Domain Wall Displacement Research Articles

An incremental permeability detection method for yield strength of ferromagnetic materials based on permanent magnet excitation

ABSTRACT In this paper, in order to meet the engineering requirements of mechanical properties detection of materials with low power consumption, a novel incremental permeability detection system based on permanent magnet excitation is proposed to reduce system power consumption. Initially, a new incremental permeability sensor was designed to extract magnetic incremental permeability (MIP) signal. Through finite element simulation, experimental parameters were optimised, and a rational arrangement of double permanent magnets was devised to furnish an optimally strong AC bias field intensity. Subsequently, a practical detection platform was assembled to extract electromagnetic signal features. From the perspective of domain wall displacement, a characteristic value θ was proposed to predict the yield strength, with experimental results yielding a relative error of less than ±10%. These experiments have validated the capability of permanent magnet-type MIP to enable quantitative detection of the yield strength in ferromagnetic materials.

Effects of particle surface modification on magnetic behavior of soft magnetic Fe@SiO2 composites and Fe compacts

The study aims to evaluate the influence of surface modification of Fe powder on the magnetic behavior of soft magnetic compacts and composites that can possibly enhance their properties. The smoothing of ferromagnetic particle surfaces led to a decrease in the total energy loss as the most evident positive impact in all investigated classes (max. by 11% for small, 63–125 μm particle-based annealed Fe compacts, at max. induction 0.5 T and frequency 100 Hz) and to a partial increase in specific electrical resistivity (max. by 47% for small particle-based Fe@SiO2 composites) and resonant frequency (max. by 48% for large, 200–400 μm particle-based Fe@SiO2 composites) as well as partial decrease in coercivity (max. by 14% for small particle-based annealed Fe compacts). Removing surface irregularities negatively affected the maximum total permeability (max. drop by 28% for large particle-based Fe@SiO2 composites) due to increased inner demagnetizing fields. Applying the Bertotti theory for loss separation, we obtained parameters of loss components and assumed the domain structure using simultaneously active magnetic objects as predictors. The total loss decrease observed after the smoothing process originates from the significantly increased numbers of active magnetic objects, facilitating AC magnetization reversal so that domain wall displacements are accompanied by lower energy loss, manifested as a decrease in the excess loss component (max. by 61% for small particle-based Fe@SiO2 composites).

Magnetic loss versus temperature and role of doping in Mn-Zn ferrites

We investigate the effect of different doping schemes on the broadband magnetic losses and their temperature dependence in Mn-Zn ferrites. CaO, Nb2O5, ZrO2, and SiO2 are added with increasing proportions to TiO2-doped prefired powders and, after sintering at either 1275 °C or 1300 °C, the obtained ring samples are tested versus frequency f (DC-1 GHz) and peak polarization Jp (2 mT – 200 mT) up to T = 160 °C. Appropriately enhanced impurity contents are shown to induce further decrease of the energy loss in materials already prepared for best performance at high temperatures (140 – 160 °C). This behavior can be hardly ascribed to the impurity-related increase of the electrical resistivity brough about by extra-doping, being it rather connected to a corresponding monotonical decrease of the effective magnetic anisotropy < Keff > with T. The decreasing anisotropy makes the balance between the contributions of domain wall (dw) displacements and reversible rotations to the magnetization process evolving in favor of the latter. The energy loss correspondingly develops with frequency and peak polarization in a complex fashion, according to the specific dissipative mechanisms sustained by the spins precessing either inside the moving walls or in the bulk. A dividing line in the (Jp − f) plane is identified, which separates dominant dw- and rotation-generated losses. It moves downward (i.e. lower f) with increasing temperature, the higher T the lower the frequency at which the rotations, theoretically assessed via the Landau-Lifshitz equation, supersede the domain wall contribution. Once accomplished, however, the transition to rotations can lead, according to the theoretical model, to higher losses when moving to higher temperatures. Following the experimental trend of the complex resistivity versus frequency at different T values, the calculations and the experiments show that eddy currents start to contribute to the energy loss, in the 5 mm thick ring samples, around a few MHz, accounting for about 50 % of measured loss beyond some 50 MHz. The chief dissipative process at applicative frequencies and induction values is therefore identified with spin damping, to which the generalized loss decomposition method can be applied.

Obtaining extremely low coercivity of high Bs FeCoBSiCPCu nanocrystalline alloys through modulation of magnetic anisotropy

Longitudinal magnetic field annealing is utilized for modifying the magnetic anisotropy and enhancing the magnetic softness of Fe75Co8(B10Si3C3P1)1-x/17Cux (x = 0.5, 0.75, 1, 1.25) nanocrystalline alloys. All of the magnetic field-annealed nanocrystalline alloys with Cu content more than 0.5 at.% exhibit significantly improved soft-magnetic properties, including high saturation magnetic flux density up to 1.87 T, effective permeability of 13,000–16,000 under the condition of 1 A/m and 1 kHz, coercivity as low as 1.6 A/m, and core loss of 0.11–0.45 W/kg under the condition of 1.0 T and 50 Hz. The application of a magnetic field promotes the nucleation and inhibits the growth of grains, leading to an increase in the number density of nanocrystals and the crystalline volume fraction, and a reduction in the grain size. The magnetic field annealing reduces the effective magneto-crystalline anisotropy energy to 2–4 J/m3, and induces longitudinal magnetic anisotropy with anisotropy energy density of 400–900 J/m3 which shows dependence on the crystalline volume fraction. The field-induced magnetic anisotropy dominates over the random local magnetic anisotropies, and results in the formation of regular magnetic domains aligned longitudinally, pinning-free domain wall displacement, and thus enhanced soft-magnetic properties.

Monitoring the Velocity of Domain Wall Motion in Magnetic Microwires.

An approach was proposed to control the displacement of domain walls in magnetic microwires, which are employed in magnetic sensors. The velocity of the domain wall can be altered by the interaction of two magnetic microwires of distinct types. Thorough investigations were conducted utilizing fluxmetric, Sixtus-Tonks, and magneto-optical techniques. The magneto-optical examinations revealed transformation in the surface structure of the domain wall and facilitated the determination of the mechanism of external influence on the movement of domain walls in magnetic microwires.

Wideband loss separation model of nanocrystalline materials considering microscopic magnetization mechanism

The core loss directly determines the performance of high-frequency transformers. This paper presents an enhanced method for calculating core losses by integrating the LLG equation and Maxwell's diffusion equation. By the method, the losses caused by the rotation of the magnetic moment can be obtained. The loss attributed to domain wall displacement is derived from the total loss by subtracting losses due to magnetic moment rotation, further categorized into the hysteresis loss and the residual loss. The observation of the dynamic variation of nanocrystalline magnetic domains with applied excitation verifies the feasibility of the improved method. Finally, the causes of residual loss generation are also analyzed the model accuracy is verified by comparing the measured and modelled values and the traditional loss separation model.

A comprehensive study on MnZn ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting

Manganese-zinc (MnZn) ferrites have important applications in energy conversion, transmission, and harvesting. MnZn ferrite for magnetic field energy harvesting is expected to enhance the saturation magnetic induction (Bs), initial permeability (μi), and Curie temperature (Tc) aspects simultaneously, which is beneficial to the energy harvesting efficiency and safety of the device. In this paper, various formulations of MnZn ferrite samples were prepared by the conventional oxide ceramic process. The cation distribution was determined through Rietveld refinement of XRD patterns Based on this, the M–T curves were fitted by combining Néel molecular field theory with Brillouin functions. The greatest influence on the Curie temperature was found to be the molecular field coefficient between the A and B sites. The magnetization mechanism of MnZn ferrite was comprehensively analyzed by fitting the complex permeability spectrum, magnetocrystalline anisotropy constant, and magnetostriction coefficient. The ratio of domain wall displacement magnetization to domain rotation magnetization shows an increasing and then decreasing trend with Fe content, while |K1| shows an opposite trend. Finally, MnZn ferrite materials with excellent overall performance (Bs = 505mT, μi = 9016, Tc = 447 K) were prepared by investigating the magnetization mechanism.

Effects of magnetic domain morphology on the magnetic spectrum and high‐frequency core losses of MnZn ferrites

AbstractMnZn ferrites that exhibit low core losses at high frequencies are suitable for the integration and miniaturization of power conversion devices. To obtain low core losses at high frequencies, it is important to understand the underlying mechanism. In this work, MnZn ferrites with various grain sizes were produced by changing the sintering temperature. The relationship between domain morphology, dynamic magnetization behavior, and core losses at high frequencies was carefully investigated. As the average grain size approached the critical size of single‐domain state, the contribution of domain wall displacement to complex permeability decreased, while domain wall resonant frequency improved significantly, resulting in the suppression of residual loss at 3 MHz. As the average grain size increased, the domain morphology changed from a single‐domain state to a multidomain state, which increased the initial permeability and decreased hysteresis loss. However, the number of domain walls increased, causing a significant decrease in the domain wall resonant frequency, and resulting in a sharp increase in residual loss. These results provide valuable insights into reducing high‐frequency core losses in MnZn ferrites by domain engineering.

Temperature Dependence of Complex Relative Permeability of the Polycrystalline La0.7Sr0.3MnO3

&lt;p&gt;吾人量測多晶態鑭鍶錳氧變化溫度的電阻率與頻率範圍為 10 kHz 至 10 MHz 的相對複數磁導率特性。樣品室溫電阻率很小，僅為數 m&amp;sdot;Ωcm。電阻率隨著溫度增加，在相轉變溫度 TP = 361 K 附近顯現金屬到半導體的相轉變。室溫量測到的磁譜顯現與磁壁位移有關的鬆弛特性，色散情況非常明顯。隨著溫度升高，磁導率增加，在居禮溫度 TC前達到最大值，然後迅速下降。當溫度從室溫增加，磁壁位移鬆弛頻率 fr幾乎保持不變。當溫度升高到 TC附近，由於磁導率迅速降低，fr劇烈增加。在 TC以上，磁譜的色散現象消失。量測到的 fr與理論值相當符合，可看出磁壁位移的阻滯來源主要源自於渦電流阻滯。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;The temperature-dependent resistivity and complex relative permeability of the polycrystalline La0.7Sr0.3MnO3 have been investigated in the frequency range 10 kHz -10 MHz. The measured room-temperature resistivity is of the order of mcm. As the temperature increases, the resistivity increases and shows a metal-insulator transition. The transition temperature TP is about 361 K. There are pronounced dispersions of the relaxation in the measured spectra, which are due to the domain-wall displacement. The magnitude of permeability increases with increasing temperature, reaches its maximum value near the Curie temperature TC, and then abruptly drops. As the temperature increases, the relaxation frequency fr almost remains a constant value. However, it rapidly increases around TC due to the suddenly decrease of the permeability. The dispersion phenomena of the permeability spectra disappear above TC. The consistence of the measured and calculated fr value shows that the damping factor of domain-wall displacement mainly comes from the eddy current.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Magneto-optical diffraction of visible light as a probe of nanoscale displacement of domain walls at femtosecond timescales.

Using diffraction of femtosecond laser pulses of visible light by a magnetic domain pattern in an iron garnet, we demonstrate a proof of concept of time-resolved measurements of domain pattern movements with nanometer spatial and femtosecond temporal resolution. In this method, a femtosecond laser (pump) pulse initiates magnetization dynamics in a sample that is initially in a labyrinth domain state, while an equally short linearly polarized laser pulse (probe) is diffracted by the domain pattern. The components of the diffracted light that are polarized orthogonally to the incident light generate several concentric diffraction rings. Nanometer small changes in the relative sizes of domains with opposite magnetization result in observable changes in the intensities of the rings. We demonstrate that the signal-to-noise ratio is high enough to detect a 6nm domain wall displacement with 100fs temporal resolution using visible light. We also discuss possible artifacts, such as pump-induced changes of optical properties, that can affect the measurements.

Energy loss and hysteresis of reversible magnetization processes in iron-based soft magnetic composites

The paper focuses on investigation of the hysteresis originating from the reversible magnetization processes and the quantification of the corresponding energy dissipation, on soft magnetic composite materials differing in various parameters so exhibiting different proportions of magnetization processes types during quasi-static magnetizing reversal under different maximum inductions. It was confirmed that reversible magnetization processes show hysteresis too and generate energy losses. These losses come from frictional effects accompanying local rotations of spins at the microscopical view of all magnetization processes including the reversible ones. It was found that the area of a hysteresis loop obtained by the integration of reversible permeability reveals approximately the proportion of reversible magnetization vector rotations, which produce energy loss much more than reversible domain wall displacements.

Magnetoelastic Losses in the Linear Response Region for Three- and Four-Axis Idealized Magnets

In the presented studies, a description of the losses related to relaxation processes in idealized three- and four-axis ferromagnets, as well as ferrites, is considered for the case of a linear response (small perturbations) on the basis of a macroscopic approach. The description takes into account reversible 90° displacements of domain walls (DW) of concentrations (с), ways of DW pinning by linear defects, and processes of DW displacements and rotations of the spontaneous magnetization vector I⃗s, caused by a longitudinal elastic stress wave σ. As a result, the anisotropy of amplitude-independent losses emerges due to displacement processes. Frequency dependence of losses is obtained with consideration of the magnetic symmetry of the crystal, its magnetostructural parameters, and the concentration of magnetic phases ci. The paper also describes the internal frictionn Q-1, the absorption coefficient a, the velocity of propagation of elastic vibrations v and the Δ (1/E)-effect, thus allowing to reveal the texture in the distribution of DWs by their types.&#x0D; It is shown that if the relaxation times of rotation processes τ = β / 2K1 and displacement processes τc = βс / mω20 are the same, then the maxima of the dependence of internal friction on frequency Qc-1(ω) and QB-1(ω) superimpose on each other.&#x0D; The revealed features of magneto-elastic energy dissipation are of interest for laboratory studies and have promising applications in practice for determining the orientation of crystals, describing the texture, and calculating the differential ΔЕ-effect in magnets. The features of the ΔЕ-effect for the considered cases are also revealed.

Nonuniformity of magnetization processes of a cobalt-based amorphous alloys in the as-quenched state

The magnetization processes nonuniformity of an amorphous cobalt-based soft-magnetic alloy AMAG-172 (Co-Ni-Fe-Cr-Mn-Si-B) in the as-quenched state were studied. Studies have shown that the main reason of the magnetic characteristics and magnetization processes nonuniformity is the nonuniformity of internal stresses due to the alloy manufacture method. An indirect characteristic of internal stresses is the domains volume with orthogonal magnetization. The observed bimodal field dependence of the magnetic permeability and the field shift of the hysteresis loops in the region of 180-degree domain walls displacement are a consequence of the nonuniformity of the alloy over its thickness. The field shift and the asymmetry of hysteresis loops are explained in terms of the formation of a unidirectional exchange anisotropy at the interface between the ferromagnetic and antiferromagnetic phases of the planar magnetization components oriented along the ribbon axis. The field shift disappearance and the asymmetry of the hysteresis loops along the width of the tape can be interpreted as a decrease in the thickness of the CoO oxide antiferromagnetic layer due to the difference in the concentrations and depth of oxygen and hydrogen atoms penetration induced into the surface of the tape during the manufacture of the tape as a result of interaction with atmospheric vapor.

Spacer Thickness and Temperature Dependences of the Interlayer Exchange Coupling in a Co/Pt/Co Three-Layer Structure

Domain wall mobility as a function of nonmagnetic interlayer thickness and temperature was studied in ultrathin exchange-coupled ferromagnetic layers using magneto-optic Kerr microscopy. The system under study is a Pt/Co/Pt/Co/Pt heterostructure having perpendicular magnetic anisotropy and a middle Pt layer with spatially variable thickness. The ferromagnetic interaction between the Co layers is observed when the Pt interlayer thickness varies from 5 to 6 nm in a temperature range of 200–300 K. There is a certain interval of Pt layer thickness where domain walls in both ferromagnetic layers move independently. Nonlinear dependence of the domain wall displacement on the applied field was measured. It is shown that an equilibrium position of the relaxed domain wall depends on field, temperature, and the nonmagnetic interlayer thickness. This position is determined by the energy balance: (i) domain wall displacement provided by the applied field, (ii) interlayer exchange interaction in the area swept by the domain wall, and (iii) domain wall coercivity. The mechanism of domain wall stabilization in terms of independent wall motion near critical thickness was considered. It is found that both the coercivity of the Co layer and the critical thickness decrease at higher temperature, while the interlayer exchange constant J is changed weakly.

Transverse domain wall dynamics in hybrid piezoelectric/ferromagnetic devices

This work investigates the static and dynamic features of transverse domain walls in a magnetostrictive, linear elastic isotropic ferromagnetic material under the action of magnetic field (axial and transverse) and electric current. The investigation is done in the framework of the extended Landau–Lifshitz–Gilbert equation by taking into account the effects of stresses induced by a piezoelectric actuator and Rashba spin‐orbit torque caused by structural inversion asymmetry. First, we obtain the expression of magnetization orientation into the two faraway domains, then characterize the static magnetization profile under the action of magnetoelastic and transverse magnetic fields. Next, we introduce a trial function (Schryer and Walker type). After that, by adopting the small angle approximation formalism, we derive the explicit expression of key quantities such as propagating transverse domain wall profile, excitation angle, transverse domain wall velocity, mobility, and displacement. Finally, we present the numerical illustrations of derived analytical results and find that they are in qualitatively good agreement with the recent numerical simulations and experimental observations.

High-performance FeSiAl soft magnetic composites achieved by confined solid-state reaction

Soft magnetic composites (SMCs) consisting of insulated metallic magnetic particles are critical materials in modern electronics. However, the simultaneous optimization of power loss and permeability for SMCs remains challenging due to the vulnerable insulation layer inside. Here, we succeed in fabricating FeSiAl SMC by confined solid-state reaction between TiO2 and FeSiAl matrix, which leads to the formation of homogeneous and lattice-matched Al2O3 layer and brings about effective electrical insulation of FeSiAl particles. TiO2 can progressively release O atoms and confine the solid-state reaction strictly within the interfacial region. Meanwhile, itself becomes ferromagnetic with deficient oxygen, resulting in alleviated magnetic dilution. Fast domain wall displacement and small hysteresis loss are directly observed by in-situ Lorenz transmission electron microscopy. The obtained FeSiAl SMC exhibits low power loss of 130 mW·cm−3 (50 mT, 100 kHz) and high effective permeability of 143, which is desired in energy-saving and high-efficiency devices. This work relates the interfacial behavior with magnetic properties and highlights a new strategy for fabricating high-performance SMCs.

Automation of Kerr microscopy system for domain wall velocity measurements

The present work reports the automation of a Kerr microscopy system for capturing magnetic domains and subsequently measuring the displacement of domain walls (DWs) with pulsed magnetic fields. Suitable algorithms are utilized for enhancing the image contrast, image filtering and the simultaneous quantitative evaluation of images, while the data acquisition with pulsed fields is run in the front-end. In order to test these aspects, DW velocity measurements in the widely studied Pt/Co/Pt system, which exhibits perpendicular magnetic anisotropy, are carried out at different temperatures (300 K). It is observed that the obtained features agree with the results reported in the literature, indicating the validity of the developed automation.

Properties Optimization of Soft Magnetic Composites Based on the Amorphous Powders with Double Layer Inorganic Coating by Phosphating and Sodium Silicate Treatment

Core-shell structured amorphous FeSiBCr@phosphate/silica powders were prepared by phosphating and sodium silicate treatment. The soft magnetic composites (SMCs) were fabricated based on these powders. The effects of phosphoric acid (H3PO4) concentration and annealing temperature on their properties were investigated. During the phosphating process, the powder coated with a low concentration of H3PO4-ethanol solution leads to uneven phosphate coating, while the peeling of phosphate coating occurs for the high H3PO4 concentration. Using 0.5 wt.% phosphoric solution, a uniform and dense insulation layer can be formed on the surface of the powder, resulting in increased resistivity and the reduced eddy current loss of the amorphous soft magnetic composites (ASMCs). This insulation layer can increase the roughness of the powder surface, which is beneficial to the subsequent coating of sodium silicate. By optimizing sodium silicate treatment, a complete and uniform SiO2 layer can be formed on the phosphated powders well, leading to double layer core-shell structure and excellent soft magnetic properties. The magnetic properties of amorphous SMCs can be further improved by post annealing due to the effectively released residual stress. The enhanced permeability and greatly reduced core loss can be achieved by annealing at 773 K, but the deterioration of magnetic properties occurs as the annealing temperature over 798 K, mainly due to the increase of α-Fe(Si) and Fe3B phases, which hinder the domain wall displacement and magnetic moment rotation. The excellent soft magnetic properties with permeability μe = 35 and core loss Ps = 368 kW/m3 at 50 mT/200 kHz have been obtained when the SMCs prepared with the powders coated by 0.5 wt.% H3PO4 and 2 wt.% sodium silicate were annealed at 773 K.

High density Fe-based soft magnetic composites with nice magnetic properties prepared by warm compaction

The influences of compacting temperature (Tc), molding pressure (Pm), contents of lubricant (Cl) and binder (Cb) on the compacted density (ρc) and its comprehensive soft magnetic properties for the FeSiCr soft magnetic composites (SMCs) fabricated by warm compaction were systematically studied. Appropriate increase of Tc is beneficial to improve the surface lubrication effect of magnetic powders during the forming process of SMCs, thus giving rise to the increase of ρc and the decrease of porosity fraction for the SMCs. Under this situation, the resistance of domain rotation and domain wall displacement in the SMCs during magnetization process is reduced, which is finally in favor of the improvement of SMCs’s soft magnetic properties. The results of loss separation show that the Ph value plays a dominant role in the variation trend of Pcv value for the FeSiCr-SMCs in the test frequency range of 20–200 KHz, wherein the ratio of Ph/Pcv is large than 81 %. Under the optimized process parameters of Tc= 110 ℃, Pm= 600 MPa, Cl= 1.5 wt. % and Cb = 2.5 wt. %, the ρc of FeSiCr-SMCs increases by 8.14 % to 6.38 kg/m3, and the SMCs exhibit better comprehensive soft magnetic properties compared with those at Tc = 25 ℃. Hereinto, μe increases by 19.89 % to 45.8 @ 100 kHz, Pcv decreases by 26.11 % to 495.8 kW/m3@f= 100 kHz, Bm= 50mT, and μe % reached 85.5 % at H = 8000 A/m. These results indicated that the warm compaction process is one of the effective ways to further promote Fe-based SMCs to meet the development requirements of high-frequency, miniaturization and high-power of electronic equipment.

Hysteresis loss free soft magnetic ferrites based on Larmor precession

Abstract A big enough transverse magnetic field applied in soft magnetic ferrite toroid can magnetize the ferrite to saturation in transverse direction and almost completely suppresses magnetic domain structures in the ferrite, the response to the longitudinal alternating electromagnetic field changes from the original domain wall displacements and spin rotations to the precession of magnetization around the transverse field and the hysteresis loss disappears in the ferrites. Both theoretical and experimental results indicate that the permeability and magnetic losses in the ferrite can be tuned by adjusting the transverse magnetic field. A higher Q value with relatively lower permeability can be achieved by increasing the transverse field, which ensures the ferrite can be operated at high frequencies with very low magnetic losses.