;lt; 1) of heavy metals. In this Letter, we demonstrate the integration of BiSb topological insulator with strong inverse spin Hall effect into the SOT reader that can significantly improve the output voltage and SNR. First, we theoretically calculate the noises in a 20 × 20 nm2 BiSb-based SOT reader to establish the relationships between SNR and θSH at various bias currents. We then demonstrate proof-of-concept BiSb-based SOT readers using CoFe/MgO/BiSb stack, which show large output voltages up to 15 mV at an input current of 9.4 kA/cm2 at room temperature. We project a giant θSH = 61 for BiSb. Our work demonstrates the potential of BiSb for SOT reader beyond 4 Tb/in2 magnetic recording technology.

Sizable spin-to-charge conversion in PLD-grown amorphous (Mo, W)Te2−x films

We report on the spin-to-charge conversion (SCC) in Mo0.25W0.75Te2−x (MWT)/Y3Fe5O12 (YIG) heterostructures at room temperature. The centimeter-scale amorphous MWT films are deposited on liquid-phase-epitaxial YIG by pulsed laser deposition technique. The significant SCC voltage is measured in the MWT layer with a sizable spin Hall angle of ∼0.021 by spin pumping experiments. The control experiments by inserting MgO or Ag layer between MWT and YIG show that the SCC is mainly attributed to the inverse spin Hall effect rather than the thermal or interfacial Rashba effect. Our work provides a novel spin-source material for energy-efficient topological spintronic devices.

Terahertz Spectral Signatures of Ultrafast Spin Transports in Ferromagnetic Heusler Alloy

AbstractAlthough the Co‐based Heusler compounds are predicted to be half‐metals, their sub‐picosecond demagnetization dynamics upon laser excitation show a transition‐metal‐like behavior. Any possible role of ultrafast nonlocal spin transport on the ultrafast demagnetization of half‐metallic Heusler compounds has only been inferred indirectly by time‐resolved magneto‐optical Kerr effect. Here, an ultrafast optically driven spin current traveling from Co2FeSi half metal into an adjacent Pt layer by using terahertz (THz) emission time‐domain spectroscopy (TDS) is demonstrated. By varying the magnetic field and excitation symmetry, the sizable THz generation from Co2FeSi/Pt stack arises from optically induced spin transport across the Co2FeSi/Pt interface in conjunction with spin‐to‐charge current conversion, via the inverse spin Hall effect (ISHE). The chemical ordering, interface roughness and magnetization of the samples become vital to engineer the THz emission properties. The amplitude of THz emission is comparable to that of CoFeB/Pt stack, thereby indicating Co2FeSi as an efficient ultrafast light‐driven spin current injector. Finally, by varying the pumping energy, the contributions are distinguished to the ultrafast spin current from thermalization and optical excitation of majority spins in Heusler alloy. This work illustrates THz emission TDS as a powerful tool to investigate the ultrafast spintronic properties of Heusler alloy/normal‐metal bilayers.

Influence of parametric instability on spin pumping by dipole-exchange magnetostatic surface waves in YIG–Pt structures

The purpose of this work is to study the influence of four-magnon (4M) parametric instability on spin pumping by dipole-exchange magnetostatic surface waves (MSSW) with the help of the inverse spin Hall effect (ISHE) in structures based on yttrium-iron garnet (YIG) and platinum (Pt). Methods. The experiments were carried out using the delay line structures based on YIG(900 nm)/Pt(9 nm) where electromotive force (EMF) induced by ISHE demonstrates a growth at the frequencies of the resonant interaction between MSSW and volume exchange modes. The frequency dependencies of the amplitude and phase for the delay line structure and EMF (𝑈(𝑓)) from the platinum layer were studied as a function of the MSSW power. Results. It was shown that the resonant EMF growth at the frequencies of dipole-exchange resonances is caused by the presence of Van Hove singularities in the density of states for spin waves at such frequencies that leads to an increase in the efficiency of electron-magnon scattering at the YIG–Pt interface. A growth in MSSW power beyond the threshold of 4M instability development results in a “smoothing” of resonant particularities in the EMF frequency dependence 𝑈(𝑓) that can be explained by decreasing efficiency of spin pumping due to destruction of dipole-exchange resonances and related singularities in the density of states of spin waves. Conclusion. Obtained results may be of interest for the development of highly sensitive spin current detectors, as well as for the implementation of spintronic devices.