Magnetic Domain Model Research Articles

Frequency Domain Modeling of a Halbach PM Linear Generator Based Two-Body Point Absorber for Wave Energy Conversion

Point absorbers utilize the relative motion between the floating body and the submerged body to harvest the wave energy. This paper presents the parametric study of a two-body wave energy point absorber to investigate the influence of key design factors. The targeting point absorber employs a slotless Halbach linear generator as the power take-off system to improve the energy conversion efficiency. In this work, we have linearized our developed nonlinear time domain model and presented it in frequency domain to improve the simulation efficiency, where the results of the time domain model and the frequency domain model have been compared. The stochastic linearization method is employed for the first time to linearize the nonlinear dragging effect of a point absorber. The case study suggests that the stiffness of the power take-off system and viscous floater dragging coefficient should be as small as possible and the optimal mass of the bodies should be adopted to achieve the maximum power output. Under the irregular wave condition, the power matrix against the wind speed and the damping coefficient of the power take-off system shows that the optimal damping coefficient is determined by the local weather and geographic condition. Regarding the determinants of the damping coefficient, the factors that affect the power take-off system is investigated. The Halbach PM array length and the coil width should be specially optimized to obtain the desired damping coefficient of the power take-off system at a given point absorber dimension. Lastly, a test-rig has been developed to validate the magnetic domain model.

Modeling of Anomalous Eddy Current Losses Due to Movement of Domain Walls in Particles of a Soft Magnetic Composite

Soft magnetic composites (SMCs) are composed of ferromagnetic particles surrounded by electrical insulation. To establish a homogenization technique for the magnetic field analysis of an electrical machine with an SMC core, we have already proposed a method to evaluate the effective permeability and iron loss of the SMC core using a cell model of one particle taking into account the nonlinear magnetic characteristics and eddy currents. However, the measured eddy current loss cannot be represented by using the proposed method. In this article, a 3-D eddy current analysis method modeling the anomalous eddy current loss due to the movement of domain walls in the cell model is developed based on the Pry and Bean magnetic domain model. The effect of the non-uniformity of the domain structure on the anomalous eddy current loss is investigated. It is shown that the measured eddy current loss can be almost represented by adding the anomalous eddy current loss to the classical one.

Research on stress detection technology of long‐distance pipeline applying non‐magnetic saturation

In order to study the stress detection method on long-distance oil and gas pipeline, the distribution characteristics of the surface remanence signals in the stress concentration regions must be known. They were studied by using the magnetic domain model in the non-magnetic saturation state. The finite element method was used herein with the aim to analyse the static and mechanical characteristics of a ferromagnetic specimen. The variation law of remanence signal in stress concentration regions was simulated. The results show that a residue signal in the stress concentration region exists. In addition, a one-to-one correspondence in the non-magnetic saturation environment is evident. In the case of magnetic saturation, the remanence signal of the stress concentration region is covered and the signal cannot be recognised.

Quantitative study of magnetic memory signal characteristic affected by external magnetic field

In order to study the effects of magnetic memory signals affected by the external magnetic field, the magnetic domain model is used herein to quantify the distribution characteristics of the surface of the magnetic signals linked to the stress concentration areas. By using the method of finite element (FE) analysis, the magneto-mechanical model of X70 pipeline steel was deepened. The change in the rules of magnetic signals in the stress concentration areas subjected to different external magnetic fields was calculated and analyzed, while the systematic research of the experiments was carried out. Research results show that: under the geomagnetic field, there is a one to one linear corresponding relationship between the degree of the stress concentration and the magnetic memory signal. The magnetic memory signal along the different directions changed with the increase of stress, while the trends were different. The ferromagnetic metal components were unsaturated whether the intensity of the external magnetic field was weak, while the intensity of the magnetic field increased with the increase of the magnetic memory signal although the slope of the magneto-mechanics curve decreased. The ferromagnetic metal components were saturated whether the intensity of the external magnetic field was strong, while the magnetic signal on the stress concentration areas was covered and undetectable.

Modeling 2-D Magnetostriction in Nonoriented Electrical Steels Using a Simple Magnetic Domain Model

Magnetostriction in electrical steel is a source of acoustic noise and vibration of rotating electrical machine cores. Magnetostriction of nonoriented (NO) steel under 2-D magnetization is much greater than that under unidirectional, alternating magnetization. An analytical interpretation of the relevance of 2-D magnetostriction and magnetostrictive anisotropy of NO steel based on a simple magnetic domain model is presented. The analysis helps explain the effect of anisotropy on 2-D magnetostriction measurements made on commercial NO steels with different anisotropy factors. The magnitude of the 2-D magnetostriction is shown to depend on the magnetostrictive anisotropy and magnetic Poisson's ratio.

Method of identifying consitutive parameter in Tb0.3Dy0.7Fe2 Alloy

In this paper, a simple consititutive parameter identification method for the application of domain model in Tb0.3Dy0.7Fe2 alloy is studied, the magnetization and hystersis characteristics are summarized. Targeting the problem of unclarity and difficulty in directly testing the constitutive parameters in Tb0.3Dy0.7Fe2 alloy, numerical calculation and experimental test are used to propose a parameter identification method. Coordinate transformation and graphic solution technique are used in this paper to simplify the minimization solutions of domain rotation in alloy. The dependence of parameters in magnetic rotation model is studied. On this basis, combined with simple experimental test, the method of indentifying Tb0.3Dy0.7Fe2 alloy is established, and the influences of anisotropy constants K1 and K2, energy distribution factor ω, axis orientation distribution in domain rotation are discussed. The method can simply and rapidly identify the constitutive parameters of Tb0.3Dy0.7Fe2 alloy in magnetic domain model, which is significant to improve the numerical calculation of domain rotation in magnetostrictive material. The above theoretical computations are significant for establishing magnetomechanical model of magnetostrictive material, and results are helpful for perfecting the identification of constitutive parameters.

Magnetic models of cast amorphous microwires

A theory of a magnetic domain model for glass-coated amorphous microwires is studied. The obtained theoretical results are confirmed by experiments. Cast glass-coated amorphous microwires with positive magnetostriction have a rectangle hysteresis loop, which is characterized by a coercive-force stable magnitude. The coercive-force magnitude and the fluctuations of this magnitude are of theoretical and practical interest. The theory of the relaxation mechanism of magnetic reversal is constructed. For the more precise comparison of the theory and the experiment, a series of experimental measurements is needed, which are also discussed in the paper.

Easy axis reorientation and magneto-crystalline anisotropic resistance of tensile strained (Ga,Mn)As films

We present a study of magnetic anisotropy by using magneto-transport and direct magnetization measurements on tensile strained (Ga,Mn)As films. The magnetic easy axis of the films is in-plane at low temperatures, while the easy axis flips to out-of-plane when temperature is raised or hole concentration is increased. This easy axis reorientation is explained qualitatively in a simple physical picture by Zener’s p–d model. In addition, the magneto-crystalline anisotropic resistance was also investigated experimentally and theoretically based on the single magnetic domain model. The dependence of sheet resistance on the angle between the magnetic field and [1 0 0] direction was measured. It is found that the magnetization vector M in the single-domain state deviates from the external magnetic field H direction at low magnetic field, while for high magnetic field, M continuously moves following the field direction, which leads to different resistivity function behaviors.

Modeling of Magnetic Domain in Grain-Oriented Electrical Steel Sheets based on Multi-directional Magnetostriction Measurements

In this paper, a novel magnetic domain model on grain-oriented electrical steel was established which is based on magnetostriction measurements for an interpretation of the magnetization behavior under rotational magnetization process. The novel model has brought about useful insights for understanding on reconstruction of magnetic domain and kinetics of magnetic domain wall.

Impurity Effect on the Stability of the Ground-State Spin Configuration in Triangular Lattice Antiferromagnet CuFeO2

Effect of impurities on the high-field magnetization process in a frustrated antiferromagnet CuFeO 2 is studied for powder samples of CuFe 1- x Al x O 2 (0≤ x ≤0.1) and CuFe 1- x Cr x O 2 (0≤ x ≤0.08) using a pulse magnet up to 38 T. For the pure Fe compound distinct magnetization anomalies are successively observed at 7, 12 and 20 T due to the field-induced transitions originated from a subtle balance of competing interactions. These anomalies rapidly disappear with increasing impurity concentration. The effect of impurities is interpreted in terms of the magnetic domain model in which the collinear spin structure of the pure system survives locally as domains without coherence as a consequence of partial suppression of a geometrical frustration by impurities.

Mechanism of Matteucci Effect Using Amorphous Magnetic Wires

The mechanism of the sensitive Matteucci effect in negative-magnetostrictive amorphous wires was qualitatively clarified by considering a magnetic domain model and using measurements of BH hysteresis loops for circular magnetization. Three kinds of amorphous wires, FeSiB, CoSiB and FeCo-SiB, with diameters of 50 m and 120 m, were investigated. It was found that the Matteucci voltage was determined by the differential permeability of the BH hysteresis loops, which was highest for FeCoSiB wire with a small negative magnetostriction (? s =0.1×106). Variations in the Matteucci voltage with tension and sample annealing are also explained in terms of the BH characteristics. Three kinds of Matteucci effect were identified, occurring for the cases of (i) an ac wire current, (ii) a perpendicular ac magnetic field, and (iii) a high-frequency wire current and a low-frequency perpendicular ac magnetic field. These effects are the basis of a new data tablet and new rotary encoder.

アモルファス磁性ワイヤのMatteucci効果の発生機構

Mechanism of sensitive Matteucci effect in negative-magnetostrictive amorphous wires was qualitatively clarified considering their magnetic domain model and using measurements of BH hysteresis loops regarding their circular magnetization. Three kinds of amorphous wires of FeSiB, CoSiB and FeCoSiB having diameter of 120-μm and 50-μm were investigated. It was found that the Matteucci voltage was determined by the differential permeability of the BH hysteresis loops which showed the highest value in a slightly negative magnetostrictive FeCoSiB wire (λs=0.1×10-6). Variation characteristics of the Matteucci voltage for applied tension and annealing are also explained using the BH characteristics. Three kinds of Matteucci effects were expressed applying (i) an ac wire current, (ii) a perpendicular ac field and (iii) a high frequency wire current and a low frequency perpendicular ac field. These effects are the basis for the constitution of a new data tablet and new rotary encoder.

磁気・光磁気記録材料への誘い

This is to introduce physical backgrounds on magnetic and magneto-optical recording materials. Firstly, for each theme, fundamental configuration and its function is given. For magnetic recording, the single magnetic domain model, i.e., coherent rotation of magnetization is based on magnetic media and heads, which are applicable for recent items. It is presented that a high coercivity is required for the media from a viewpoint of high density magnetic recording. Special attention is put on a correlation between switching field distribution, SFD in the magnetization reversal and magnetic transition region between recorded domains, which leads to a development principle on materials of recording media. For magnetic heads with magnetic thin film, it is introduced that a decrease in local fluctuation of magnetic anisotropy due to grain size and its distribution is essential function for obtaining a high permeability at 10MHz range. For magneto-optical recording materials, an emphasis is in magnetic multilayer configuration in the recording media for realizing high access time in a disk operation which results in direct overwriting methods. Magnetic field- and light-modulation methods for overwriting are introduced. These contribution due to the film configurations is briefly described.

Magnetic Properties of Au4V Single Crystal

Single crystal of ordered Au 4 V was prepared to reveal the intrinsic magnetic properties. The magnetizations along the three directions [100], [011] and [111] for the original fcc lattice were measured in a temperature range 4.2 K to 300 K under magnetic field up to 90 kOe. A remarkable field cooling effect of the magnetization was interpreted by a crystal and magnetic domain model. Thus the moment ca. 1 µ B per V atom and the large uniaxial anisotropy energy, 1.52×10 7 erg/cm 3 (6.3 cm -1 per V atom), were determined at 4.2 K. The magnetic properties of the poly and single crystals were compared. The electrical resistivities of the ordered and disordered Au 4 V were measured. The origin of the anisotropy and the magnetic property were discussed on a basis of itinerant electron scheme.

A magnetic study of precipitation in a gold-cobalt alloy

Abstract The precipitation kinetics of a gold l·5%, by weight, cobalt alloy have been followed by measuring the saturation magnetization of the precipitated cobalt and the results are compared with current theories. Marked differences were found between the ageing curves of air and water-quenched specimens. The remanent magnetization, coercive force and field to reduce remanence to zero of aged specimens have been measured and the results are discussed in terms of the single magnetic domain model. The magnetic properties are compared with those of the gold nickel system and the conclusion is reached that the dominant contribution to the anisotropy in the gold cobalt system is due to particle shape. In an appendix the remanence curve and coercivity for a random array of single domain ferromagnetic particles having a linear distribution of anisotropies have been calculated and shown to predict the main features of the observed results.