Effect Of Ferromagnetic Material Research Articles

Effect of Ferromagnetic Materials on Vibration of In-wheel Brushless Direct Current Motor for Light Electric Vehicle

Effect of Ferromagnetic Materials on Vibration of In-wheel Brushless Direct Current Motor for Light Electric Vehicle

Berry curvature induced anomalous Hall effect in Pt2MnGa

The intrinsic anomalous Hall effect in ferromagnetic materials depends on the spin–orbit-coupling-induced effect in the electronic structure. The presence of anomalous Hall effect can be realized from the existence of the finite Berry curvature. Since the Heusler material Pt2MnGa is ferromagnetic in its collinear state and no report on its transport properties has yet been made, the anomalous Hall effect in this system is investigated using a combined approach of the density functional theory and maximally localized Wannier function. Analysis of the Berry curvature reveals positive and negative peaks along the high symmetry k-points. These peaks together lead to a significant negative anomalous Hall conductivity, which makes the material a promising candidate for applications in spintronics.

On the Einstein-de Haas effect in van der Waals microelectromechanical systems

The electric-field–induced gyromagnetic effect in antiferromagnetic 2D films, analogous to the classical Einstein-de Haas effect in ferromagnetic materials, is considered. It is shown that for the micrometer-sized flakes of antiferromagnetic van der Waals materials having a non-diagonal tensor of the magnetoelectric effect, the magnitude of the electrically induced Einstein-de Haas effect is sufficient to be detected with the conventional optical lever approach of an atomic force microscope.

Magnetic moment impact on spin-dependent Seebeck coefficient of ferromagnetic thin films

Magnetic materials may be engineered to produce thermoelectric materials using spin-related effects. However, clear understanding of localized magnetic moments (µI), free carriers, and Seebeck coefficient (S) interrelations is mandatory for efficient material design. In this work, we investigate µI influence on the spin-dependent S of model ferromagnetic thin films, allowing µI thermal fluctuations, ordering, and density variation influence to be independently investigated. µI influence on free carrier polarization is found to be of highest importance on S: efficient coupling of free carrier spin and localized magnetic moment promotes the increase of S, while spin-dependent relaxation time difference between the two spin-dependent conduction channels leads to S decrease. Our observations support new routes for thermoelectric material design based on spin-related effects in ferromagnetic materials.

Gradient Coil Design Method Specifically for Permanent-magnet-type Low Field Portable MRI Brain Scanner

ferromagnetic structures, particularly the anti-eddy plate, in a bi-planar permanent-magnet-type low-field (0.05 T) magnetic resonance imaging (MRI) brain scanner can distort the gradient field in the target region. This study aims to provide a new gradient coil design method that reduces ferromagnetic influences on gradient field linearity. Thus, a simplified model of electromagnetic (EM) structures of the permanent-magnet-type MRI scanners was established. By using precise analytical proof, the anti-eddy plate was reduced to a homogeneous magnetic plate. The overall effects of the EM structures, which can be represented by bi-planar magnetic plates, were evaluated. In sequence, the image magnetic dipole was first introduced to show the effects of anti-eddy plates were added to the conventional equivalent magnetic dipole (EMD) approach. A novel equivalent image magnetic dipole (EIMD) method was proposed to build the gradient coil pattern. The effect of ferromagnetic materials was predicted throughout the gradient coil design phase using the proposed method, and a high-linear gradient field was generated under real working conditions. The computational and experimental results showed that the gradient coil was linear when ferromagnetic structures were present. The effectiveness of the proposed method was demonstrated by comparing T1-weighted images of the conventional method to those of the proposed method. The proposed method reduced image distortion caused by nearby EM structures in bi-planar permanent-magnet-type low-field MRI systems and provided an effective and concise solution for gradient coil designs.

Enhanced anomalous Nernst effects in ferromagnetic materials driven by Weyl nodes

Based on high-throughput (HTP) first-principles calculations, we evaluated the anomalous Hall and anomalous Nernst conductivities of 266 transition-metal-based ferromagnetic compounds. Detailed analysis based on the symmetries and Berry curvatures reveals that the origin of singular-like behavior of anomalous Hall/Nernst conductivities can be mostly attributed to the appearance of Weyl nodes or nodal lines located in the proximity of the Fermi energy, which can be further tailored by external stimuli such as biaxial strains and magnetic fields. Moreover, such calculations are enabled by the automated construction of Wannier functions with a success rate of 92%, which paves the way to perform accurate HTP evaluation of the physical properties such as the transport properties using the Wannier interpolation.

Topological Hall effect in magnetic topological insulator films

Geometric Berry phase can be induced either by spin–orbit coupling, giving rise to the anomalous Hall effect in ferromagnetic materials, or by chiral spin texture, such as skyrmions, leading to the topological Hall effect. Recent experiments have revealed that both phenomena can occur in topological insulator films with magnetic doping, thus providing us with an intriguing platform to study the interplay between these two phenomena. In this work, we report on a numerical simulation of the anomalous Hall and topological Hall effects in a four-band model that can properly describe the quantum well states in the magnetic topological insulator films by combining Landauer–Büttiker formula and the iterative Green’s function method. Our numerical results suggest that spin–orbit coupling in this model plays a different role in the quantum transport in the clean and disordered limits. In the clean limit, spin–orbit coupling mainly influences the longitudinal transport but does not have much effect on topological Hall conductance. In the disordered limit, the longitudinal transport is determined by disorder scattering and spin–orbit coupling is found to affect strongly the topological Hall conductance. This sharp contrast unveils a dramatic interplay between spin–orbit coupling and disorder effect in topological Hall effect in magnetic topological insulator systems.

An Integrated Model of Magnetic Hysteresis, the Magnetomechanical Effect, and the Barkhausen Effect

This article reviews the ferromagnetic hysteresis, magnetomechanical, and Barkhausen properties of magnetic materials and presents an integrated model to describe these effects and the underlying mechanisms that cause these effects. Hysteretic properties of ferromagnets, such as permeability, coercivity, remanence, and hysteresis loss are known to be sensitive to external factors including applied stress, temperature, and heat treatment, and internal factors like residual strain, microstructure, grain size, and anisotropy and the presence of precipitates of a second phase, such as iron carbide in steels. It thus becomes imperative to characterize the effect of these factors on the hysteresis parameters. Currently, several models such as Preisach, Stoner-Wohlfarth, and Jiles-Atherton are used to describe the magnetic hysteresis of ferromagnetic materials. We review here the quasistatic Jiles-Atherton hysteresis model which describes hysteresis in terms of domain wall motion enabling a connection to be made to the physical response of the magnetic material. This model has been extended to include the magnetomechanical effect and the Barkhausen effect in ferromagnetic materials. Theoretical work presented here provides a conceptual framework linking together these magnetic property measurements with model parameters and to the structure of the material.

Analysis of vector hysteresis models in comparison to anhysteretic magnetization model

The design of electrical machines and magnetic actuators requires accurate models to represent hysteresis effects in ferromagnetic materials. The magnetic nonlinearity of the iron core is usually considered by an anhysteretic magnetization curve. With this assumption, hysteresis’ effects in the field computation are completely neglected. This paper presents a comparative study of different hysteresis models, particularly Pragmatic Algebraic Model (PAM) and vector stop model, with regard to a vector anhysteretic anisotropic model. The PAM turns out to be an efficient model implemented with one mathematical equation. The multi cells stop model relies on a consistent thermodynamic formulation, whose dissipation corresponds to a dry friction-like element. Both models implement a constitutive relationship, in which the magnetic flux density vector as independent input and magnetic field strength as output. With a rotational single sheet tester (RSST), various tests for a sample of material FeSi24-50A (FeSi) with a silicon proportion of 2.4 wt% can be proceeded under the application of relevant field distribution. The obtained measured data are applied to parameterize and validate the models. Following numerical experiments the results are compared with those obtained by means of an anhysteretic anisotropic model.

Waiting-time statistics in magnetic systems

Many complex systems, from earthquakes and financial markets to Barkhausen effect in ferromagnetic materials, respond with a noise consisting of discrete avalanche-like events with broad range of sizes and durations, separated by waiting times. Here we focus on the waiting-time statistics in magnetic systems. By investigating the Barkhausen noise in amorphous and polycrystalline ferromagnetic films having different thicknesses, we uncover the form of the waiting-time distribution in time series recorded from the irregular and irreversible motion of magnetic domain walls. Further, we address the question of if the waiting-time distribution evolves with the threshold level, as well as with the film thickness and structural character of the materials. Our results, besides informing on the temporal avalanche correlations, disclose the waiting-time statistics in magnetic systems also bring fingerprints of the universality classes of Barkhausen avalanches and a dimensional crossover in the domain wall dynamics.

Playing with universality classes of Barkhausen avalanches

Many systems crackle, from earthquakes and financial markets to Barkhausen effect in ferromagnetic materials. Despite the diversity in essence, the noise emitted in these dynamical systems consists of avalanche-like events with broad range of sizes and durations, characterized by power-law avalanche distributions and typical average avalanche shape that are fingerprints describing the universality class of the underlying avalanche dynamics. Here we focus on the crackling noise in ferromagnets and scrutinize the traditional statistics of Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films having different thicknesses. We show how scaling exponents and average shape of the avalanches evolve with the structural character of the materials and film thickness. We find quantitative agreement between experiment and theoretical predictions of models for the magnetic domain wall dynamics, and then elucidate the universality classes of Barkhausen avalanches in ferromagnetic films. Thereby, we observe for the first time the dimensional crossover in the domain wall dynamics and the outcomes of the interplay between system dimensionality and range of interactions governing the domain wall dynamics on Barkhausen avalanches.

Universal temporal characteristics and vanishing of multifractality in Barkhausen avalanches.

Barkhausen effect in ferromagnetic materials provides an excellent area for investigating scaling phenomena found in disordered systems exhibiting crackling noise. The critical dynamics is characterized by random pulses or avalanches with scale-invariant properties, power-law distributions, and universal features. However, the traditional Barkhausen avalanches statistics may not be sufficient to fully characterize the complex temporal correlation of the magnetic domain walls dynamics. Here we focus on the multifractal scenario to quantify the temporal scaling characteristics of Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films with thicknesses from 50 to 1000 nm. We show that the multifractal properties are dependent on film thickness, although they seem to be insensitive to the structural character of the materials. Moreover, we observe for the first time the vanishing of the multifractality in the domain walls dynamics. As the thickness is reduced, the multifractal behavior gives place to a monofractal one over the entire range of time scales. This reorganization in the temporal scaling characteristics of Barkhausen avalanches is understood as a universal restructuring associated to the dimensional crossover, from three- to two-dimensional magnetization dynamics.

Performance prediction and analysis of disk-type eddy-current drivers

For the disk-type eddy-current drivers, an accurate and simple performance prediction method is developed. The static field produced by the permanent magnets and induction field by eddy currents are calculated using magnetic equivalent circuit method, and Faraday’s and Ampere’s law, respectively. In this model, many factors, such as the saturation effect of ferromagnetic materials, working temperature and the electromagnetic effects of back iron are taken into consideration. Compared with other methods, the model has a good agreement with three-dimensional finite-element method, and the average error is 4.9%. Finally, a prototype and corresponding test platform are made. Test results show that the proposed method is effective, and the maximum error is less than 8%. Besides, it is confirmed that eddy-current drivers can tolerate shaft misalignment and be used as speeders.

A review of a phenomenological model for magnetocaloric effect in ferromagnetic materials

ABSTRACTThe present work is devoted to a review of the phenomenological model proposed by Mahmoud Aly Hamad (M. Aly Hamad, Phase Transitions 85 (2012) 106–112) to predict the magnetocaloric effect in ferromagnetic material from the only measure of its magnetization as a function of temperature under an applied magnetic field. We questioned the reliability of that model. Based on some experimental data available in the literature, we have shown that, contrary to what is expected, the prediction of the magnetocaloric effect by this model is poor.

Scaling of the Anomalous Hall Effect in Ferrimagnetic Co<sub>90</sub>Gd<sub>10</sub> Thin Films

The anomalous Hall effect in ferromagnetic materials has attracted much attention for more than a century due to its physical complexity and important applications. Depending on its origin, this effect has been explained by three typical mechanisms: intrinsic contribution [1], skew scattering [2], and side jump [3], which cause exponential dependences with different power indexes between the extraordinary Hall conductivity σ xy and the longitudinal conductivity σ xx in experiments [4]. The power law has been extensively studied experimentally in a large series of ferromagnetic materials, by changing the temperature, disorder scattering, and the density of states at the Fermi surface [1].

Evolution of the average avalanche shape with the universality class.

A multitude of systems ranging from the Barkhausen effect in ferromagnetic materials to plastic deformation and earthquakes respond to slow external driving by exhibiting intermittent, scale-free avalanche dynamics or crackling noise. The avalanches are power-law distributed in size, and have a typical average shape: these are the two most important signatures of avalanching systems. Here we show how the average avalanche shape evolves with the universality class of the avalanche dynamics by employing a combination of scaling theory, extensive numerical simulations and data from crack propagation experiments. It follows a simple scaling form parameterized by two numbers, the scaling exponent relating the average avalanche size to its duration and a parameter characterizing the temporal asymmetry of the avalanches. The latter reflects a broken time-reversal symmetry in the avalanche dynamics, emerging from the local nature of the interaction kernel mediating the avalanche dynamics.

Calculation of the energy loss in giant magnetic impedance elements using the complex magnetic permeability spectra

The giant magnetic impedance (GMI) effect in ferromagnetic materials has been investigated for sensing applications. The GMI properties were evaluated via numerical solution of the complex magnetic permeability of the material. MATLAB® simulation was carried out to study the frequency dependence of magnetic permeability via obtaining solutions of the Landau–Lifshitz–Gilbert (LLG) and the Maxwell’s equations. The results indicate that the complex magnetic permeability peaks at a frequency of 6 GHz, corresponding to the ferromagnetic resonant (FMR) frequency, where the energy loss is maximum. A variation of the Gilbert damping parameter (α ) associated with the LLG equation inversely affects this peak value. The area under the curve of complex magnetic permeability, calculated through counting the number of pixels within the image, provides an estimate of the average energy loss density within the material and appears to be consistent with the variation of the peak intensity.

Field application of elasto-magnetic stress sensors for monitoring of cable tension force in cable-stayed bridges

Recently, a novel stress sensor, which utilizes the elasto-magnetic (EM) effect of ferromagnetic materials, has been developed to measure stress in steel cables and wires. In this study, the effectiveness of this EM based stress sensors for monitoring of the cable tension force of a real scale cable-stayed bridge was investigated. Two EM stress sensors were installed on two selected multi-strand cables in Hwa-Myung Bridge, Busan, South Korea. Conventional lift-off test was conducted to obtain reference cable tension forces of two test cables. The reference forces were used to calibrate and validate cable tension force measurements from the EM sensors. Tension force variations of two test cables during the second tensioning work on Hwa-Myung Bridge were monitored using the EM sensors. Numerical simulations were conducted to compare and verify the monitoring results. Based on the results, the effectiveness of EM sensors for accurate field monitoring of the cable tension force of cable-stayed bridge is discussed.

Thermal Effects of Ferroelectric/Magnetic Materials Under Cyclic-Electric Loading

The temperature in the ferroelectric and ferromagnetic materials may rise due to energy dissipation under loading. Thermal effects on the mechanical behavior in ferroelectric/ferromagnetic materials are investigated theoretically in this paper. First, the influence of stresses induced by domain switching on the subsequent domain switching and domain reversal process in ferroelectrics is investigated. Based on the electrical saturation model, the influence of thermal effect on the domain switching is studied, and the changes of stress and electric intensity factors brought by thermal effect are obtained. The accumulative influence of temperature rise on the domain switching zone and fracture behavior of ferroelectrics under cycle electric field is studied. Second, the above approach of ferroelectric materials is extended to analyze the thermal effect in ferromagnetic materials. Using the magnetic saturation model, the temperature fields around the tip of a narrow elliptic hole are calculated under different conditions. It is found that the magnitude of temperature increment strongly depends upon the geometrical shape of the hole, the frequency and wave shape of the magnetic loading. This study is helpful to gain a deep understanding of the fracture and fatigue behavior of ferroelectric/ferromagnetic materials.

Effect of Ferromagnetic Material on the Reduction of Parasitic Emission in Near Field

In this article the results of measurement in near-field concerning a 16-bit microcontroller from Freescale are reported, with and without a film of ferromagnetic material (Permalloy) plated against the surface of its package. This material improves near-field electromagnetic compatibility performances by reducing, in good proportion, the parasitic emission.