Magnetic Damping Research Articles

All-optical study of the influence of Co and W stacking sequence on magnetization precession and damping and magnetic anisotropy in asymmetric Pt/(W,Co)/Pt heterostructures

All-optical study of the influence of Co and W stacking sequence on magnetization precession and damping and magnetic anisotropy in asymmetric Pt/(W,Co)/Pt heterostructures

Influence of interface morphology on the magnetic damping of Al-sandwiched Permalloy thin films

Influence of interface morphology on the magnetic damping of Al-sandwiched Permalloy thin films

Effect of Thermal Processing on the Structural and Magnetic Properties of Epitaxial Co2FeGe Films.

The structure and magnetic properties of epitaxial Heusler alloy films (Co2FeGe) deposited on MgO (100) substrates were investigated. Films of 60 nm thickness were prepared by magnetron co-sputtering at different substrate temperatures (TS), and those deposited at room temperature were later annealed at various temperatures (Ta). X-ray diffraction confirmed (001) [110] Co2FeGe || (001) [100] MgO epitaxial growth. A slight tetragonal distortion of the film cubic structure was found in all samples due to the tensile stress induced by the mismatch of the lattice parameters between Co2FeGe and the substrate. Improved quality of epitaxy and the formation of an atomically ordered L21 structure were observed for films processed at elevated temperatures. The values of magnetization increased with increasing TS and Ta. Ferromagnetic resonance (FMR) studies revealed 45° in-plane rotation of the easy anisotropy axis direction depending on the degree of the tetragonal distortion. The film annealed at Ta = 573 K possesses the minimal FMR linewidth and magnetic damping, while both these parameters increase for another TS and Ta. Overall, this study underscores the crucial role of thermal treatment in optimizing the magnetic properties of Co2FeGe films for potential spintronic and magnonic applications.

Chiral Damping of Magnons.

Chiral magnets have garnered significant interest due to the emergence of unique phenomena prohibited in inversion-symmetric magnets. While the equilibrium characteristics of chiral magnets have been extensively explored through the Dzyaloshinskii-Moriya interaction (DMI), nonequilibrium properties like magnetic damping have received comparatively less attention. We present the inaugural direct observation of chiral damping through Brillouin light scattering (BLS) spectroscopy. Employing BLS spectrum analysis, we independently deduce both the DMI and chiral damping, extracting them from the frequency shift and linewidth of the spectrum peak, respectively. The resulting linewidths exhibit clear odd symmetry with respect to the magnon wave vector, unambiguously confirming the presence of chiral damping. Our study introduces a novel methodology for quantifying chiral damping, with potential ramifications on diverse nonequilibrium phenomena within chiral magnets.

Magnetic active mass damper, design and assessment

Magnetic active mass damper, design and assessment

Experimental and numerical study on a multilayer magnetic field rotary eddy current inertial damper

To improve the output damping force of the eddy current damper, a multilayer magnetic field rotary eddy current inertial damper (MMF-RECID) is proposed. The MMF-RECID is an inerter-based eddy current damper. A prototype device of the MMF-RECID is manufactured and tested, and its mechanical properties are systematically investigated. Firstly, the configuration of the MMF-RECID is described, and the calculation formulas of the axial force are derived. Secondly, an MMF-RECID prototype is designed and fabricated, and the apparent mass and energy dissipation performance under recycled axial loading are investigated. Three-dimensional transient numerical simulations of eddy current damping are conducted using the ANSYS Electronics Desktop. The results show that the eddy current damping force exhibits velocity nonlinearity, and the test results are consistent with the simulation results. Next, the study focuses on parameters influencing the maximum eddy current damping torque generated by the copper plate and the corresponding critical rotating speed. These parameters encompass the number and size of the magnets, the thickness of the copper plate, and the air gap. Finally, the earthquake-reduction effect of a six-degree-of-freedom structure equipped with MMF-RECID is analyzed. This study demonstrates that the ball screw system of MMF-RECID achieves a multiplicative effect of apparent mass and eddy current damping force, the eddy current damping force of a multi-layer magnetic field versus a single-layer magnetic field conforms to the law of linear superposition, and the hysteresis curves are stable. The eddy current damping torque can be improved by increasing the number and size of the magnets, and decreasing the air gap. The thickness of the copper plate significantly affects both the maximum damping torque and the critical speed, and the optimal thickness range is between 2 mm and 4 mm.

Effects of spin torque within ferromagnetic infinite medium: The short-wave approximation and Painlevé analysis

In this paper, we investigate the effects of spin-transfer torques within the ferromagnetic infinite medium through the short-wave approximation method. As a result, we have derived the new (1+1) dimensional nonlinear evolution system, which describes the propagation of electromagnetic short waves within the ferromagnet in the presence of electric current density. Using the Painlevé analysis and Hirota’s bilinearization, we unearth the integrability properties of this new evolution system. In the wake of such an analysis, the typical class of excitations and its physical implications are presented. We remark that the current density acts on magnetization like an effective magnetic damping, which is important for the stabilization of magnetic information storage and data process elements.

Performance enhanced magnetic negative stiffness eddy-current damper: Numerical simulation and experimental investigation

Passive negative stiffness dampers (NSDs) possess significant advantages and promising application prospects in the field of structural vibration control. NSDs with high energy dissipation capability are desired to satisfy the vibration mitigation requirements for large-scale engineering structures, such as high-rise buildings and long-span bridges. However, in practical applications, due to the constraints of mounting space and additional weight, the negative stiffness and damping coefficient of existing NSDs are generally not very large and with poor adjustability. To overcome these limitations, this study develops a novel magnetic negative stiffness eddy-current damper (MNSECD) with enhanced overall performance. This damper consists of a magnetic negative stiffness system (MNSS), a multi-layer-plate-type eddy-current damping system (ECDS) in parallel, and a bidirectional ball screw transmission system. Firstly, different magnetic arrays are designed to optimize the magnetic fields of the MNSECD, and to enhance its magnetic negative stiffness and eddy-current damping without adding extra dimensions and weight. Subsequently, the electromagnetic finite-element models (FEMs) of the MNSECD are established to precisely simulate its magnetic negative stiffness and eddy-current damping forces, and these models are further utilized to elucidate the enhancement mechanism of different magnetic arrays. Finally, based on the numerical simulation results, the best performing magnetic array is selected respectively for the ECDS and MNSS systems to carry out experimental studies on a small-scale prototype. Numerical and experimental results indicate that the selected magnetic array for the MNSS proves highly effective in enhancing the magnetic negative stiffness of the MNSECD, while the selected magnetic array for the ECDS also demonstrates superior effectiveness in enhancing the eddy-current damping of the damper. These findings suggest that the novel MNSECD can be readily used in the vibration control of large-scale engineering structures.

Tailoring structural and magnetic properties of NiCu nanowires by electrodeposition

In this work, we investigated the tailoring of structural and magnetic properties of NiCu nanowires through electrodeposition. Continuous (S1) and composition-modulated (S2) wires were fabricated by electrodeposition using porous alumina membranes as a template. Morphological characterization revealed that the total length of the wires was 8 ± 3 µm in both S1 and S2. For the composition-modulated wires, the length of the segments with the lowest and highest Cu concentrations was 1.2 ± 0.4 µm and 226 ± 65 nm, respectively. Mapping by energy dispersive spectroscopy (EDS) revealed that the concentration of copper and nickel varied along the length of the composition-modulated nanowires, while the continuous nanowires contained a relatively constant concentration of both metals. It is demonstrated that the change in Cu concentration along the wire modifies the lattice parameter, average crystallite size (D) and lattice strain (ε) of Ni. This result is pivotal for understanding the magnetic properties of the wires, as nickel is primarily responsible for the magnetic behavior of the wires. From the ferromagnetic resonance (FMR) results, the linewidth and resonance field values for samples S1 and S2 were determined. It was demonstrated that the greater deformation in the nickel lattice in NiCu nanowires increases the angular dependence of the resonance field. Furthermore, the smaller nickel crystallite size was shown to increase spin dispersion and magnetic damping, leading to complex behavior in FMR responses. Finally, it was demonstrated how Cu can influence the magnetic properties such as coercivity (HC) and squareness (MR/MS) of the wires. Overall, this work contributes to understanding the tailoring of structural and magnetic properties of NiCu nanowires through electrodeposition.

The stabilizing effect of temperature and magnetic field on a 2D magnetic Bénard fluids

In this paper we study the stability of a special magnetic Bénard system near equilibrium, where there exists Laplacian magnetic diffusion and temperature damping but the velocity equation involves no dissipation. Without any velocity dissipation, the fluid velocity is governed by the two-dimensional incompressible Euler equation, whose solution can grow rapidly in time. However, when the fluid is coupled with the magnetic field and temperature through the magnetic Bénard system, we show that the solution is stable. Our results mathematically illustrate that the magnetic field and temperature have the effect of enhancing dissipation and contribute to stabilize the fluid.

Contributions of interfacial spin–orbit coupling to magnetic and spintronic properties in AuPt/ferromagnet bilayers

We investigate the relationships between various magnetic and spintronic properties within AuPt/ferromagnet (FM) bilayers (FM = CoFe, CoFeB, Py, and Co). A linear correlation between the volume and surface magnetic anisotropies is identified, potentially influenced by the magnetoelastic effect. The FM thickness dependence of the magnetic damping indicates that spin-memory loss due to the interfacial spin–orbit coupling (ISOC) and spin pumping to the heavy-metal layer contribute little to the damping. Instead, a notable contribution from two magnon scattering to the damping is recognized in AuPt/(Co, CoFe, CoFeB) bilayers, possibly originating from a magnetic inhomogeneity due to the ISOC. In addition, in contrast to the magnetic damping, spin–orbit-torque efficiencies are unlikely related to the ISOC in AuPt/FM systems. This work offers valuable insights into the correlations among magnetic and spintronic parameters arising from the interfaces, ultimately aiding in the advancement of magnetic memory and information processing systems.

Mitigation of Gilbert Damping in the CoFe/CuOx Orbital Torque System.

Charge-spin interconversion processes underpin the generation of spin-orbit torques in magnetic/nonmagnetic bilayers. However, efficient sources of spin currents such as 5d metals are also efficient spin sinks, resulting in a large increase of magnetic damping. Here we show that a partially oxidized 3d metal can generate a strong orbital torque without a significant increase in damping. Measurements of the torque efficiency ξ and Gilbert damping α in CoFe/CuOx and CoFe/Pt indicate that ξ is comparable in the two systems. The increase in damping relative to a single CoFe layer is Δα < 0.002 in CoFe/CuOx and Δα ≈ 0.005-0.02 in CoFe/Pt, depending on CoFe thickness. We ascribe the nonreciprocal relationship between Δα and ξ in CoFe/CuOx to the small orbital-spin current ratio generated by magnetic resonance in CoFe and the lack of an efficient spin sink in CuOx. Our findings provide new perspectives on the efficient excitation of magnetization dynamics via the orbital torque.

Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron

Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron

Epitaxial Fe/Rh bilayers for efficient spin-to-charge conversion

To address the spin pumping in the conventional ferromagnetic/“normal” metal systems, we fabricated 6 nm Fe/1–15 nm Rh epitaxial bilayers and determined the g-factor, magnetic anisotropy, and magnetization damping by combining both 0–40 GHz CPW-based frequency-dependent and cavity-based 9.56 GHz in-plane angular-dependent ferromagnetic resonance measurements at room temperature. Auger electron spectroscopy and low-energy electron diffraction show that Rh grows epitaxially on Fe. The epitaxial bilayers exhibit a high spin mixing conductance gmix↑↓=(2.9±0.2)×1019 m−2 and a spin diffusion length in Rhodium λsd=9.0±1.3 nm. This makes Rh comparable to Pt and Pd in terms of spin pumping and spin transport efficiency at room temperature.

Simulation study of the Gilbert damping in Ni80Fe20/Nd bilayers: comparison with experiments

We present an experimental and computational investigation the Neodymium thickness dependence of the effective damping constant ( αeff ) in Ni 80 Fe 20/Neodymium (Py/Nd) bilayers. The computational results show that the magnetic damping is strongly dependent on the thickness of Nd, which is in agreement with experimental data. Self consistent solutions of the spin accumulation model and the local magnetisation were used in the simulations. It was not possible to obtain agreement with experiment under the assumption of an enhanced damping in a single Py monolayer. Instead, it was found that the enhanced damping due to spin pumping needed to be spread across two monolayers of Py. This is suggested to arise from interface mixing. Subsequently, the temperature dependence of the effective damping was investigated. It is found that, with increasing temperature, the influence of thermally-induced spin fluctuations on magnetic damping becomes stronger with increasing Nd thickness.

Write-error reduction in voltage-driven magnetization switching using a recording layer with low magnetic damping

Write-error reduction in voltage-driven magnetization switching using a recording layer with low magnetic damping

Highly efficient field-free switching of perpendicular yttrium iron garnet with collinear spin current

Yttrium iron garnet, a material possessing ultralow magnetic damping and extraordinarily long magnon diffusion length, is the most widely studied magnetic insulator in spintronics and magnonics. Field-free electrical control of perpendicular yttrium iron garnet magnetization with considerable efficiency is highly desired for excellent device performance. Here, we demonstrate such an accomplishment with a collinear spin current, whose spin polarization and propagation direction are both perpendicular to the interface. Remarkably, the field-free magnetization switching is achieved not only with a heavy-metal-free material, Permalloy, but also with a higher efficiency as compared with a typical heavy metal, Pt. Combined with the direct and inverse effect measurements, we ascribe the collinear spin current to the anomalous spin Hall effect in Permalloy. Our findings provide a new insight into spin current generation in Permalloy and open an avenue in spintronic devices.

Giant anisotropy of magnetic damping in an epitaxial Cr/Fe bilayer with the absence of magnetocrystalline anisotropy

Giant anisotropy of magnetic damping in an epitaxial Cr/Fe bilayer with the absence of magnetocrystalline anisotropy

Stability analysis and vibration suppression in an overhung rotor system using active magnetic damper

The present work demonstrates the effectiveness of an active magnetic damper (AMD) in improving the vibration characteristics of an overhung rotor system (ORS) considering the effects of synchronous mass-unbalance, rotor bow, and viscous internal damping. A finite element-based rotordynamic analysis has been conducted to evaluate the system response using state-space formulation. MATLAB codes are developed for the numerical implementation of the rotordynamic model pertaining to the flexible ORS integrated with an AMD consisting of three parallel feedback loops. The internal damping is found to reduce the vibration amplitudes at the bearing and disk locations. However, it leads to system instability in the absence of AMD beyond the first critical speed (670 RPM) which is indicated by the change in the real part of eigenvalues. Under these circumstances, the use of AMD causes a remarkable improvement and the system stabilizes for almost the entire speed range considered here, 320–10,000 RPM. In addition, the AMD causes a maximum reduction of 95.8%, 96.5%, and 83.3% in the vibration amplitudes at the locations of Bearing 1, Bearing 2, and the overhung disk, respectively. Using an appropriate set of AMD parameters, the system characteristics can be altered effectively as per the requirement.

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.