Magnetization Reversal Dynamics Research Articles

Magnetization Dynamics in Quasiperiodic Magnonic Crystals.

Quasiperiodic magnonic crystals, in contrast to their periodic counterparts,
lack strict periodicity which gives rise to complex and localised spin wave spectra
characterized by numerous band gaps and fractal features. Despite their intrinsic
structural complexity, quasiperiodic nature of these magnonic crystals enables better
tunability of spin wave spectra over their periodic counterparts and therefore holds
promise for the applications in reprogrammable magnonic devices. In this article, we
provide an overview of magnetization reversal and precessional magnetization dynamics
studied so far in various quasiperiodic magnonic crystals, illustrating how their
quasiperiodic nature gives rise to tailored band structure, enabling unparalleled control
over spin waves. The review is concluded by highlighting the possible potential
applications of these quasiperiodic magnonic crystals, exploring potential avenues for
future exploration followed by a brief summary.

Crystal structure and peculiarities of microwave parameters of Mg1-xZnxFe2O4 nanospinel ferrites

Employing an advanced citrate precursor methodology, we successfully synthesized nanoscale spinel ferrites, denoted as Mg1-xZnxFe2O4 (where x ranges between 0.0 and 1.0) or MZFO. Comprehensive analysis, utilizing state-of-the-art X-ray diffraction (XRD) techniques, demonstrated the defining attributes of the crystal structure. All examined specimens consistently exhibited a singular phase, adopting a cubic crystalline architecture. XRD pattern analysis allowed us to deduce the average particle dimensions of these ferrite specimens, which span between 17.2 nm and 31.5 nm. This observed size distribution corroborates well with transmission electron microscopy (TEM) imagery estimations. Delving into the Fourier-transform infrared (FTIR) spectra, two distinctive absorption bands of ferrites emerged: the first between 540 and 570 cm−1 and the subsequent between 339 and 435 cm−1. To glean insight into the electromagnetic attributes of MZFO, we meticulously assessed the experimentally ascertained S-parameters. This scrutiny spanned a frequency spectrum of 8–18 GHz. It was inferred that electromagnetic wave energy dissipation arises chiefly from a combination of electrical and magnetic phenomena. The underlying mechanisms of electrical dissipation can be attributed to polarization processes. Concurrently, the magnetic energy losses predominantly stem from magnetization reversal dynamics. Notably, a substantial attenuation observed in the reflected wave energy, ranging between −10 and −18.5 dB, augments the potential for this material's integration into practical applications.

Micromagnetic simulations of emergent monopole defects and magnetization reversal in connected and dipolar Square Artificial Spin Ice

Artificial spin ice (ASI) structures have garnered significant attention due to their unique properties including emergent magnetic monopoles, phase transitions, and collective switching dynamics. In this study, we employ micromagnetic simulations to investigate the magnetic microstates and magnetization reversal dynamics of square ASI with varying connectivity. In particular, we explore an intermediate or a quasi-connected system where the connectivity is altered without significantly changing the strength of dipolar interactions through the introduction of narrow gaps at the vertices. Our results reveal distinct differences in the populations of different vertex types during magnetic reversal for lattices with varying connectivity. These results suggest the possibility of engineering ASI systems in which specific vertex types can be repeatably accessed through adjustments in lattice connectivity.

Micromagnetic Simulation of Irregular Magnetization Reversal Dynamics in a Nanosized Permalloy Film with a Stepped Relief of the Boundary Surface

Micromagnetic Simulation of Irregular Magnetization Reversal Dynamics in a Nanosized Permalloy Film with a Stepped Relief of the Boundary Surface

Effect of thermal annealing on the magnetization reversal and spin dynamics in ferrimagnetic TbCo thin films

“Ferrimagnetic rare earth-transition metal alloys are promising materials for high-speed and low-power spintronic device applications due to their wide tunability in magnetic properties as a function of temperature and composition. Here, we report the influence of thermal annealing on the magnetization reversal and spin dynamics of ferrimagnetic Tb10Co90 thin films. We have used the co-sputtering technique for the deposition of two different thicknesses (20 nm and 25 nm) of the TbCo films. Annealing of the samples has been carried out in the vacuum at 350 °C for 1 h. The magnetization reversal and dynamic properties of the as-deposited and annealed films are studied using the magneto-optical Kerr effect and broadband ferromagnetic resonance measurements at room temperature, respectively. The hysteresis loops reveal an anisotropic reversal process. The anisotropy field reduces from 66 Oe to 38 Oe for 20-nm-thick films and 98 Oe to 31 Oe for 25-nm-thick films upon annealing. Consequently, thermal annealing has led to a large reduction (∼70 %) in inhomogeneous linewidth broadening of the ferromagnetic resonance modes. Gilbert damping constant is found to decrease from 0.027 to 0.021 for 20-nm-thick films, whereas it decreases from 0.043 to 0.019 for 25-nm-thick films. The results have been attributed to the enhanced crystallinity of the films as observed in the structural analysis using grazing incidence X-ray diffraction.”

Annealing dependence on magnetization dynamics and two-magnon scattering in Co40Fe40B20 thin films

Investigation of magnetization dynamics of low-damping ferromagnetic layers is of paramount interest for the realization of spin-based electronic devices. Here, we report the effect of surface oxidation on the structural properties, magnetization reversal and spin dynamics of Co40Fe40B20 (CFB) films. X-Ray diffraction results show that both as-deposited and annealed CFB layers up to 250 °C exhibit an amorphous state. Partial crystallization of CoFe is observed in CFB films above 350 °C. Magnetization reversal curves measured using longitudinal magneto-optic Kerr effect indicate a characteristic square loop along the easy axis for all samples. Ferromagnetic resonance (FMR) results show that the resonance field (Hr) shifts due to changes in the structural phase or microstructure. FMR linewidth (ΔH) is linear for both as-deposited and all annealed CFB above 10 GHz, whereas anomalous behaviour in ΔH as a function of frequency is observed below 10 GHz frequency for annealed thin films. The extracted damping parameter manifests extrinsic contributions in the annealed samples compared to the as-deposited. Angular-dependant FMR results show ΔH and Hr exhibit opposite trends in CFB film annealed at 450 °C due to the presence of inhomogeneities. It suggests the signature of two-magnon scattering in the 450 °C annealed CFB. Our systematic study helps in the understanding of the effect of annealing on the crystallinity and magnetization dynamics in CFB thin films.

Inertial magnetization dynamics on femtosecond scale

Inertia effect should be considered in ferromagnet magnetization dynamics on a sub picosecond-to-femtosecond-time scale. The inertia effect can be described by the inertial Landau-Lifshitz-Gilbert equation. This paper mainly introduces some theoretical and experimental developments of ultrafast ferromagnetic resonance, magnetization reversal and inertial spin dynamics. These results will be helpful in better understanding the basic mechanism of ultrafast demagnetization and magnetization reversal, and deepen the understanding of the microscopic mechanism of magnetic inertia. In the end, the development trend of future experimental and theoretical research are also presented.

Effect of Annealing on Magnetization Reversal and Spin Dynamics in Co40Fe40B20 Thin Films

Effect of Annealing on Magnetization Reversal and Spin Dynamics in Co40Fe40B20 Thin Films

Sheet thickness dependence of magnetization properties based on domains and walls within the non-linear diffusion-like equation for grain-oriented electrical steels

The definition and development of a dynamic or transient magnetic formulation compatible with the Finite Element Method, able to take the dynamic hysteresis and classical and extra losses into account (not a posteriori but a priori), and using the most adapted state variable that makes the problem well defined and easily convergent requires the knowledge of dynamic behavioral properties of soft magnetic materials whatever the thickness and the working conditions. The dynamic hysteresis of soft magnetic materials corresponds to excess iron losses, due to dynamic magnetization reversal processes within magnetic domains and especially to microscopic eddy currents around the magnetic walls in motion and inside rotating domains. The model properties used are the internal quasi-static permeability μ and the dynamic magnetization property Λ that lumps the magnetization mechanisms (domain walls displacement, bowing, fusion, nucleation and multiplication). The latter are involved in the magnetic field damping due to microscopic eddy currents within the field diffusion that renders the magnetic behavior geometry dependent. This model does not separate the field diffusion process from the magnetization reversal mechanisms. In this paper, the sheet thickness ζ dependence of the dynamic magnetization property Λ(ζ) for a Grain Oriented Electrical Steel (GOES: steel made of 3% Silicon and Iron: SiFe) is analyzed in the Rolling Direction (RD). To this extend, it is proposed to carry out and interpret magnetic measurements on GOES samples with the Epstein frame for four different thicknesses (ζ = 0.23, 0.27, 0.30 and 0.35 mm), but with similar metallurgical and crystallographic properties for the whole specimens. Magnetic properties are first identified at low induction with linear assumptions and at higher induction with non-linearities. It makes it possible to re-compute the dynamic hysteresis loops of the material and to predict the losses whatever the working conditions with frequencies from 50 to 800 Hz. It is found that μ does not depend significantly on the sheet thickness whereas Λ depends on it significantly. Microscopic observation of the magnetic domains width are then performed thanks to the MOIF (Magneto-Optical Indicator Film) technique. It helps us discriminate between three simultaneous origins for the dependence of iron losses to the sheet thickness: a skin-like effect, a domains’ refinement and changes on the walls’ mobility. Results are discussed taking the dipolar magnetic effects, closure domains, the grains and texture and the manufacturing and coating residual stress on the metal surface into account.

Magnetization Reversal Dynamics of a Heusler Alloy Exchange-Coupled with a Synthetic Antiferromagnet

Magnetization Reversal Dynamics of a Heusler Alloy Exchange-Coupled with a Synthetic Antiferromagnet

Angular-dependent dynamic response and magnetization reversal in Fibonacci-distorted kagome artificial spin ice

We have measured the angular dependence of ferromagnetic resonance (FMR) spectra for Fibonacci-distorted, kagome artificial spin ice. The number of strong modes in the FMR spectra depend on the orientation of the applied DC magnetic field. In addition, discontinuities observed in the FMR field-frequency dispersion curves also depend on DC field orientation, and signal a multistep DC magnetization reversal, which is caused by the reduced energy degeneracy of Fibonacci-distorted vertices. The results suggest that the orientation of applied magnetic field and severity of Fibonacci distortion constitute control variables for FMR modes and multistep reversal in future magnonic devices and magnetic switching systems.

Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks

Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks were studied in a series of samples with various CoFeB thicknesses d ranging from 1.24 to 1.60 nm with a step of 0.04 nm, using polar magneto-optical Kerr effect (PMOKE) magnetometry and microscopy. Thickness dependence of the magnetic anisotropy was evaluated and the first and second order anisotropy constants were quantified for each thickness. Accordingly, this dependence was deduced to result in magnetization reorientation from out-of-plane to in-plane through an easy-cone magnetization region (1.39 nm ≤ d ≤ 1.41 nm) as d was increased. PMOKE imaging of the magnetization reversal processes for stacks with out-of-plane easy axis indicated both a significant increase of the density of nucleation centers and a change in domain morphology with increasing d up to the magnetization reorientation thickness. Magnetization reversal dynamics was described by a thermal activation model consistent with a Barkhausen length of about 120 nm. The thinnest films with d = 1.24 and 1.28 nm exhibited straightened narrow stripe domains resulting from magnetic dipolar repulsion. A thorough study of narrow stripe domains was performed via direct and indirect magnetization reversal processes. The application of such structures as spin wave nano-channels could be promising.

Simulation Modeling of Unidirectional Dynamic Remagnetization of Electrical Steel

The problem of modeling unidirectional dynamic remagnetization of electrical steel in periodic modes, in-cluding sinusoidal and non-sinusoidal changes in the average cross-section of the induction sheet, is consid-ered and solved. The relevance of the problem under consideration is determined by the fact that when design-ing semiconductor pulse converters of power supply systems operating in peak load modes, it becomes neces-sary to calculate their characteristics and parameters with a more accurate setting of the magnetic characteris-tics of steel, taking into account the real processes of dynamic magnetization reversal observed in the magnetic circuits of transformers and chokes. The proposed simulation model of dynamic magnetization reversal of a ferromagnet allows us to describe with acceptable accuracy the nonlinear, hysteresis and dynamic properties and characteristics of steel, including hysteresis loops, the main magnetization curves, and losses. The performed modernization of the classical Giles – Atherton(JA) model makes it possible to take into account and approxi-mately describe the eddy currents and magnetic viscosity that appear during dynamic remagnetization. The de-veloped numerical procedure allows you to identify the parameters of the constructed model and configure it. The results of the performed validation of the model using experimental data confirm the possibility of its application to describe the characteristics of electrical steel in dynamic modes of remagnetization.

Perpendicular magnetic anisotropy and magnetization process of ferrimagnetic CoFeB/Tb multilayer films

The perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal process of Tb/CoFeB multilayers have been investigated. The PMA was established near the magnetization compensation point by the antiferromagnetic coupling between Tb and CoFeB layers. By controlling the repetition n of multilayers of CoFeB/Tb, the PMA can be optimized accompanying the change of domain structure due to the different pinning. CoFeB/Tb ferrimagnetic multilayers with PMA could be used to improve spin–orbit torque efficiency and velocity of domain wall motion in spintronic devices.

Multistability of the Magnetization Reversal of a Nanoparticle with Cubic Anisotropy

The dynamics of magnetization reversal of a nanoparticle with cubic magnetic anisotropy by a short Gaussian pulse of a magnetic field has been studied. It has been shown that the character of precession dynamics depends on the parameters of the pulse. Conditions under which the action of the pulse results in one of the possible equilibrium states (six or eight, depending on the sign of the anisotropy constant) of the magnetic moment have been revealed. A transition to each of these states can be implemented by varying either the amplitude or the duration of the pulse.

Особенности импульсного перемагничивания высококоэрцитивного материала на основе наночастиц ε-Fe-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

The magnetic structure of the polymorphic modification of iron oxide ε-Fe2O3 is collinear ferrimagnetic in the range from room temperature to ~ 150 K. Further, with decreasing a temperature in ε-Fe2O3, a magnetic transition occurs, accompanied by a significant decrease in the coercive force HC, and in the low temperature range ε-Fe2O3 is characterized by a complex incommensurate magnetic structure. In this work, we experimentally investigated the processes of dynamic magnetization reversal of ε-Fe2O3 nanoparticles of an average size of 8 nm in the temperature range of 80–300 K, comprising various types of magnetic structure of this iron oxide. A bulk material was studied - xerogel SiO2 with ε Fe2O3 nanoparticles embedded in pores. To measure the magnetic hysteresis loops under dynamic magnetization reversal, a pulsed magnetic field technique of Hmax up to 130 kOe was used, using the method of discharging a capacitor bank through a solenoid. The coercive force of HC during dynamic magnetization reversal noticeably exceeds HC for quasi-static conditions. This is caused by processes of superparamagnetic relaxation of the magnetic moments of particles during pulsed magnetization reversal. In the range from room temperature to ~ 150 K, the rate of change of the external field dH / dt is the main parameter determining the behavior of the coercive force under the conditions of dynamic magnetization reversal. This behavior is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K), when the magnetic structure of ε Fe2O3 is incommensurate, the coercive force during pulsed magnetization reversal already depends on the parameter dH / dt, and is largely determined by the maximum applied field Hmax. Such a behavior, atypical for systems of ferrimagnetic particles, is already caused by dynamic spin processes inside ε-Fe2O3 particles during fast magnetization reversal.

Dynamic susceptibility of a concentrated ferrofluid: The role of interparticle interactions.

The dynamic susceptibility of concentrated ferrofluids of magnetite-kerosene type is studied experimentally to clarify the effect of interparticle interactions on the magnetization reversal dynamics and the ferrofluid relaxation time spectrum. We synthesize six ferrofluid samples, four of which have the same wide particle size distribution with a high (more than 2kT) average energy of magnetic dipole interactions. These samples differ in particle concentration and dynamic viscosity. The two remaining samples have a lower content of large particles and a moderate energy of magnetic dipole interactions. For all samples, we measure the dynamic susceptibility in the weak probing field at frequencies up to 160kHz and the field amplitude dependence of the susceptibility at a frequency of 27kHz. The results show that the susceptibility dispersion at frequencies up to 10kHz is due to the rotational diffusion of colloidal particles and aggregates. Steric and hydrodynamic interparticle interactions are the main reason for the strong concentration dependence of the viscosity and so they also strongly influence the frequency dependence of the susceptibility. The influence of van der Waals and magnetic dipole interactions on the susceptibility is manifested indirectly, through the formation of multiparticle clusters. The contribution of clusters to the low-frequency susceptibility reaches 80%. Their large sizes (about 100 nm) shift the dispersion region to frequencies of 1-100Hz, depending on the temperature and particle concentration. Experiments at 27kHz demonstrate the increase in the dynamic susceptibility with increasing field amplitude. This growth is unexpected since all spectral amplitudes in the Debye function expansion of the dynamic susceptibility decrease monotonically with increasing field. To clarify the situation, the auxiliary problem of the magnetodynamics of a uniaxial particle in the alternating field is solved numerically. The Fokker-Planck-Brown rotational diffusion equation is used. It is shown that an increase in the field amplitude reduces the anisotropy barrier and the Néel relaxation time of particles and increases the dynamic susceptibility by one to two orders of magnitude compared to the weak-field limit. The calculation results are in qualitative agreement with the experimental data and allow us to propose a consistent interpretation of these data. We find that the increase in dynamic susceptibility with increasing amplitude is observed when two necessary conditions are met: (i) The suspension viscosity and the field frequency are high enough to cause the blocking of the rotational degrees of freedom of particles and aggregates and (ii) particles with a large magnetic anisotropy are present in the ferrofluid.

Synthesis of hydroxyapatite based on coral Banyuwangi using sol-gel method: observe the effect of calcination temperature on its phase and crystallinity

A research on the effect of the calcination temperature on the hydroxyapatite phase and its crystallinity formed has been done. The synthesis method uses sol-gel, for the reason that it can precisely control the composition, the process using low temperature, can produce high purity and homogeneity.The material used is coral from Banyuwangi, East Java. To optimize the forming process, the coral powder was made of 54.84 nm using mechanical high energy milling (HEM-3D) method. Sol-gel methods include hydrolysis, condensation, aging, and drying. The calcination process was then carried out with temperature variations of 450°C, 550°C, 650°C, 700°C, 750°C, 80 °C, 850°C and 900°C. The result of XRD observation shows that the temperature of 550°C gives the optimum hydroxyapatite phase which is 90.8%. In addition, at temperatures below 550°C formed Tricalcium phosphate (TCP), whereas above the temperature formed tetrakalsium phosphate (TTCP). The lower the calcination temperature, the larger the TCP. Conversely, the greater the calcination temperature the greater the TTCP phase. Both phases, both TCP and TTCP are unstable calcium phosphate compounds. The observation results also show that the increase of calcination temperature can increase the degree of crystallinity. The degree of crystallinity of the sample at 900°C is 77.28%, twice the degree of crystallinity of 450°C. In addition, an increase in calcination temperature increases the size of the crystal as well, although the increase is not consistent as the degree of crystallinityIn this study a magnetization reversal dynamics observed in the heat assisted.

Effect of film thickness on magnetic properties of Co/SmCo bilayers

Au/Co/SmCo/Au films with different SmCo and Co thickness were grown on silicon (100) substrates by electron-beam evaporation. The morphology of these films has been analyzed by transmission electron microscopy. The magnetic properties of the bilayers were investigated by magneto-optical Kerr effect. Hysteresis loops show a SmCo/Co single-phase behavior indicating a strong exchange coupling between the soft and hard phases. Also, we have shown that the magnetization reversal dynamics is dominated by domain wall motion.

Dynamics of the magnetic nanoparticles lattice in an external magnetic field

In this paper the processes of quasi-static and dynamic magnetization reversal are studied for square lattices of magnetic nanodipoles with cubic crystallographic anisotropy. The response of the total magnetic moment to the magnetic field pulse of different duration and polarization is determined for different orientational configurations of dipoles. The oscillation modes of the total magnetic moment under alternating magnetic field are also investigated. Regular, quasiperiodic and chaotic oscillatory regimes have been found. The conditions under which oscillations propagate from individual dipoles to the whole system have been revealed.