Spin Pumping Effect Research Articles

Self-Induced Spin Pumping and Inverse Spin Hall Effect in Single FePt Thin Films

Self-Induced Spin Pumping and Inverse Spin Hall Effect in Single FePt Thin Films

Optimizing spin pumping in Yttrium Iron Garnet/Platinum bilayers under varying oxygen pressure

Here, we study the influence of magnetic properties on the spin-pumping effect of the Yttrium Iron Garnet/Platinum (YIG/Pt) bilayer. YIG films were deposited by pulsed laser deposition under variable oxygen pressures. Using broadband ferromagnetic resonance techniques, the magnetic properties of the YIG films were measured. We analyzed the spin-pumping effect in these films by measuring damping changes in samples with and without Pt layers, enabling the calculation of spin-mixing conductance. Experimental results show that films prepared at high oxygen pressure exhibit lower magnetization and reduced spin pumping, αsp, leading to a decreased spin mixing conductance, g↑↓. We report a variation in g↑↓ ranging from 4.2×1018 to 15.6×1018,m−2. These findings underscore the sensitivity of spin transport properties to deposition parameters in YIG-based spintronic devices.

In-phase and out-of-phase spin pumping effects in Py/Ru/Py synthetic antiferromagnetic structures

In-phase and out-of-phase spin pumping effects in Py/Ru/Py synthetic antiferromagnetic structures

Charge-spin interconversion in nitrogen sputtered Pt via extrinsic spin Hall effect.

We experimentally investigate the charge-spin interconversion by introducing a lighter impurity, namely nitrogen (N) into Pt by varying the nitrogen gas flow rate,Qfrom 0 to 20%, and studying the Onsager reciprocity of spin Hall effect (SHE) via complementary methods of spin-torque ferromagnetic resonance and spin-pumping inverse SHE measurements, respectively. We notice a reduction in the crystalline nature of Pt upon nitrogen incorporation. We observe the influence of extrinsic side-jump scattering induced SHE by measuring the spin Hall efficiency,θSHin a wide temperature range from 10 to 296 K. This work establishes the incorporation of N in Pt by using sputtering, to enhance the SHE via extrinsic scattering as well as to observe the reciprocal effects of charge-spin interconversion.

Interfacial Magnetic Anisotropy Controlled Spin Pumping in Co60Fe20B20/Pt Stack

Controlled spin transport in magnetic stacks is required to realize pure spin current-driven logic and memory devices. The control over the generation and detection of the pure spin current is achieved by tuning the spin to charge conversion efficiency of the heavy metal interfacing with ferromagnets. Here, we demonstrate the direct tunability of spin angular momentum transfer and thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy. The ultra-low thickness of the CoFeB thin film by tilting the magnetization from in-plane to out-of plane direction due to interfacial anisotropy from higher thickness of CoFeB thin film. The ferromagnetic resonance measurements are performed to investigate the magnetic anisotropy and spin pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density, with varying ferromagnetic layer thickness, is found to increase from 1.10[Formula: see text]MA/m2 to 2.40[Formula: see text]MA/m2, with increasing in-plane anisotropy field. Such interfacial anisotropy-controlled generation of pure spin current can potentially lead to next-generation anisotropic spin current-controlled spintronic devices.

Boundary conditions for micromagnetism with spin currents

In this paper we show how the spin current in insulating ferromagnets can be treated in the micromagnetic framework by generalizing the boundary conditions in order to allow for the transport of magnetic moment and energy at the interface with other spin carrying media. As specific examples we demonstrate the spin Hall torque and spin pumping effects for a ferromagnetic layer in contact with a spin Hall metallic layer. In particular we show how by this method we can reproduce the known literature result in the case of thin films and make predictive examples for thick ferromagnets.

Enhancing Magnetic Damping under GaAs Band-Edge Photoexcitation in a Co2FeAl/n-GaAs Heterojunction.

The ultrafast manipulation of spin in ferromagnet-semiconductor (FM/SC) heterojunctions is a key issue for advancing spintronics, where magnetic damping and interfacial spin transport often define device efficiency. Leveraging selective optical excitation in semiconductors offers a unique approach to spin manipulation in FM/SC heterojunctions. Herein, we investigated the magnetic dynamics of a Co2FeAl/n-GaAs heterojunction using the time-resolved magneto-optical Kerr technique and observed the considerably enhanced magnetic damping of Co2FeAl when GaAs is photoexcited near its band edge. This enhancement is attributed to an enhanced spin-pumping effect facilitated by spin-dependent carrier tunneling and capture within the Co2FeAl layer. Moreover, circularly polarized light excites spin-polarized band-edge photocarriers, further impacting the magnetic damping of Co2FeAl through an additional optical spin-transfer torque on the magnetic moment of Co2FeAl. Our results provide a valuable reference for manipulating spin-pumping and interfacial spin transport in FM/SC heterojunctions, showcasing the advantage of optical control of semiconductor photocarriers for the ultrafast manipulation of magnetic dynamics and interfacial spin transfer.

Realization of Hadamard gate with twisted magnon modes in synthetic antiferromagnets

Manipulating the polarization of spin waves highlights the potential of antiferromagnetic magnonics in encoding and handling magnon information with high fidelity. Here, we propose a flexible approach to mutually convert polarization states (i.e., Hadamard gate) by incorporating a topological degree of freedom, intrinsic orbital angular momentum (OAM), into twisted spin wave modes within synthetic antiferromagnetic nanodisks. The polarization states of spin waves and the implementation of magnonic logic operations can be electrically read out through combined spin pumping and inverse spin Hall effect, as demonstrated by numerical micromagnetic simulations for CoFeB-based synthetic antiferromagnets. Our findings present an exciting possibility of parallel magnonic computing utilizing topologically protected and magnetic damping-resistance OAM of twisted magnons.

Ultrastrong-coupled magnon–polariton in a dynamical inductor based on magnetic-insulator/topological-insulator bilayers

We theoretically study a magnon–polariton in a dynamical inductor consisting of a coil and a bilayer of ferromagnetic insulator (FI) with perpendicular magnetization and a three-dimensional topological insulator (TI). Taking into account the coherent magnetic-dipole (Zeeman) interaction as well as the dissipative spin pumping effect on the FI/TI interface, we formulate a dynamical permeability of the FI/TI bilayer and calculate a corresponding electric admittance of an RLC-circuit. As a result, the spin pumping gives rise to a competitive effect on the modes hybridization, whereas a huge level repulsion due to the coherent coupling, which reaches the ultrastrong coupling regime, is found at room temperature for realistic parameter sets. Our work may open a new avenue for designing on-chip microwave devices based on a magnon–polariton in the RLC-circuit.

Inzhektsiya spina dvizhushcheysya domennoy stenkoy na granitse razdela antiferromagnitnogo izolyatora s dvumernym metallom

A domain wall (DW) which moves parallel to a magnetically compensated interface between an antiferromagnetic insulator (AFMI) and a two-dimensional (2D) metal can pump spin polarization into the metal. It is assumed that localized spins of a collinear AFMI interact with itinerant electrons through their exchange interaction on the interface. We employed the Keldysh formalism of Green’s functions for electrons which experience potential and spin-orbit scattering on random impurities. This formalism allows a unified analysis of spin pumping, spin diffusion and spin relaxation effects on a 2D electron gas. It is shown that the pumping of a nonstaggered magnetization into the metal film takes place in the second order with respect to the interface exchange interaction. At sufficiently weak spin relaxation this pumping effect can be much stronger than the first-order effect of the Pauli magnetism which is produced by the small nonstaggered exchange field of the DW. It is shown that the pumped polarization is sensitive to the geometry of the electron’s Fermi surface and increases when the wave vector of the staggered magnetization approaches the nesting vector of the Fermi surface. In a disordered diffusive electron gas the induced spin polarization follows the motion of the domain wall. It is distributed asymmetrically around the DW over a distance which can be much larger than the DW width.

Static and dynamical behaviour of magnetically coupled Co/Cu/CoFeB trilayers

Engineering the magnetic behaviour of stacks of ferromagnetic and non-magnetic thin films is mainly controlled by the anisotropy of individual layers plus the interlayer exchange coupling constant. Then, Co/Cu/CoFeB trilayers with different Cu layer thicknesses, tCu, were fabricated by sputtering. The effects of tCu on the magnetization reversal processes, the interlayer coupling, FMR frequencies and damping parameters were investigated. The analysis of the hysteresis loops have demonstrated how the two ferromagnetic films can be strongly coupled and behave like a single system for tCu ≤ 3 nm, or like two almost independent or uncoupled layers for tCu ≥ 3 nm. It is shown that the interlayer coupling is at the origin of the observed two FMR resonance modes: the acoustic and the optic modes. Particularly, the resonance frequency of the optic mode is very sensitive to the interlayer coupling constant and high resonance frequencies can be achieved (over 25 GHz) for ferromagnetically coupled Co/CoFeB bilayers with interlayer exchange coupling Jeff = (2.7 ± 0.8) erg/cm2. However, the technological application of such high resonance frequencies of the optic mode can be limited by the increase in the damping parameter mainly due to the spin-pumping effect.

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.

Reduce the magnetic damping of Pt/ferromagnet heterostructures by inserting a Hf spacer layer

We investigated the effect of the Hf spacer layer on the magnetic damping of Pt/ferromagnet (FM) heterostructures by using broadband ferromagnetic resonance. The magnetic damping of Pt/Co is reduced greatly and then enhanced slightly as the thickness of the Hf spacer layer increases, which is ascribed to the competition of the magnetic proximity effect, the anti-damping behavior, and the spin-pumping effect occurring at the interface. The 3-nm-thick Hf spacer layer results in a maximum reduction rate as high as 48.8% for the magnetic damping of the Pt/Co samples. The reduction of magnetic damping by the Hf spacer layer was additionally demonstrated in the heterostructures of Pt/NiFe and Pt/CoFeB, which suggests the universal tuning effect of the Hf spacer layer on the magnetic damping of Pt/FM systems.

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.

Magnetic field modulated ultrafast spin dynamics at Ni80Fe20/Neodymium interface.

Ultrafast spin dynamics is crucial for the next-generation spintronic devices towards high-speed data processing. Here, we investigate the ultrafast spin dynamics of Neodymium/Ni80Fe20 (Nd/Py) bilayers by the time-resolved magneto-optical Kerr effect. The effective modulation of spin dynamics at Nd/Py interfaces is realized by an external magnetic field. The effective magnetic damping of Py increases with increasing Nd thickness, and a large spin mixing conductance (∼19.35×1015 cm-2) at Nd/Py interface is obtained, representing the robust spin pumping effect by Nd/Py interface. The tuning effects are suppressed at a high magnetic field due to the reduced antiparallel magnetic moments at Nd/Py interface. Our results contribute to understanding ultrafast spin dynamics and spin transport behavior in high-speed spintronic devices.

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.

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.

Improvement of the magnon-magnon coupling strength in Y3Fe5O12/Py heterostructures

Magnon-quasiparticle couplings perform magnon information transferences and transports, thus controlling the coupling strengths is significant for novel information function devices. Here, we report the modulation of the magnon-magnon (M−M) coupling strength in Y3Fe5O12/permalloy (YIG/Py) heterostructures via ferromagnetic resonance (FMR) technique. The anti-crossing gap gc enhances 80 Hz by changing the radio frequency (rf) microwave power, which could be ascribed to the enhancement of the dipolar interaction and spin pumping effect. Furthermore, the gc decreases with the increasing angle θ between external magnetic field and rf current due to the increase of magnon relaxation. Moreover, the FMR linewidths change with increasing angle θ due to the magnetic anisotropy parameters and the two-magnon relaxation mechanism induced by the more oblique external field.

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.

Efficient Spin‐to‐Charge Interconversion in Weyl Semimetal TaP at Room Temperature

AbstractIn this paper, spin‐to‐charge current conversion properties in the Weyl semimetal TaP by means of the inverse Rashba–Edelstein effect (IREE) with the interfacial integration of this quantum material with the ferromagnetic metal Permalloy (Py = Ni81Fe19) are presented. The spin currents are generated in the Py layer by the spin pumping effect (SPE) from microwave‐driven ferromagnetic resonance and are detected by a dc voltage along the TaP crystal, at room temperature. A field‐symmetric voltage signal is observed without the contamination of asymmetrical lines due to spin rectification effects observed in studies using metallic ferromagnets. The observed voltage is attributed to spin‐to‐charge current conversion based on the IREE, made possible by the spin–orbit coupling induced intrinsically by the bulk band structure of Weyl semimetals. The measured IREE coefficient λIREE = (0.30 ± 0.01) nm is two orders of magnitude larger than in graphene and is comparable to or larger than the values reported for some metallic interfaces and for several topological insulators.