Magnetic Damping Research Articles

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.

Ultrafast Spin Dynamics of Electrochemically Grown Heusler Alloy Films

The electrochemical growth of Heusler alloy film with good morphological quality and crystalline order using single-crystalline substrate is demonstrated. Static magneto optical Kerr effect studies are employed to reveal the surface magnetization reversal of the films. An understanding of the intrinsic nature of the magnetization dynamics in this class of electrochemically grown materials is presented using time-resolved magneto optical Kerr effect measurements, under femtosecond laser excitation. Excitation laser fluence dependence study reveals the ultrafast demagnetization time, fast remagnetization time, and magnetic damping parameter as well as their correlation. © 2021 American Chemical Society. All rights reserved.

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

The dynamic response of magnetically ordered materials to an ultrashort external stimulus depends on microscopic parameters, such as magnetic moment, exchange, and spin–orbit interactions. Whereas it is well established that, in multicomponent magnetic alloys and compounds, the speed of demagnetization and spin switching processes has an element‐specific character, the magnetization damping was assumed to be a universal parameter for all constituent magnetic elements irrespective of their different spin–orbit couplings and electronic structure. Herein, experimental and theoretical evidence for an element‐specific magnetic damping parameter is provided by investigating the ultrafast magnetization response of a high‐anisotropy ferrimagnetic DyCo5 alloy to femtosecond laser excitation. Strikingly different demagnetization and remagnetization dynamics of Dy and Co magnetic moments is revealed by employing femtosecond laser pump–X‐ray magnetic circular dichroism probe measurements combined with atomistic spin dynamics (ASD) simulations using ab initio calculated parameters. These observations, fully corroborated by the ASD simulations, are linked to the element‐specific spin–orbit coupling strengths of Dy and Co, which are incorporated in the phenomenological magnetization damping parameters. These findings can be used as a recipe for tuning the speed and magnitude of laser‐driven magnetic processes and consequently allow control over various dynamic functionalities in multicomponent magnetic materials.

A mechanically stable and tunable cryogenic Fabry-Pérot microcavity.

High-finesse, open-geometry microcavities have recently emerged as a versatile tool for enhancing interactions between photons and material systems with a range of applications in quantum optics and quantum information science. However, mechanical vibrations pose a considerable challenge to their operation within a closed-cycle cryostat, particularly when spatial tunability and free-space optical access are required. Here, we present the design and characterization of a system that can achieve ∼16 pm-rms passive mechanical stability between two high-finesse mirrors with 34% duty cycle while permitting both three-dimensional positioning of the cavity mode and free-space confocal imaging. The design relies on two cascaded vibration isolation stages connected by leaf springs that decouple axial and lateral motion and incorporates tuned-mass and magnetic damping. Furthermore, we present a technique for quantifying cavity length displacements similar to or larger than the cavity linewidth, allowing for the in situ measurement of vibrations with and without active feedback. Our results facilitate operation of a tunable, high-finesse cavity within a closed-cycle cryostat, representing an enabling technology for cavity coupling to a variety of solid-state systems.

Universal field dependence of magnetic resonance near zero frequency

Magnetic resonance is a widely-established phenomenon that probes magnetic properties such as magnetic damping and anisotropy. Even though the typical resonance frequency of a magnet ranges from gigahertz to terahertz, experiments also report the resonance near zero frequency in a large class of magnets. Here we revisit this phenomenon by analyzing the symmetry of the system and find that the resonance frequency ($\omega$) follows a universal power law $\omega \varpropto |H-H_c|^p$, where $H_c$ is the critical field at which the resonance frequency is zero. When the magnet preserves the rotational symmetry around the external field ($H$), $p = 1$. Otherwise, $p=1/2$. The magnon excitations are gapped above $H_c$, gapless at $H_c$ and gapped again below $H_c$. The zero frequency is often accompanied by a reorientation transition in the magnetization. For the case that $p=1/2$, this transition is described by a Landau theory for second-order phase transitions. We further show that the spin current driven by thermal gradient and spin-orbit effects can be significantly enhanced when the resonance frequency is close to zero, which can be measured electrically by converting the spin current into electric signals. This may provide an experimentally accessible way to characterize the critical field. Our findings provide a unified understanding of the magnetization dynamics near the critical field, and may, furthermore, inspire the study of magnon transport near magnetic transitions.

Van der Waals Epitaxy of Co10–xZn10–yMnx+y Thin Films: Chemical Composition Engineering and Magnetic Properties

Topologically protected magnetic skyrmions have raised interest for future spintronics applications. One of the main challenges is the synthesis of room temperature skyrmion-hosting materials that are compatible with thin-film technology. We present an approach to produce strain-free epitaxial thin films of Co10–xZn10–yMnx+y using molecular beam epitaxy. Bulk Co10–xZn10–yMnx+y is known to host skyrmions at room temperature for specific composition ratios. Our substrate consists of graphene on oxidized silicon. The van der Waals interactions of the grown material with graphene prevents covalent bonding and corresponding strain. We show how defects in the graphene foster nucleation that results in three different kinds of morphologies: islands, columns, and merged films. Susceptibility measurements suggest a phase transition close to room temperature. We detect up to three spin waves resonances suggesting relatively low magnetic damping. This growth technique opens a new route for the integration of complex alloys and skyrmionic device concepts with silicon electronics.

Development of Landing Rebound Reduction Mechanism Utilizing Magnetic Damper for Multicopters

This paper proposes a rebound reduction mechanism for landing multicopter. Multicopter applications in the logistics industry are expected to increase owing to the aging of logistics drivers and the decline in their numbers. Currently, most multicopters land on their designated landing pads. However, these pads are not always available at the destination, and landing on rough terrain is needed in such cases. This paper describes the development of a mechanism to reduce rebound during landing, which can easily cause tipping over. The mechanism should be lightweight to ensure that battery power is conserved and that payload transport capability is increased. Simultaneously, the mechanism should be robust against environmental variations because multicopters are used outdoors and under various temperature conditions. A mechanism consisting of a spring and a magnetic damper is proposed and is modeled using multibody dynamics. It is known that the magnetic damper possesses robustness against temperature variations. Moreover, this paper presents the design parameter optimization for the proposed mechanism considering both the rebound reduction effect and weight reduction. The spring constant and viscous damping coefficient of the proposed mechanism are determined via numerical simulations with the electromagnetic simulator JMAG. The effectiveness of the proposed mechanism is verified via vertical freefall simulations. A simple experimental system is used to evaluate the mechanism, and the experimental results indicate that the mechanism is effective.

Magnetoelastic interactions and magnetic damping in Co2Fe0.4Mn0.6Si and Co2FeGa0.5Ge0.5 Heusler alloys thin films for spintronic applications

Co2Fe0.4Mn0.6Si (CFMS) and Co2FeGa0.5Ge0.5 (CFGG) Heusler alloys are among the most promising thin film materials for spintronic devices due to a high spin polarization, low magnetic damping and giant/tunneling magnetoresistance ratios. Despite numerous investigations of Heusler alloys magnetic properties performed up to now, magnetoelastic effects in these materials remain not fully understood; due to quite rare studies of correlations between magnetoelastic and other magnetic properties, such as magnetic dissipation or magnetic anisotropy. In this research we have investigated epitaxial CFMS and CFGG Heusler alloys thin films of thickness in the range of 15–50 nm. We have determined the magnetoelastic tensor components and magnetic damping parameters as a function of the magnetic layer thickness. Magnetic damping measurements revealed the existence of non-Gilbert dissipation related contributions, including two-magnon scattering and spin pumping phenomena. Magnetoelastic constant B11 values and the effective magnetic damping parameter αeff values were found to be in the range of − 6 to 30 × 106 erg/cm3 and between 1 and 12 × 10–3, respectively. The values of saturation magnetostriction λS for CFMS Heusler alloy thin films were also obtained using the strain modulated ferromagnetic resonance technique. The correlation between αeff and B11, depending on magnetic layer thickness was determined based on the performed investigations of the above mentioned magnetic properties.

Temperature dependence of the effective Gilbert damping constant of FeRh thin films

Antiferromagnetic (AFM) materials have attracted attention for device applications due to the absence of the stray field and high-frequency response. To integrate AFM materials into magnetic devices, the understanding of the interfacial effect between AFM and ferromagnetic (FM) materials is required. In particular, magnetization dynamics and magnetic damping are critical phenomena to be elucidated since they govern magnetization switching, spin-wave propagation, etc. Although a conventional method for studying the interfacial effects is stacking materials, the approach may cause unfavorable factors. To get insight into the dynamic properties at the AFM and FM interfaces, we have focused on B2-ordered FeRh, showing the first-order phase transition from the AFM to FM states, since the coexistence of AFM and FM domains occurs during transitions, which is an ideal platform for studying interfacial effects. For this study, we have studied ferromagnetic resonance (FMR) of FeRh thin films during the AFM–FM phase transition as a function of temperature. From the FMR measurements, we characterize the temperature dependence of the effective Gilbert damping constant αeff. We find that αeff decreases with increasing temperature, indicating that the temperature variation of the effective Gilbert damping constant originates from the exchange interaction between the AFM and FM domains in the film and/or AFM domains as a spin sink.

Effects of Interfacial Oxidization on Magnetic Damping and Spin-Orbit Torques.

We investigate the effects of interfacial oxidation on the perpendicular magnetic anisotropy, magnetic damping, and spin-orbit torques in heavy-metal (Pt)/ferromagnet (Co or NiFe)/capping (MgO/Ta, HfOx, or TaN) structures. At room temperature, the capping materials influence the effective surface magnetic anisotropy energy density, which is associated with the formation of interfacial magnetic oxides. The magnetic damping parameter of Co is considerably influenced by the capping material (especially MgO) while that of NiFe is not. This is possibly due to extra magnetic damping via spin-pumping process across the Co/CoO interface and incoherent magnon generation (spin fluctuation) developed in the antiferromagnetic CoO. It is also observed that both antidamping and field-like spin-orbit torque efficiencies vary with the capping material in the thickness ranges we examined. Our results reveal the crucial role of interfacial oxides on the perpendicular magnetic anisotropy, magnetic damping, and spin-orbit torques.

Resonant enhancement of magnetic damping driven by coherent acoustic phonons in thin Co2FeAl film epitaxied on GaAs

The magnetic dynamics of a thin Co2FeAl film epitaxially grown on GaAs substrate was investigated using the time- resolved magneto-optical Kerr measurement under an out-of-plane external field. The intrinsic magnetic damping constant, which should do not vary with the external magnetic field, exhibits an abnormal huge increase when the precession frequency is tuned to be resonant with that of the coherent longitudinal acoustic phonon in the Co2FeAl/GaAs heterostructure. The experimental finding is suggested to result from the strong coherent energy transfer from spins to acoustic phonons via magnetoelastic effect under a resonant coupling condition, which leads to a huge energy dissipation of spins and a greatly enhanced magnetic damping in Co2FeAl. Our experimental findings provide an experimental evidence of spin pumping-like effect driven by propagating acoustic phonons via magnetoelastic effect, suggesting an alternative approach to the possible long-range spin manipulation via coherent acoustic waves.

Large enhancement of magnetic damping in the presence of domain walls in spin valves

Magnetic damping of the free layer of CoFeB in the spin valve IrMn/CoFe/Cu/CoFeB with large exchange bias has been characterized by frequency-swept ferromagnetic resonance under a series of fixed magnetic fields. The damping constant shows little difference between the parallel and antiparallel magnetization configurations, consistent with the theoretical prediction. Remarkably, in the intermediate states of the pinned CoFe layer under reversal, the effective damping constant of the CoFeB layer is significantly enhanced from 0.0119 up to 0.0292. This enhancement, exceeding the effect of the pumped spin current appreciably, is mainly due to the inhomogeneous broadening and/or two-magnon scattering caused by the stray field emerging from the domain walls (DW) of the pinned CoFe layer when its magnetization is partially reversed. Meanwhile, a resonance frequency shift is also observed in the presence of DW. Our result confirms the strong influence of the pinned layer DW on the magnetic damping in spin valves, which should be properly excluded while dealing with the nonlocal spin-transport-induced damping in heterostructures.

Shape effect on MHD flow of time fractional Ferro-Brinkman type nanofluid with ramped heating

The colloidal suspension of nanometer-sized particles of Fe3O4 in traditional base fluids is referred to as Ferro-nanofluids. These fluids have many technological applications such as cell separation, drug delivery, magnetic resonance imaging, heat dissipation, damping, and dynamic sealing. Due to the massive applications of Ferro-nanofluids, the main objective of this study is to consider the MHD flow of water-based Ferro-nanofluid in the presence of thermal radiation, heat generation, and nanoparticle shape effect. The Caputo-Fabrizio time-fractional Brinkman type fluid model is utilized to demonstrate the proposed flow phenomenon with oscillating and ramped heating boundary conditions. The Laplace transform method is used to solve the model for both ramped and isothermal heating for exact solutions. The ramped and isothermal solutions are simultaneously plotted in the various figures to study the influence of pertinent flow parameters. The results revealed that the fractional parameter has a great impact on both temperature and velocity fields. In the case of ramped heating, both temperature and velocity fields decreasing with increasing fractional parameter. However, in the isothermal case, this trend reverses near the plate and gradually, ramped, and isothermal heating became alike away from the plate for the fractional parameter. Finally, the solutions for temperature and velocity fields are reduced to classical form and validated with already published results.

Large spin Hall angle enhanced by nitrogen incorporation in Pt films

We report on the enhancement of spin Hall angle from the CoFeB/Pt interface by introducing nitrogen into the Pt thin film. Spin-torque ferromagnetic resonance measurements on the effective spin Hall angle (θSH) reveal a non-monotonic variation as a function of the amount of nitrogen gas introduced, Q in the film deposition, which peaks at θSH = 0.16 when Q is 8%. Our analysis shows that the θSH enhancement is mainly attributed to the increase in spin-dependent scattering at the interface. The effective magnetic damping decreases with increasing Q due to the reduced spin–orbit coupling. The interfacial spin transparency is also observed to show improvement after the introduction of nitrogen. Moreover, the additional damping-like torque from the interface may also lead to the enhancement of the linewidth modulation.

High spin mixing conductance and spin interface transparency at the interface of a Co2Fe0.4Mn0.6Si Heusler alloy and Pt

Ferromagnetic materials exhibiting low magnetic damping (α) and moderately high-saturation magnetization are required from the viewpoints of generation, transmission, and detection of spin waves. Since spin-to-charge conversion efficiency is another important parameter, high spin mixing conductance ({g_{r}^{uparrow downarrow}}) is the key for efficient spin-to-charge conversion. Full Heusler alloys, e.g., Co2Fe0.4Mn0.6Si (CFMS), which are predicted to be 100% spin-polarized, exhibit low α. However, g_r^{ uparrow downarrow } at the interface between CFMS and a paramagnet is not fully understood. Here, we report investigations of spin pumping and the inverse spin Hall effect in CFMS/Pt bilayers. Damping analysis indicates the presence of significant spin pumping at the interface of CFMS and Pt, which is also confirmed by the detection of an inverse spin Hall voltage. We show that in CFMS/Pt, g_r^{ uparrow downarrow } (1.70 × 1020 m−2) and the interface transparency (83%) are higher than the values reported for other ferromagnetic/heavy metal systems. We observed a spin Hall angle of ~0.026 for the CFMS/Pt bilayer system.

Magnetic properties of devicelike cobalt/2D materials interfaces

We have studied the magnetism of a cobalt ultrathin film deposited on different two-dimensional (2D) materials, namely graphene, h-BN, and ${\mathrm{WSe}}_{2}$ by the Brillouin light scattering technique. The studied samples are prepared by a pick-up method of large flakes deposited on ${\mathrm{SiO}}_{2}$ and the subsequent physical vapor deposition of metal layers, in a similar way to what is done to make spintronic devices out of such materials. Compared to the reference layer $(\mathrm{Co}/{\mathrm{SiO}}_{2})$, the perpendicular magnetic anisotropy is enhanced in the Co/2D systems, although less than what could be expected on single crystal samples. This result is quantitatively discussed by comparison with ab initio calculations in the case of the Co/graphene interface. We also measure an increase of the magnetic damping and a small Dzyaloshinskii-Moriya interaction in such samples which are discussed with respect to the recent literature.

Topological surface state manipulation of magnetic damping and surface anisotropy in topological insulator/nonmagnet/CoFe heterostructures

The recent advances of high spin-orbit torque efficiency in ferromagnetic/topological insulator (TI) structures hold great promise for the development of high-performance spintronic devices. However, the roles of spin-momentum-locked Dirac surface states (SSs) and the interfacial magnetic proximity effect (MPE) on dynamic magnetic properties are still under debate. Here, we quantitatively distinguish the manipulation effects of SSs and MPE on magnetic damping and surface anisotropy in TI/nonmagnet/CoFe heterostructures. We found that, in addition to the common spin pumping contribution stemming from SSs, damping enhancement also consists of an obvious MPE contribution to the TI/CoFe material system. Moreover, the increased surface magnetic anisotropy for the CoFe films grown on top of a TI layer is believed to arise mainly from the interfacial atomic intermixing. Our paper sheds light on the effects of SSs and MPE on magnetization dynamics, which offer exciting opportunities for developing TI-based spintronics.

Modelling and Test of an Integrated Magnetic Spring-Eddy Current Damper for Space Applications

We present the design, manufacturing, and dynamical characterization of a mechanical suspension made by a passive magnetic spring and an eddy current damper integrated into a single device. Three configurations with 2, 3, and 4 permanent magnets axially distributed with opposite polarizations are designed, simulated, manufactured, and tested. Stiffness of 2410, 2050, 2090 N/m and damping coefficient of 5.45, 10.52 and 17.25 Ns/m are measured for the 2-, 3-, and 4-magnets configurations, respectively. The magnetic suspension provides good mechanical properties combined with excellent cleanness and high reliability, which is very desirable in mechanical systems for space applications.

Numerical Simulation Analysis and Experimental Research on Damping Performance of a Novel Magnetic Fluid Damper

Considering the low‐frequency and large‐amplitude vibration characteristics of the high‐rise structure, a tuned magnetic fluid rolling‐ball damper is proposed to suppress the vibration of the structure. By adjusting the external magnetic field to control the natural rolling frequency of the ball, the purpose of tuning vibration reduction is achieved. Firstly, the working principle of the damper is theoretically analysed, a three‐dimensional (3D) magnetic‐fluid‐solid multiphysical field coupling mathematical model of the damper is established and the governing equations of multiphysical field coupling are derived. Secondly, the magnetic field distribution and operating characteristics of the damper are simulated and analysed. Finally, the effectiveness of the model is verified by experiments, and the damping performance of the damper with two kinds of magnetic fluid is tested and compared. The results show that the magnetic‐fluid‐solid multiphysical field coupling model can accurately simulate the working characteristics of the damper. The maximum damping force of the damper is about 12% of the elastic force of the structure, which can increase the damping ratio of the structure by about two times, effectively reduce the vibration response time, and suppress the vibration of the high‐rise structure.