Magnetic Damping Research Articles

In vacuum dynamic and static tests of a thrust balance for electric propulsion with hysteresis analysis and behaviour prediction with transfer function

This work describes the advances on the development of a thrust-stand for electric propulsion application with a focus on the constraints of the two-stage pulsed plasma thruster (TS-PPT) being developed at INPE at the Electric Propulsion Laboratory (LPEL) of the Laboratory of Combustion and Propulsion (LABCP). While previous work on this instrument focused on basic development in atmospheric pressure the present effort presents the development undertaken to elevate the TRL of the device to allow it to operate in vacuum—the environment where actual electric thrusters operate and are tested. To cater for INPE’s TS-PPT specification, standard masses summing 1.2 kg were used while the electrostatic calibration device (ECD) was set to produce 31 μNs. A detailed hysteresis analysis was carried out at the target TS-PPT specification together with a transfer function that aimed at extrapolating and predicting the behaviour of the instrument. In addition, this work shows the development of a new magnetic damper for the instrument that reduces the waiting time between tests. A new calibration at the TS-PPT specification points were undertaken in vacuum since previous calibration were made for atmospheric pressure and did not include the specific points of interest for the TS-PPT. Furthermore, previous calibration procedures were verified to ensure they would apply to the vacuum conditions and to account for the substitution of some thrust stand previously incompatible vacuum parts and also to account for the addition of the new magnetic damper and other unforeseen conditions caused by the vacuum environment.

Finite Element Analysis to Determine Stiffness, Strength, and Energy Dissipation of U-Shaped Steel Damper under Quasi-Static Loading

In seismic areas, the application of structural dampers becomes compulsory in the design of buildings. There are various types of dampers, such as viscous elastic dampers, viscous fluid dampers, friction dampers, tune mass dampers, yielding/ metallic dampers, and magnetic dampers. All damper systems are designed to protect structural integrities, control damages, prevent injuries by absorbing earthquake energy, and reduce deformation. This paper is a part of research investigating the behaviour of the U-shaped steel damper (as one type of metallic damper) that can be applied to the buildings in seismic areas. The dampers are used as connections between the roof and supporting structure, with the two general purposes. The first is to control the displacement of roof under an earthquake, and the second is to absorb seismic energy through the plasticity of some parts in dampers. If a strong earthquake occurs, the plasticity will absorb the seismic energy; therefore, heavy damage could be avoided from the roof’s mainframes. In this paper, several models of U-shaped steel dampers are introduced. Several parameters, such as elastic stiffness, maximum strength, and energy dissipation, are determined under two conditions. Firstly, static analysis of the proposed damper under variation of U-steel plate configurations, searching the model with more significant energy dissipation. Secondly, static analysis of the unsymmetrical and symmetrical damper under different loading directions. An in-house finite element program that involves both geometrical and material nonlinearities is developed as a problem solver. A quasi-static lateral loading is given to each model until one cycle of the hysteresis curve is reached (in the displacement range between -20 mm to +20 mm). The above parameters are calculated from the hysteresis curve. From the results, the behaviour of the U-steel damper can be described as follows. Firstly, increasing the energy dissipation in the lateral direction can be done by increasing the lateral stiffness of the damper. However, it can reduce the maximum elastic deformation of the damper. Secondly, under the random direction of loading, a symmetrical shape can increase the energy dissipation of the damper.

Unveiling transport properties of Co2MnSi Heusler epitaxial thin films with ultra-low magnetic damping

The family of Co-based Heusler compounds contains promising candidates for spintronic applications regarding their predicted Half-Metal-Magnetic nature, ultra-low magnetic damping coefficients, high curie temperatures and tunable electronic properties. Here we focused on the transport properties of Co2MnSi thin films with thickness in the range of 4-44 nm exhibiting magnetic damping in the 10-4 - 10-3 range. The goals of this study are to examine the impact of the peculiar electronic band structure on the transport properties, to identify the temperature-dependent scattering process, and to extract robust conduction parameters to exploit this material in magnetoelectric devices. In order to undoubtedly correlate all results, the full study has been performed on the same series of samples. Scanning transmission electron microscopy experiments were performed to check the chemically-ordered L21 phase in our films, and also allowed us to identify misfit dislocations generated at the interface with the substrate. The variation of the resistivity with film thickness was measured at different temperatures. The results are examined under the Fuchs and Sondheimer model which allowed us to extract the electron mean free path in Co2MnSi in the temperature range 5 – 300 K. Values for the residual resistivity, Debye temperature, and distance between the Fermi energy and the conduction band for minority spins were obtained from the fit of the resistivity versus temperatures curves. A negative AMR ratio was measured for all the samples which confirmed the Half-metallic nature of the Co2MnSi films. The determination of the ordinary Hall coefficient alloys allowed us to extract the carrier concentration and carrier mobility and their dependency on the temperature. Finally, scaling of the anomalous Hall coefficient with the longitudinal resistivity was performed indicating that skew scattering is the dominant temperature-dependent scattering mechanism in our films.

Controlling the radiative damping of an on-chip artificial magnon mode

Controlling magnetic damping lies at the heart of spintronic applications. In particular, manipulating the radiative damping of magnons is important for the emerging dissipative magnon–photon coupling and, therefore, opens up possibilities for advanced hybrid magnonic devices, nonreciprocal transmission, and topological information processing. The materials or structures that produce magnon modes can be further enriched with an artificial magnon mode produced in a complementary electric inductive–capacitive (CELC) resonator due to its flexible tunability, miniaturized size, and easy integration. Here, we explore the radiative linewidth broadening and frequency shifts of a CELC resonator in an on-chip coplanar waveguide in a self-interfering configuration. The radiative dynamics depends on the magnetic component of the local density of photon states, as well as the intensity, polarization, and boundary conditions. In particular, a voltage-controlled phase shifter was integrated to demonstrate voltage-controlled radiative damping. Adopting both the CELC resonator and its complementary structure may be an effective tool for obtaining the spatial distribution of the electric and magnetic components of microwaves. Our work is a general approach to manipulating the radiative damping of magnetic resonance, which has the potential for on-chip functional devices based on dissipative magnon–photon interactions.

Tuning interfacial spin pump in Ta/CoFeB/MgO films by ultrafast laser pulse

The operation speed and the energy-efficiency of magnetic random access memory (MRAM) is largely controlled by Gilbert damping of magnetic layers. The ultrafast laser pulse may offer an opportunity to tune the interfacial spin pumping, which can then control the Gilbert damping. Here, we have investigated the ultrafast laser induced magnetization precession, especially the magnetic damping, of a series of Ta/CoFeB/MgO thin films using the pump–probe time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. The pump fluence dependence of the magnetic damping has been found to vary with the thickness tCoFeB of the nanoscale CoFeB layer. Remarkably, the intrinsic damping constant α0 has been found to decrease with the increase in the pump fluence when the thickness of the CoFeB layer is less than 1.2 nm. This fluence-dependent behavior of α0 is attributed to the fluence-dependent contribution of the Ta/CoFeB interface induced spin pumping effect. The ultrafast laser pulses effectively enhance the interfacial spin pumping effect via tuning the spin diffusion length of the adjacent Ta layer, from 2.4 to 7.1 nm. Our findings provide insights into the ultrafast laser pulse driven magnetic dynamics and interfacial spin manipulation in Ta/CoFeB/MgO structures.

Design, analysis, control simulation, and experiment of novel electromagnetic hybrid vibration absorber

This paper presents a novel type of electromagnetic hybrid vibration absorber (EHVA) with a double-ring series permanent magnetic circuit applied to improve the two-stage vibration isolation system of marine power machinery. The EHVA comprises a mover with several groups of coils having a series connection, as well as a stator with internal permanent magnets and external permanent magnets, which form a novel magnetic circuit structure based on an improved Halbach array. In this magnet circuit, two adjacent groups of magnetic induction lines overlap at the coil position, thereby strengthening the magnetic field intensity. When the mover moves axially, the coil cuts the magnetic induction line to produce Lorentz force and magnetic damping force. First, the dynamic parameters of the EHVA were calculated based on multi-rigid-body dynamic theory and fixed-point theory. Second, the mechanical and electromagnetic structures of the EHVA were designed. Finally, a test stand was constructed, the system control channel was identified, and the simulation as well as experiment for vibration control using an [Formula: see text] controller were performed. Results indicated that the hybrid vibration reduction system under control reduced the acceleration amplitude by 12.3 dB at 30.6 Hz and achieved better vibration absorption effects between 27 and 33 Hz compared with the uncontrolled system.

Modified Electromagnetic Actuator for Active Suspension System

Active suspension is a type of suspension systems which can vary its damping value in order to adjust the spring firmness in accordance with the road conditions. Real Active Suspension incorporates an external actuator which helps in raising or lowering of vehicle chassis independently at each wheel. Generally, the actuators that are used for active suspension are Hydropneumatic, Electro-hydraulic or Electromagnetic actuators. A new concept of two-way electromagnetic actuation with the help of magnetic damping is proposed in this paper, which can extend its arm on both sides to facilitate active suspension mechanism in both humps and potholes. This increases the ride quality while maneuvering not only in humps, but also in dumps. It also describes about the comparison of spring materials, sophisticated design, construction and working principle of newly proposed actuator. Catia V5 software has been used to design and simulate the actuator model, different spring materials are analyzed and their shear stress and deflections are compared.

Vortex core reversal by elastic waves in ferromagnetic materials

Magnetic vortex has attracted increasing attention due to its potential application in magnetic logic and memory devices. With the development of straintronics, acoustic waves could remotely control the topologically nontrivial magnetic bits such as magnetic vortices. Understanding the dynamic response of magnetic vortex subjected to elastic waves is crucial for the future logic and memory devices. In the present work, a dynamic phase field model is developed to investigate the dynamic magnetoelastic coupling behavior between elastic waves and magnetic vortices. Phase field simulations show that the magnetic vortex core can flip over under the elastic waves with gigahertz frequency. Compared with the results of conventional phase field model without the elastodynamic term, it is found that the strain gradient caused by elastic wave plays an important role in the reversal of vortex core. When the strain gradient in the ferromagnetic material reaches a certain value, the vortex core is likely to flip over. The elastic waves with larger magnitudes and frequencies have the larger strain gradient, which are more easily to cause the reversal of vortex core. In addition to the strain gradient, magnetic damping constant also has great influence on the vortex core reversal by changing the precession process of magnetization. Larger magnetic damping constant makes the smaller precession of magnetization, which retards the reversal of vortex core. The results of this study suggest a mechanical way for the remote control of magnetic vortices by elastic waves.

Development of a moving model rig with a large Reynolds number and measurement of aerodynamic drag

AbstractThe principles and techniques for developing a moving model rig (MMR) driven by compressed air were introduced for moving model tests at large Reynolds numbers (). A corresponding methodology for the accurate measurement of the aerodynamic drag was developed. The main functions of the MMR included the acceleration of the trailer and the model, the deceleration of the trailer, and the deceleration of the model. The acceleration power was provided by the expansion of the compressed air in a pipe, and the deceleration of the model came from the relative motion between the permanent magnet and the static iron deceleration floor. The braking of the trailer was supplied by either a magnetic damping force or the compression of the air in the pipeline by the trailer piston. The free motion of the model in the test section followed the Davis equation. Based on this, a method for the measurement of the model aerodynamic drag using the measured acceleration data was proposed and experimentally demonstrated in an MMR developed in this work.

Second harmonic generation in thin permalloy film

Second harmonic generation versus strength and direction of the applied static magnetic field was measured for a thin permalloy (Ni80Fe20) film in a microstrip line at a driving frequency of 1 GHz and maximum input power of ∼110 mW. The measurements revealed two peaks in the double frequency signal—in the low static field (∼10 Oe) and the high one (∼45 Oe). To explain these findings, a macrospin model of a thin magnetic film with in-plane uniaxial magnetic anisotropy was considered. A perturbation expansion of the Landau–Lifshitz–Gilbert equation provided an explanation of the experimental data. The analysis of the model revealed that the low-field peak was caused by the longitudinal second-order magnetization component and the high-field peak by the transversal one. It was also shown that the uniaxial magnetic anisotropy of the film and the dependence of the magnetic damping parameter on the applied field play an important role in the process of the second harmonic generation. The results obtained give insights into some peculiarities of the nonlinear magnetization dynamics that are important in the development of magnetic film-based devices in the field of microwave signal processing and manipulation.

Element‐Specific Magnetization Damping in Ferrimagnetic DyCo5 Alloys Revealed by Ultrafast X‐ray Measurements

In article number 2100047, Ilie Radu and co-workers provide experimental and theoretical evidence for an element-specific magnetic damping parameter by investigating the ultrafast magnetization response of ferrimagnetic DyCo alloys to femtosecond laser excitation. These novel insights are of utmost importance for understanding the physics of non-equilibrium magnetism as well as for modeling laser-driven magnetic recording phenomena and ultrafast spintronics.

The Gilbert damping of thickness-dependent epitaxial single-crystal Heusler Co2FeAl films at various temperatures

Gilbert damping in epitaxial Heusler Co2FeAl films with thickness varying from 3 nm to 9 nm are investigated by broadband ferromagnetic resonance (FMR) with a temperature range of 5 K–300 K. Gilbert damping shows a continuous decrease with the increasing thickness of Co2FeAl films. Moreover, an enhanced peak of the Gilbert damping is observed with increasing temperature up to approximately 50 K for 3 nm, 6 nm and 9 nm thick Co2FeAl films, which may be attributed to the spin reorientation transition at Co2FeAl/MgO interface. Further, we analyzed the linewidth with a superposition of a uniaxial and a fourfold anisotropy for all samples, which suggests that FMR linewidth in epitaxial Co2FeAl films stems from two-magnon scattering. The change of Gilbert damping is confirmed to originate from various order degrees of the B2 phase with the growth of CFA film, impacting the control of magnetic damping in spin-based nanodevices.

Thermal Control of the Intrinsic Magnetic Damping in a Ferromagnetic Metal

We report experiments on the control of intrinsic magnetic damping by thermal torque effects produced by the spin Seebeck effect and the anomalous Nernst effect in a thin layer of a ferromagnetic metal (Permalloy (Py), ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$). Damping is measured in ferromagnetic resonance (FMR) experiments on a sample excited by microwave radiation and detected by the dc-voltage-generated spin rectification and magnonic charge pumping in the Py film. Application of a temperature gradient in the longitudinal configuration increases or decreases the dc-voltage line width, depending on the sign of the thermal gradient, demonstrating that the magnetic damping in Py is controlled by currents generated by thermal effects. The absolute values of the line-width changes in Py may reach 1 order of magnitude larger than in the ferrimagnetic insulator yttrium iron garnet. The large change in magnetic damping is interpreted as a superposition of different phenomena in the same metallic ferromagnet.

Enhancement of spin-to-charge conversion efficiency in topological insulators by interface engineering

Topological insulator (TI) based heterostructure is a prospective candidate for ultrahigh spin-to-charge conversion efficiency due to its unique surface states. We investigate the spin-to-charge conversion in (Bi,Sb)2Te3 (BST)/CoFeB, BST/Ru/CoFeB, and BST/Ti/CoFeB by spin pumping measurement. We find that the inverse Edelstein effect length (λIEE) increases by 60% with a Ru insertion while remains constant with a Ti insertion. This can be potentially explained by the protection of BST surface states due to the high electronegativity of Ru. Such enhancement is independent of the insertion layer thickness once the thickness of Ru is larger than 0.5 nm, and this result suggests that λIEE is very sensitive to the TI interface. In addition, an effectively perpendicular magnetic anisotropy field and additional magnetic damping are observed in the BST/CoFeB sample, which comes from the interfacial spin–orbit coupling between the BST and the CoFeB. Our work provides a method to enhance λIEE and is useful for the understanding of charge-to-spin conversion in TI-based systems.

Magnetic dynamics of two-dimensional itinerant ferromagnet Fe3GeTe2 * *Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0300803), the National Natural Science Foundation of China (Grant Nos. 11774150, 12074178, 61427812, 11774160, 61805116, and 61271077), and the Natural Science Foundation of Jiangsu Province of China (Grant Nos. BK20192006, BK20180056, and BK20200307).

Among the layered two-dimensional ferromagnetic materials (2D FMs), due to a relatively high T C, the van der Waals (vdW) Fe3GeTe2 (FGT) crystal is of great importance for investigating its distinct magnetic properties. Here, we have carried out static and dynamic magnetization measurements of the FGT crystal with a Curie temperature T C ≈ 204 K. The M–H hysteresis loops with in-plane and out-of-plane orientations show that FGT has a strong perpendicular magnetic anisotropy with the easy axis along its c-axis. Moreover, we have calculated the uniaxial magnetic anisotropy constant (K 1) from the SQUID measurements. The dynamic magnetic properties of FGT have been probed by utilizing the high sensitivity electron-spin-resonance (ESR) spectrometer at cryogenic temperatures. Based on an approximation of single magnetic domain mode, the K 1 and the effective damping constant (α eff) have also been determined from the out-of-plane angular dependence of ferromagnetic resonance (FMR) spectra obtained at the temperature range of 185 K to T C. We have found large magnetic damping with the effective damping constant α eff ∼ 0.58 along with a broad linewidth (Δ H pp > 1000 Oe at 9.48 GHz, H ∥ c-axis). Our results provide useful dynamics information for the development of FGT-based spintronic devices.

Optimized growth of compensated ferrimagnetic insulator Gd3Fe5O12 with a perpendicular magnetic anisotropy* *Project supported by the National Key R&D Program of China (Grant Nos. 2017YFA0206200 and 2016YFA0302300), the Basic Science Center Project of the National Natural Science Foundation of China (Grant No. 51788104), the National Natural Science Foundation of China (Grant Nos. 11774194, 11804182, 51831005, and 11811082), Beijing Natural Science

Compensated ferrimagnetic insulators are particularly interesting for enabling functional spintronic, optical, and microwave devices. Among many different garnets, Gd3Fe5O12 (GdIG) is a representative compensated ferrimagnetic insulator. In this paper, we will study the evolution of the surface morphology, the magnetic properties, and the magnetization compensation through changing the following parameters: the annealing temperature, the growth temperature, the annealing duration, and the choice of different single crystalline garnet substrates. Our objective is to find the optimized growth condition of the GdIG films, for the purpose of achieving a strong perpendicular magnetic anisotropy (PMA) and a flat surface, together with a small effective damping parameter. Through our experiments, we have found that the surface roughness approaching 0.15 nm can be obtained by choosing the growth temperature around 700 °C, together with an enhanced PMA. We have also found the modulation of magnetic anisotropy by choosing different single crystalline garnet substrates which change the tensile strain to the compressive strain. A measure of the effective magnetic damping parameter (α eff = 0.04±0.01) through a spin pumping experiment in a GdIG/Pt bilayer is also made. Through optimizing the growth dynamics of GdIG films, our results could be useful for synthesizing garnet films with a PMA, which could be beneficial for the future development of ferrimagnetic spintronics.

Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers

The magnetic damping constant is a critical parameter for magnetization dynamics and the efficiency of memory devices and magnon transport. Therefore, its manipulation by electric fields is crucial in spintronics. Here, we theoretically demonstrate the voltage-control of magnetic damping in ferro- and ferrimagnetic-insulator (FI)/topological-insulator (TI) bilayers. Assuming a capacitor-like setup, we formulate an effective dissipation torque induced by spin-charge pumping at the FI/TI interface as a function of an applied voltage. By using realistic material parameters, we find that the effective damping for a FI with 10 nm thickness can be tuned by one order of magnitude under the voltage of 0.25 V. Also, we provide perspectives on the voltage-induced modulation of the magnon spin transport on proximity-coupled FIs.

Fabrication Method, Ferromagnetic Resonance Spectroscopy and Spintronics Devices Based on the Organic‐Based Ferrimagnet Vanadium Tetracyanoethylene

AbstractOrganic‐based magnetic materials have been used for spintronic device applications as electrodes of spin aligned carriers and spin‐pumping substrates. Their advantages over more traditional inorganic magnets include reduced magnetic damping and lower fabrication costs. Vanadium tetracyanoethylene, V[TCNE]x (x ≈ 2), is an organic‐based ferrimagnet with an above room‐temperature magnetic order temperature (Tc ≈ 400 K). V[TCNE]x has deposition flexibility and can be grown on a variety of substrates via low‐temperature chemical vapor deposition (CVD). A systematic study of V[TCNE]x thin‐film CVD parameters to achieve optimal film quality, reproducibility, and excellent magnetic properties is reported. This is assessed by broadband ferromagnetic resonance (FMR) that shows most narrow linewidth of ≈1.5 Gauss and an extremely low Gilbert damping coefficient. The neat V[TCNE]x films are shown to be efficient spin injectors via spin pumping into an adjacent platinum layer. Also, under an optimized FMR linewidth, the V[TCNE]x films exhibit Fano‐type resonance with a continuum broadband absorption in the microwave range, which can be readily tuned by the microwave frequency.

Magnetic Damping in Polycrystalline Thin-Film Fe−V Alloys

We report on the magnetic damping properties of polycrystalline $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{V}$ alloy thin films that are deposited at room temperature. By varying the concentration of $\mathrm{V}$ in the alloy, the saturation magnetization can be adjusted from that of $\mathrm{Fe}$ to near zero. We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%--20% $\mathrm{V}$ concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% $\mathrm{V}$. The measured intrinsic damping has a minimum value of (1.53 \ifmmode\pm\else\textpm\fi{} 0.08) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$, which is approximately a factor of 3 higher than our calculated value of 0.48 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$. From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at $\mathrm{V}$ concentrations greater than approximately 35% $\mathrm{V}$ content.

Design and Performance Test of a Magnetic Rate Controlled Stage Damper

In order to control the vibration of civil building structures, a magnetic rate-controlled stage damper (MRCSD) is designed based on a magnetorheological shear thickening fluid (MR-STF). The key technology and performance test of the damper and the parameter identification of the mechanical model are studied. The experimental results show that the main cylinder filled with MR-STF combines the magnetorheological (MR) effect and the shear thickening effect, which has a strong impact on energy dissipation and vibration reduction. Therefore, the designed damper is superior to the traditional viscous damper. With the increase of magnetic field strength, the shear thickening effect of the MR fluid is inhibited and the MR effect is more obvious. The MRCSD can improve the performance of vibration isolation and vibration reduction by controlling damping. Under a different intensity of earthquake, the maximum output can reach 250.2 kN; the mechanical model of the MRCSD is established; and the design parameters of the damper are determined. The theoretical results obtained from the mechanical model of the MRCSD are consistent with the experimental results, which show that the parameter identification method is feasible and effective.