Inverse Spin Hall Effect Voltage Research Articles

Microwave spin-pumping from an antiferromagnet FeBO3

Canted antiferromagnets offer great potential in fundamental research and for use in applications due to their unique properties. The presence of the Dzyaloshinskii–Moriya interaction (DMI) leads to the existence of a weak ferromagnetic moment at room temperature. We study both theoretically and experimentally microwave spin pumping by a quasi-ferromagnetic mode from a canted easy plane antiferromagnet with weak ferromagnetism FeBO3. The conversion of a microwave signal into a constant voltage is realized using the inverse spin Hall effect in an iron borate/heavy metal heterostructure. We use an additional bias magnetic field to selectively tune the resonance frequency of such a microwave detector over a wide range up to 43.5 GHz with a potential sensitivity near 2.5 µV W−1. We confirm the pure spin current nature by changing the polarity of the detected via inverse spin Hall effect voltage by switching the direction of the bias magnetic field. We believe that our results will be useful for the development of highly tunable, portable and sensitive microwave antiferromagnet-based functional devices.

Pure Spin Transport in YIG Films with Amorphous‐to‐Crystalline Transformation

AbstractMagnetic insulators, especially Y3Fe5O12 (YIG), are considered promising candidates for spin‐based device applications due to their ultralow damping, high spin injection efficiency, and long‐distance spin propagation. However, these intriguing features are widely studied based on crystallization YIG films. Pure spin phenomena, like spin transport in YIG films with structural evolution, remain unclear. Herein, pure spin transportation is systematically investigated in the sandwich structure formed by YIG, the inserted layer‐nominal YIG (n‐YIG) with a varied crystalline structure and heavy metal Platinum (Pt). By applying ferromagnetic resonance (FMR)‐driven inverse spin Hall effect (ISHE) measurement, the detected ISHE voltage signal presented a strong correlation with the thickness of n‐YIG and its crystalline phase. A significant increasement in spin transportation is obtained for the crystallized n‐YIG via a high‐temperature annealing. These results demonstrate that pure spin current is transported availably in the structural evolution of YIG films. Furthermore, the element‐specific X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD) spectra on the n‐YIG films showed a distinction for the crystallized n‐YIG which indicates that the spin propagation is correlated to its magnetic order. These findings are instructive for low‐dissipation spin‐based 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.

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.

Reproducible low Gilbert damping yttrium iron garnet by magnetron sputtering

Reproducible growth of single-crystalline (111) yttrium iron garnet (YIG) with very low Gilbert damping (α) has been reported by the use of several techniques, and continues to attract the attention of many groups in sprintronics and magnonics. We report on the growth of YIG thin films onto GGG (111) substrates by magnetron sputtering, followed by an ex-situ oxygen flow heat treatment. The magnetic properties were studied by ferromagnetic resonance, and the structural and morphological properties by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. The annealing parameters and thickness dependency on the magnetic properties was systematically investigated. A decrease in α for almost ten times was found preventing the YIG growth at the edges of the substrate by the use of lithography. For YIG 60 nm thick α were measured as (1.72 ± 0.08) × 10−4, Ms = 179 ± 2 emu cm−3, and surface roughness as 0.23 nm. To quantify the growth as being of good quality, we measured the spin current injection via spin pumping to an adjacent bismuth-doped copper layer with spin mixing conductance g↑↓ = 2.16 × 1018 m−2, for a platinum layer g↑↓ = 2.17 × 1018 m−2, with the detection of a 7 μV in the inverse spin Hall effect voltage, quantities which are in good agreement with the best values reported so far.

Large Spin Pumping and Inverse Spin Hall Effect in Ta/Py Bilayer Structures

Spin mixing conductance at the ferromagnet (FM)/heavy metal (HM) interface is a key parameter to estimate the spin current injection into heavy metal. The electrical detection of such injected spin current in heavy metal is possible via inverse spin Hall effect (ISHE). Herein, a large spin mixing conductance in the range of (4.956.52) 1018 m−2 in Ta/permalloy(Py) bilayer structures is reported. In‐plane angular‐dependent ISHE voltage measurements in Ta/Py samples reveal the dominance of spin pumping voltage component over the other spin rectification contributions. Voltage contribution due to spin pumping and anisotropic magnetoresistance (AMR) increases with the Py thickness due to the enhancement in spin pumping and increase in spin‐dependent scattering, respectively. Anomalous Hall effect (AHE) contribution in Py is found to be relatively small.

Interface-driven spin pumping and inverse Rashba-Edelstein effect in FeGaB/Ag/BiSb multilayers

Spin-orbit-coupling (SOC) plays a critical role in spin-to-charge conversion (SCC) mechanism. The SCC process is usually investigated by injecting a spin current from ferromagnet (FM) into a large SOC normal metal (SOC-NM) and then measuring the voltage generated by inverse spin Hall effect (ISHE). Recently, a new mechanism of SCC at inversion symmetry breaking interfaces between topological insulators (TIs) and magnetically ordered materials has been introduced, which is driven by the inverse Rashba-Edelstein effect (IREE). Motivated by this result, we have investigated the IREE effect of a simple binary three-dimensional TI Bi85Sb15 (BiSb). The model system used here is a trilayer of FeGaB/Ag/BiSb with different Ag thickness made insitu with a combination of dc magnetron sputtering and pulsed laser ablation. The SCC efficiency has been evaluated by measuring ferromagnetic resonance (FMR) driven ISHE voltage and extraction of the Gilbert damping (α) and interfacial spin mixing conductance (g↑↓) from the FMR line shape analysis. It is interesting to note that the charge current (Ic) increases with Ag thickness. This observation indicated that the IREE process at the Ag/BiSb interface dominates over ISHE in the bulk of BiSb film. The conversion efficiency of IREE is determined by calculating the IREE length (λIREE), which increases with the thickness of the Ag layer. These findings offer a method to generate and detect the IREE in a room temperature deposited heterostructure using simple coplanar waveguide setup.

Inverse spin Hall voltage enhancement in cascaded Py/Ta micro-array

Microwave power harvesting is one of the promising ways to solve energy problems in the future. Improving the power harvesting ability is the central work in this area. The inverse spin Hall effect (ISHE) in ferromagnetic (FM) and nonmagnetic (NM) metallic bilayers can be utilized to convert microwave power to direct current, which may be one of the candidates of microwave power harvesting. In this work, a FM/NM microstrip array is proposed to enhance the ISHE signal, while the spin rectification effect signal in the FM layer is suppressed. This enhancement is equivalent to connecting the power sources in series, namely, the ISHE voltage is proportional to the number of the FM/NM microstrips. Our work fertilizes the spintronics and shows the possibility to use ISHE in microwave power transfer and harvesting.

Magnetization Reversal and Dynamics in Epitaxial Fe/Pt Spintronic Bilayers Stimulated by Interfacial Fe3O4 Nanoparticles.

We have explored the impact of elevated growth and annealing temperatures on the local interfacial structure of thin Fe(12 nm)/Pt(10 nm) spintronic bilayers, epitaxially grown on MgO (100), and their correlation to magnetization reversal and dynamics. Electron-beam evaporation growth and subsequent annealing at 450 °C causes significant roughening of the MgO/Fe interface with irregular steps and multilevel (100) MgO surface terraces. Consequently, threading dislocations emerging at the step edges propagated in the Fe layer and terminated at the Fe/Pt interface, which appears pitted with pits 1.5–3 nm deep on the Fe side. Most of the pits are filled with the overlying Pt, whereby others by ferrimagnetic Fe3O4, forming nanoparticles that occupy nearly 9% of the Fe/Pt interfacial area. Fe3O4 nanoparticles occur at the termination sites of threading dislocations at the Fe/Pt interface, and their population density is equivalent to the density of threading dislocations in the Fe layer. The morphology of the Fe/Fe3O4/Pt system has a strong impact on the magnetization reversal, enhancing the coercive field and inducing an exchange bias below 200 K. Furthermore, low-temperature spin pumping and inverse spin Hall effect voltage measurements reveal that below their blocking temperature the nanoparticles can influence the spin current transmission and the spin rectification effects.

Optimization of YIG/Bi stacks for spin-to-charge conversion and influence of aging

We show that an optimized growth of magnetic layer/non-magnetic layer stacks allows for the improvement of the spin-to-charge conversion efficiency. From the analysis of the voltage signal generated in spin pumping experiments due to the inverse spin Hall effect (ISHE) on Y3Fe5O12 (YIG)/Bi stacks, we have determined values for the spin Hall angle and the spin-diffusion length in Bi of 0.0068(8) and 17.8(9) nm, respectively. Based on these results, we have also studied the influence of aging on the spin-to-charge conversion efficiency by performing spin pumping experiments on YIG/Bi stacks after exposing the samples to ambient conditions for several days and up to 150 days. We have found that in YIG/Bi samples with Bi thicknesses around or below the spin-diffusion length, the ISHE voltage signal is still above 80% of its initial value after 100 days.

Spin Pumping and Inverse Spin Hall Effect in Iridium Oxide

AbstractLarge spin‐to‐charge conversion (spin Hall angle) and spin Hall conductivity are prerequisites for development of next generation power efficient spintronic devices. In this context, heavy metals (e.g., Pt, W, etc.), topological insulators, and antiferromagnets are usually considered because they exhibit high spin–orbit coupling (SOC). In addition to the above materials, 5d transition metal oxide, for example, iridium oxide (IrO2) is a potential candidate which exhibits high SOC strength. Here a study of spin pumping and inverse spin Hall effect (ISHE), via ferromagnetic resonance (FMR), in IrO2/CoFeB system is reported. By investigating the in‐plane angular dependence of the ISHE voltage, the individual contribution of spin pumping and other spin rectification effects in the magnetic layer is identified. The authors' analysis shows significant contribution of spin pumping effect to the ISHE signal. It is shown that polycrystalline IrO2 thin film exhibits high spin Hall conductivity and spin Hall angle which are comparable to the values of Pt.

Spin wave interference detection via inverse spin Hall effect

In this Letter, we present experimental data that demonstrate a spin wave interference detection using an inverse spin Hall effect (ISHE). Two coherent spin waves are excited in a yttrium-iron garnet waveguide by continuous microwave signals. The initial phase difference between the spin waves is controlled by the external phase shifter. The ISHE voltage is detected at a distance of 2 and 4 mm away from the spin wave generating antennas by an attached Pt layer. Experimental data show ISHE voltage oscillation as a function of the phase difference between the two interfering spin waves. This experiment demonstrates an intriguing possibility of using ISHE in a spin wave logic circuit converting a spin wave phase into an electric signal.

High spin pumping efficiency in Fe80Co20/Ta bilayers

We have investigated the spin pumping phenomenon in Fe80Co20/Ta bilayers of different thicknesses in which the ferromagnet grows epitaxially on MgO substrates. We have obtained a Gilbert damping constant for Fe80Co20 as low as α = 1.3(1) × 10−3, which is smaller than values generally reported in metallic ferromagnets. From the dependence of α with the Fe80Co20 thickness, we extracted the value of the effective spin mixing conductance = 5.7(3) × 1014 cm−2. Analyzing the Ta and Fe80Co20 thickness dependence of the inverse spin Hall effect voltage, we obtained the transport parameters = 1.1(3) nm and = –0.024(3). We have developed an expression to quantify the efficiency of the spin pumping phenomenon in ferromagnetic/nonmagnetic metal bilayers. The calculated efficiency shows that the Fe80Co20/Ta system is up to an order of magnitude more efficient than other metallic ferromagnetic bilayers reported in the literature.

Acoustic wave surfing: spin waves and spin pumping driven by elastic wave

In magnon spintronics it is fundamental that magnons can propagate over large distances to allow spin flux or information to be processed. Through micromagnetic simulations we investigate the spin-wave propagation driven by acoustic excitation in narrow Ni stripes, varying the level of coupling between spin and acoustic waves. We consider different cases depending on the extension of the acoustic wave propagation, which is generated on the left end of the stripe. When acoustic waves are confined at the origin, the spin waves are free to propagate but vanish after the decay length, which is dependent on the dissipation. On the other hand, when the acoustic waves are present in the whole stripe, spin and acoustic waves propagate together with the spin wave maintaining a constant amplitude. Images of the spin-wave propagation modes and the dispersion relations are discussed for different acoustic wave attenuation lengths. Motivated by recent experiments, we consider a Pt line over and crossing the Ni stripe and calculate the spin and charge current maps at the Ni/Pt interface and the Pt line, respectively, and the AC and DC components of the inverse spin Hall effect voltage.

Electrically tunable inverse spin Hall effect in SrIrO3/Pb(Mg1/3Nb2/3)0.7 Ti0.3O3 heterostructures through interface strain coupling

Oxide spin detector materials are highly desired for emergent all-oxide spintronics. In this work, Permalloy/SrIrO3/Pb(Mg1/3Nb2/3)0.7 Ti0.3O3 (Py/SIO/PMNPT) heterostructures were prepared by pulsed laser deposition of SIO thin films epitaxially on (001)-oriented single crystalline PMNPT substrates, followed by sputter deposition of Py films upon SIO through a shadow mask. The paramagnetic SIO layer, with a large spin–orbit coupling, serves as a detector to check the spin current pumped from the adjacent ferromagnetic Py layer through the inverse spin Hall effect (ISHE). It is observed that the spin pumping amplitude can be reversibly tuned by about 50% through applying a 10 kV/cm electric field on the piezoelectric PMNPT substrate. The ISHE voltage shows a butterfly hysteresis resembling the strain-field curve of PMNPT, indicating the relevance of strain coupling at the SIO/PMNPT interface. In situ x-ray diffraction reveals that both in-plane and out-of-plane lattice parameters of SIO vary with the field applied on PMNPT. These results highlight that SIO is a promising candidate material for spin detection, and the efficiency of spin to charge conversion in SIO can be tuned electrically in SIO/PMNPT heterostructures.

Manipulation of the inverse spin Hall effect in palladium by absorption of hydrogen gas

The spintronic properties of a palladium thin film have been investigated in the presence of hydrogen gas in cobalt/palladium bilayers. Measurements of the inverse spin Hall Effect (ISHE) using cavity ferromagnetic resonance allow estimations of the spin Hall conductivity and spin diffusion length in both nitrogen and hydrogen gas atmospheres. Unwanted spin rectification effects are removed using a simple method of inverting the spin current direction with respect to the measurement setup. Absorption of hydrogen gas in the Pd layer at just 3% concentration results in a reduced ISHE voltage amplitude and bilayer resistance. Fitting the ISHE voltage against the Pd layer thickness demonstrates that the spin diffusion length decreases by 23% in the presence of a hydrogen gas. On the other hand, the results indicate that there is no significant change in the spin Hall conductivity of Pd due to hydrogen absorption.

Nonlocal Detection of Out-of-Plane Magnetization in a Magnetic Insulator by Thermal Spin Drag.

We demonstrate a conceptually new mechanism to generate an in-plane spin current with out-of-plane polarization in a nonmagnetic metal, detected by nonlocal thermoelectric voltage measurement. We generate out-of-plane (∇T_{OP}) and in-plane (∇T_{IP}) temperature gradients, simultaneously, acting on a magnetic insulator-Pt bilayer. When the magnetization has a component oriented perpendicular to the plane, ∇T_{OP} drives a spin current into Pt with out-of-plane polarization due to the spin Seebeck effect. ∇T_{IP} then drags the resulting spin-polarized electrons in Pt parallel to the plane against the gradient direction. This finally produces an inverse spin Hall effect voltage in Pt, transverse to ∇T_{IP} and proportional to the out-of-plane component of the magnetization. This simple method enables the detection of the perpendicular magnetization component in a magnetic insulator in a nonlocal geometry.

High temperature spin cluster glass behavior in Co- and Si-substituted garnet ferrite thin films

In this study, lutetium iron garnet (Lu3Fe5O12; LuIG) thin films have been grown on Y3Al5O12 (1 1 1) substrates by a pulsed laser deposition and are co-substituted with strong magnetically anisotropic ions of Co2+ and nonmagnetic ones of Si4+. LuIG is a garnet-structured ferrimagnet with an exceptionally low Gilbert damping constant as 10−5. The substitution of Co2+ and Si4+ induces a chemical disorder and competing antiferromagnetic and ferromagnetic interactions, which induce a spin glass behavior. When the Co–Si substitution ratio is increased, a spin-freezing behavior is observed below the spin-freezing temperature TG = 190–220 K of the Lu3Fe4Co0.5Si0.5O12 film; this indicates the presence of a cluster glass phase. The film demonstrates a characteristic memory effects in the temperature range 120–180 K, which are below TG; this reveals the presence of a metastable magnetic state in the multi-valley energy landscape with shallow activation energy barriers. Ferromagnetic resonance measurements confirm increased perpendicular anisotropy energy induced by Co substitution and spin-wave characteristics including the inverse spin Hall effect voltage (VISHE). Lu3Fe5-2xCoxSixO12 films show an increase in damping and a decrease in VISHE at the cryogenic temperature, which are attributed to the impurity relaxation mechanism. Therefore, the Co- and Si-substituted films exhibit strong spin-wave damping at a low temperature, which reflects the spin-freezing dynamics of cluster glass behaviors.

Yttrium Iron Garnet Thickness Influence on the Spin Pumping in the Bulk Acoustic Wave Resonator

The features of phonon–magnon interconversion in acoustic resonator determine the efficiency of spin pumping from YIG into Pt that may be detected electrically through the inverse spin Hall effect (ISHE). Based on the methods developed in previous works for calculating resonator structures with a piezoelectric (ZnO) and a magnetoelastic layer in contact with the heavy metal (YIG/Pt), we present the results of numerical calculations of YIG film thickness influence on acoustically driven spin waves. We obtain some YIG film thickness regions with various behavior of dc ISHE voltage UISHE. At micron and submicron thicknesses, the higher spin wave resonance (SWR) modes (both even and odd) can be generated with efficiency comparable and even exceeding that of the main mode. The absolute maximum of UISHE is achieved at the thickness about s1 ≈ 208 nm under the excitation of the first SWR.