Spin Pumping Voltage Research Articles

Enhanced spin pumping in heterostructures of coupled ferrimagnetic garnets

Spin pumping has significant implications for spintronics, providing a mechanism to manipulate and transport spins for information processing. Understanding and harnessing spin currents through spin pumping is critical for the development of efficient spintronic devices. The use of a magnetic insulator with low damping enhances the signal-to-noise ratio in crucial experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping. A magnetic insulator coupled with a heavy metal or quantum material offers a more straightforward model system, especially when investigating spin-charge interconversion processes to greater accuracy. This simplicity arises from the absence of unwanted effects caused by conduction electrons unlike in ferromagnetic metals. Here, we investigate the spin pumping in coupled ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with heavy-metal (Pt) using the inverse spin Hall effect. It is observed that magnon transmission occurs at both of the FiMs FMR positions. The enhancement of spin pumping voltage (Vsp) in the FiM garnet heterostructures is observed. The plausible reason might be the interfacial exchange coupling between FiMs. The modulation of Vsp is achieved by tuning the bilayer structure. Further, the spin mixing conductance for these coupled systems is found to be ≈1018 m−2. Our findings describe a coupled FiM system for the investigation of magnon coupling providing opportunities for magnonic devices.

Enhancement of spin to charge conversion efficiency at the topological surface state by inserting normal metal spacer layer in the topological insulator based heterostructure

In this study, we report efficient spin to charge conversion (SCC) in the topological insulator (TI) based heterostructure (BiSbTe1.5Se1.5/Cu/Ni80Fe20) by using spin-pumping technique, where BiSbTe1.5Se1.5 is the TI and Ni80Fe20 is the ferromagnetic (FM) layer. The SCC, characterized by inverse Edelstein effect length (λIEE) in the TI material, gets altered with an intervening Copper (Cu) layer, and it depends on the interlayer thickness. The introduction of Cu layer at the interface of TI and FM metal provides a new degree of freedom for tuning the SCC efficiency of the topological surface states. The significant enhancement of the measured spin-pumping voltage and the increased linewidth of ferromagnetic resonance absorption spectra due to the insertion of Cu layer at the interface indicate a reduction in spin memory loss at the interface that resulted from the presence of exchange coupling between the surface states of TI and the local moments of FM metal. The temperature dependence (from 8 to 300 K) of the evaluated λIEE data for all the trilayer systems, TI/Cu/FM with different Cu thicknesses, confirms the effect of exchange coupling between the TI and FM layer on the SCC efficiency of the topological surface state. This study offers promising ways for designing more efficient spin-charge conversion devices of the TI-based heterostructure by controlling the interface effects.

Magnon Confinement in an All-on-Chip YIG Cavity Resonator Using Hybrid YIG/Py Magnon Barriers.

Confining magnons in cavities can introduce new functionalities to magnonic devices, enabling future magnonic structures to emulate the established photonic and electronic components. As a proof-of-concept, we report magnon confinement in a lithographically defined all-on-chip YIG cavity created between two YIG/Permalloy bilayers. We take advantage of the modified magnetic properties of the covered/uncovered YIG film to define on-chip distinct regions with boundaries capable of confining magnons. We confirm this by measuring multiple spin-pumping voltage peaks in a 400 nm wide platinum strip placed along the center of the cavity. These peaks coincide with multiple spin-wave resonance modes calculated for a YIG slab with the corresponding geometry. The fabrication of micrometer-sized YIG cavities following this technique represents a new approach to control coherent magnons, while the spin-pumping voltage in a nanometer-sized Pt strip demonstrates to be a noninvasive local detector of the magnon resonance intensity.

Giant spin-to-charge conversion at an all-epitaxial single-crystal-oxide Rashba interface with a strongly correlated metal interlayer.

The two-dimensional electron gas (2DEG) formed at interfaces between SrTiO3 (STO) and other oxide insulating layers is promising for use in efficient spin-charge conversion due to the large Rashba spin-orbit interaction (RSOI). However, these insulating layers on STO prevent the propagation of a spin current injected from an adjacent ferromagnetic layer. Moreover, the mechanism of the spin-current flow in these insulating layers is still unexplored. Here, using a strongly correlated polar-metal LaTiO3+δ (LTO) interlayer and the 2DEG formed at the LTO/STO interface in an all-epitaxial heterostructure, we demonstrate giant spin-to-charge current conversion efficiencies, up to ~190 nm, using spin-pumping ferromagnetic-resonance voltage measurements. This value is the highest among those reported for all materials, including spin Hall systems. Our results suggest that the strong on-site Coulomb repulsion in LTO and the giant RSOI of LTO/STO may be the key to efficient spin-charge conversion with suppressed spin-flip scattering. Our findings highlight the hidden inherent possibilities of oxide interfaces for spin-orbitronics applications.

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.

Study of interfacial spin transport with an antiferromagnetic Cr2O3 interlayer

Interfacial spin transport has been studied in a $\mathrm{YIG}/{\mathrm{Cr}}_{2}{\mathrm{O}}_{3}/\mathrm{Pt}$ trilayer device via the spin-pumping technique. It is found that the linewidths and the magnitudes of the spin-pumping voltage signals suddenly decrease at just below the N\'eel temperature of the ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ interlayer. A detailed analysis shows that the inner decay in the ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ interlayer dominates the interfacial spin transport in a wide temperature range, while the interfacial suppression of pumped spin currents occurs at a temperature slightly lower than the N\'eel temperature, both of which contribute to the sudden changes of spin-pumping voltage signals around the N\'eel temperature. This work carries forward the understanding of the spin transport in an antiferromagnetic system, which would serve to inspire, as well as facilitate, further breakthroughs of the limits of spin-based devices.

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.

Unraveling intricate properties of exchange-coupled bilayers by means of broadband ferromagnetic resonance and spin pumping experiments

Ferromagnetic resonance (FMR) measurements using a broadband microstrip excitation technique were performed at room temperature for an antiferromagnetic/ferromagnetic (AF/FM) bilayer of ${\mathrm{Ir}}_{20}{\mathrm{Mn}}_{80}(35.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}(7.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$. The angular dependence of the resonance field was measured for several excitation frequencies ranging from $1.5$ to $10.0$ GHz. From the numerical fitting of the experimental data, it was observed that the exchange bias field $({H}_{E})$ and the rotatable anisotropy field $({H}_{\mathrm{RA}})$ originating from the exchange interaction at the AF/FM interface are frequency dependent. The results were explained considering the coexistence of ferromagnetic and antiferromagnetic coupling at the AF/FM interface. We also investigated the spin pumping voltage generated in the structure of ${\mathrm{Ir}}_{20}{\mathrm{Mn}}_{80}(35.0\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}(7.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$/Pt(4 nm) and showed that from the voltage peaks occurring at the ferromagnetic resonance condition it is possible to reproduce the FMR dispersion relation.

Electrical manipulation of spin pumping signal through nonlocal thermal magnon transport

We study the magnon transport in the nonlocal configuration composed of two Pt strips on top of a yttrium iron garnet, with and without the presence of RF microwaves generated by an on-chip antenna. We find that the spin-Hall induced thermal magnon heating/cooling, the Oersted field, and the Joule heating generated by the alternating current in the Pt injector can significantly influence the spin-pumping signal measured by the Pt detector in the presence of RF microwaves, forcing the spin-pumping voltage to show up in the first and second harmonic signals in the nonlocal magnon transport measurement. These results indicate that the nonlocal magnon transport configuration can serve as a structure to electrically detect and manipulate the spin-pumping signal. Furthermore, certain caution is needed when studying the interplay between incoherent magnon and coherent magnon spin transport in the nonlocal transport configuration, since the change in microwave-induced spin-pumping voltage can overwhelm the incoherent magnon transport signals.

Observation of High Spin-to-Charge Conversion by Sputtered Bismuth Selenide Thin Films at Room Temperature.

We investigated spin-to-charge conversion in sputtered Bi43Se57/Co20Fe60B20 heterostructures with in-plane magnetization at room temperature. High spin-to-charge conversion voltage signals have been observed at room temperature. The transmission electron microscope images show that the sputtered bismuth selenide thin films are nanogranular in structure. The spin-pumping voltage decreases with an increase in the size of the grains. The inverse Edelstein effect length (λIEE) is estimated to be as large as 0.32 nm. The large λIEE is due to the spin-momentum locking and is further enhanced by quantum confinement in the nanosized grains of the sputtered bismuth selenide films. We also investigated the effect on spin-pumping voltage due to the insertion of layers of MgO and Ag. The MgO insertion layer has almost completely suppressed the spin-pumping voltage, whereas the Ag insertion layer has enhanced the λIEE by 43%.

Nontrivial Nature and Penetration Depth of Topological Surface States in SmB_{6} Thin Films.

The nontrivial feature and penetration depth of the topological surface states (TSS) in SmB_{6} were studied via spin pumping. The experiments used SmB_{6} thin films grown on the bulk magnetic insulator Y_{3}Fe_{5}O_{12} (YIG). Upon the excitation of magnetization precession in the YIG, a spin current is generated in the SmB_{6} that produces, via spin-orbit coupling, a lateral electrical voltage in the film. This spin-pumping voltage signal becomes considerably stronger as the temperature decreases from 150 to 10K, and such an enhancement most likely originates from the spin-momentum locking of the TSS and may thereby serve as evidence for the nontrivial nature of the TSS. The voltage data also show a unique film thickness dependence that suggests a TSS depth of ∼32 nm. The spin-pumping results are supported by transport measurements and analyses using a tight binding model.

Spin pumping and probe in permalloy dots-topological insulator bilayers

We present a ferromagnetic resonance (FMR) spin pumping experiment at room temperature in periodic arrays of permalloy nanodots of different radii deposited onto a 3D topological insulator Bi2Se3 film. We measure the dc voltage signal generated by spin-to-charge conversion of the pumped spin current due to the spin-orbit coupling in the bulk of Bi2Se3. In the nanostructured samples, two resonance peaks are observed, associated with Kittel and inhomogeneous edge modes, respectively. This more complex modal composition in comparison to continuous systems may provide additional advantages for development of prospective spintronic devices. We support our experimental results by theoretical calculations, which are based on micromagnetic modeling of the magnetization dynamics under FMR excitation in a nanodot. A numerical approach to the calculation of the spin-pumping voltage is proposed, and the efficiency of spin-to-charge conversion is estimated for two nanostructured samples with different dot sizes.

Measurement of Spin Pumping Voltage Separated from Extrinsic Microwave Effects

Conversions between spin and charge currents are core technologies in recent spintronics. In this article, we provide methods for estimating inverse spin Hall effects (ISHEs) induced by using microwave-driven spin pumping (SP) as a spin-current generator. ISHE and SP induce an electromotive force at the ferromagnetic or spin-wave resonance, which offers a valuable electric way to study spin physics in materials. At the resonance, a microwave for exciting the magnetization dynamics induces an additional electromotive force via rf-current rectification and thermoelectric effects. We discuss methods to separate the signals generated from such extrinsic microwave effects by controlling sample structures and configurations. These methods are helpful in performing accurate measurements on ISHE induced by SP, enabling quantitative studies on the conversion between spin and charge currents on various kinds of materials.

Long-term potentiation of magnonic synapses by photocontrolled spin current mimicked in reentrant spin-glass garnet ferrite Lu3Fe5−2xCoxSixO12 thin films

(Co,Si)-cosubstituted Lu3Fe5O12 (Lu3Fe5−2xCoxSixO12; 0.00 ≤ x ≤ 1.00) thin films were grown on Y3Al5O12(001) substrates by pulsed laser deposition. Reentrant spin-glass behavior was observed and its robustness against external magnetic fields was improved by increasing the Co–Si content. In contrast, the spectral linewidth of ferromagnetic resonance was broadened by increasing the Co–Si content, which indicates that the Lu3Fe4.8Co0.1Si0.1O12 thin film is an optimal spin-glass spin-wave conductor. The spin pumping voltage of Lu3Fe4.8Co0.1Si0.1O12 exhibited short-term plasticity with photoinduced magnetic anisotropy and long-term potentiation with the photomemory effect, which mimicked the pre- and postsynaptic potentials of biological systems.

Addition and subtraction of spin pumping voltages in magnetic hybrid structures

We report an investigation of the spin pumping voltage generated in bilayers of ferromagnetic/normal metal in which the ferromagnetic layer is yttrium iron garnet or Permalloy and the normal-metal layer is Pt or Ta. We also investigated a special case in which the voltage is detected in single layer of Permalloy under ferromagnetic resonance condition. It is shown that the spin pumping voltage generated in metallic bilayers have contributions from both layers and the resulting voltage depends on the relative signs of charge currents generated by the inverse spin Hall effect. For instance, the spin pumping voltage generated in Ta has the same sign as the one generate in single layer of Permalloy, but contrary to the voltage generated in Pt. When the voltage is measured in shunted metallic bilayers, the resulting voltage can be a sum or a subtraction of the voltages generated in both layers.

Electrical detection of microwave assisted magnetization reversal by spin pumping

Microwave assisted magnetization reversal has been investigated in a bilayer system of Pt/ferromagnet by detecting a change in the polarity of the spin pumping signal. The reversal process is studied in two material systems, Pt/CoFeB and Pt/NiFe, for different aspect ratios. The onset of the switching behavior is indicated by a sharp transition in the spin pumping voltage. At a threshold value of the external field, the switching process changes from partial to full reversal with increasing microwave power. The proposed method provides a simple way to detect microwave assisted magnetization reversal.

Enhanced inverse spin-Hall effect in ultrathin ferromagnetic/normal metal bilayers

Electrically detected ferromagnetic resonance is measured in microdevices patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification voltages are observed and distinguished via their angular dependence. The spin-pumping voltage shows an unexpected increase as the cobalt thickness is reduced below 2 nm. This enhancement allows more efficient conversion of spin to charge current.

Unidirectional anisotropy in the spin pumping voltage in yttrium iron garnet/platinum bilayers

Detailed measurements of the dc voltage generated in a thin Pt layer deposited on films of yttrium iron garnet (YIG) have been carried out to study the spin pumping effect produced by magnetostatic (MS) modes excited by a microwave field. In relatively thick YIG films the modes are far apart so that one can identify clearly the spin pumping voltage in VSP produced by each MS mode. We have discovered that when the sputter deposition of the thin Pt layer is made on the YIG film magnetized by a static magnetic field, VSP exhibits a strong unidirectional anisotropy.