Magnetization Process Research Articles

Ion irradiation modulated magnetic properties of materials and its applications

Ion irradiation, a technology in which ion beams are used to irradiate materials, has high manipulation precision, short processing time, and many applications in the fields of material modification, chip manufacturing, biomedicine, energy and chemicals. Especially in magnetic material modification, customized modifications of magnetic materials can be achieved by precisely controlling the energy, dose, and direction of the ion beam. To further enhance the performances of magnetic materials and explore new magnetic devices, this study focuses on how ion irradiation precisely modulates various magnetic interactions and the analysis of its influence on the spin Hall effect and magnetic structural dynamics. Firstly, the latest research achievements are emphasized of ion irradiation regulated magnetic characteristics such as perpendicular magnetic anisotropy, exchange bias, and RKKY interaction. These regulation methods are crucial for understanding and optimizing the microstructure and properties of magnetic materials. Secondly, the significant role played by ion irradiation in regulating spin-orbit torque devices is discussed in detail. These applications demonstrate the potential of ion irradiation technology in designing high-performance magnetic storage and processing devices. Finally, the future applications of ion irradiation technology in the preparation of multifunctional magnetic sensors and magnetic media for information storage are discussed, highlighting its great enormous innovation and application potential in the field of magnetic materials.

Efficiency Assessment of Air Channel Cooling of a Multi-Turn Coil for Magnetic Pulse Processing of Metals

Efficiency Assessment of Air Channel Cooling of a Multi-Turn Coil for Magnetic Pulse Processing of Metals

Co-encapsulation of organic polymers and inorganic superparamagnetic iron oxide colloidal crystals requires matched diffusion time scales.

Nanoparticles (NPs) that contain both organic molecules and inorganic metal or metal oxide colloids in the same NP core are "composite nanoparticles" which are of interest in many applications, particularly in biomedicine as "theranostics" for the combined delivery of colloidal diagnostic imaging agents with therapeutic drugs. The rapid precipitation technique Flash NanoPrecipitation (FNP) enables continuous and scalable production of composite nanoparticles with hydrodynamic diameters between 40-200 nanometers (nm) that contain hydrophobic superparamagnetic iron oxide primary colloids. Composite NPs co-encapsulate these primary colloids (diameters of 6 nm, 15 nm, or 29 nm), a fluorescent dye (600 Daltons), and poly(styrene) homopolymer (1800, 50 000, or 200 000 Daltons) with NPs stabilized by a poly(styrene)-block-poly(ethylene glycol) (1600 Da-b-5000 Da) block copolymer. Nanoparticle assembly in FNP occurs by diffusion limited aggregation of the hydrophobic core components followed by adsorption of the hydrophobic block of the stabilizing polymer. The hydrodynamic diameter mismatch between the collapsed organic species and the primary colloids (0.5-5 nm versus 6-29 nm) creates a diffusion-aggregation time scale mismatch between components that can lead to nonstoichiometric co-encapsulation in the final nanoparticles; some nanoparticles are composites with primary colloids co-encapsulated alongside organics while others are devoid of the primary colloids and contain only organic species. We use a magnetic capture process to separate magnetic composite nanoparticles from organic-only nanoparticles and quantify the amount of iron oxide colloids and hydrophobic fluorescent dye (as a proxy for total hydrophobic polymer content) in the magnetic and nonmagnetic fractions of each formulation. Analysis of the microstructure in over 1100 individual nanoparticles by TEM imaging and composition measurements identifies the conditions that produce nonstoichiometric composite NP populations without co-encapsulated magnetic iron oxide colloids. Stoichiometric magnetically responsive composite NPs are produced when the ratio of characteristic diffusion-aggregation time scales between the inorganic primary colloid and the organic core component is less than 30 and all NPs in a dispersion contain organic and inorganic species in approximately the same ratio. These rules for assembly of colloids and organic components into homogeneous composite nanoparticles are broadly applicable.

Development and experimentation of free-form magnetic abrasive finishing process for the application of bearing surfaces

Development and experimentation of free-form magnetic abrasive finishing process for the application of bearing surfaces

Development and experimentation of Free-form Magnetic abrasive finishing process for the application of bearing surfaces

Development and experimentation of Free-form Magnetic abrasive finishing process for the application of bearing surfaces

The effect of Nd content on the elemental interdiffusion mechanism of Nd–Dy–Fe–B magnets

In this work, the effect of Nd content on the interdiffusion mechanism of Nd/Dy elements in Nd-Dy-Fe-B magnets was elucidated by studying the differences in the magnetic properties, microstructure, and demagnetization process. As the Nd content increased, a uniform, continuous, and thicker layer of rare earth-rich (RE-rich) phase formed inside the magnets, which had a good magnetic isolation effect. During the demagnetization process, the strong ferromagnetic coupling effect between the main phase grains could be effectively weakened. At the same time, the thicker RE-rich phase layer could lead to a more obvious interdiffusion phenomenon of Nd/Dy elements, forming more (Nd, Dy)2Fe14B phases with high magnetocrystalline anisotropy fields, resulting in higher coercivity of the magnets. This paper elucidated the influence of Nd content on the interdiffusion mechanism of dual alloy Nd-Dy-Fe-B magnets, which had important significance for the preparation of high-performance Nd-Dy-Fe-B magnets.

Q-axis Current Reverse Control of Variable Flux Memory Machines With High Salient Ratio During Magnetization Process for Speed Fluctuation Reduction

For variable flux memory machine (VFMM) with high salient ratio, a negative torque occurs when applying a positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_d</i> ) pulse to magnetize the machine under positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> ), causing a large speed drop. Since traditional speed controllers tend to increase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> at this point to increase the speed, unfortunately the higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> will generate stronger negative torque and further exacerbate the speed drop. To deal with this unique problem, a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current reverse control (QCRC) concept is proposed to achieve non-negative torque by reversing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> current during the period of negative torque occurrence. Specifically, based on QCRC concept, three control methods are newly designed, including look-up-table-based QCRC method (Method I), disturbance observer assistance + Method I (Method II) and disturbance-observer-based QCRC method (Method III). A super-twisting sliding mode torque observer (STSMTO) is newly structured as the disturbance observer. Furthermore, a linear active-disturbance-rejection-based feedforward decoupling (LADR-FFD) current controller is utilized to improve the current tracking performance, and the effect of its intrinsic time delay is also investigated. Finally, the effectiveness and feasibility of the proposed three control methods are validated through experimental measurement on a separated series-parallel VFMM (SSP-VFMM).

Magnetization process of antiferromagnetic quantum spin chains with the biquadratic exchange interaction

The magnetization processes of the S = 3/2 and S = 2 antiferromagnetic chains with the biquadratic interaction are investigated using the numerical diagonalization of the finite-size cluster. It is found that the system does not exhibit the spin nematic phase, which was predicted to occur for the S = 1 antiferromagnetic chain. Instead, the present analysis reveals that the quantum spin triatic and quatic liquid phases appear below the saturation magnetization for sufficiently large negative biquadratic interaction, for S = 3/2 and S = 2 chains, respectively. In addition it is also found that the magnetization jump up to the saturation magnetization appears for the small negative biquadratic interaction. The phase diagrams with respect to the negative biquadratic interaction and the magnetization are presented for the S = 3/2 and S = 2 antiferromagnetic chains.

Numerical simulation of bulk superconductor during pulsed field magnetization based on multi-field coupled analysis

High-temperature bulk superconductors are widely used in various superconducting devices due to their high critical current density, which enables them to trap high magnetic fields. However, the critical current density of bulk superconductors is influenced by magnetic field, temperature and stress, and both increase of stress and temperature can lead to a decrease in the critical current density. And the influence of magnetic field, current, stress are interactional. In this paper, the multi-field coupled analysis is employed to investigate the electromagnetic and mechanical behavior on bulk superconductor during pulsed field magnetization. The simulation results were compared with the present experimental results. The results showed a good agreement between the simulation and experimental results, further validating the reliability of the numerical simulation method. The magnetic field, current, temperature, and stress distribution and variation within the bulk sample during the pulsed magnetization process were calculated and analyzed. Additionally, the influence of the central crack and edge crack in the bulk superconductor was investigated. The results indicate that the region near the crack experiences a variation in current flow direction, resulting in local temperature rise and significant electromagnetic forces. The tip of the crack exhibits stress concentration, leading to a decrease in critical current density. Bulk supercondutor with edge crack case exhibits greater stress concentration compared to those with central crack case. The impact of crack length on maximum stress was analyzed, revealing that as the crack length increases, both the maximum hoop stress and radial stress within the bulk sample rise.

The comprehensive review of practical approaches of woe separation based on magnetic impact

The article presents an analytical review of magnetic oil treatment, which is an innovative method for preventing complications such as wax deposits and high viscosity of oil. It is concluded that the magnetic treatment of oil is associated with a change in the electrospin state and the evolution of radical pairs of asphaltenes, which are complex with ferromagnetic particles. This leads to an increase in intrinsic magnetic moments, structural rearrangement of supramolecular asphaltene structures and a change in the rheological parameters of oil. The destruction of the «armor shell» occurs due to the influence of the magnetic field on these complexes, which leads to the prevention of the formation of wax and salt deposits and the acceleration of water coagulation processes. The factors of effective magnetic treatment are oils with a high content of iron compounds, salt ions. The effective parameters of magnetic processing are generalized: high values of magnetic induction (up to 1 T), pulse repetition frequency from 5 to 30 Hz. The main advantages and disadvantages of permanent and alternating magnetic field devices are analyzed. A review of the results of industrial and laboratory studies on magnetic oil treatment is carried out. The maximum efficiency in reducing viscosity is 375%, reducing the deposition rate of paraffin is 87.5%, reducing the mass of wax deposits is 50%, reducing the corrosion rate is 45%. Keywords: magnetic treatment of crude oil; influence magnetic field on the oil; wax deposits; high-viscosity oil; heavy oil.

Wide-field imaging of the magnetization process in soft magnetic-thin film using diamond quantum sensors

The magnetization process of a soft magnetic CoFeB-SiO2 thin film was imaged using diamond quantum sensors with perfectly aligned nitrogen-vacancy centers along the [111] direction formed by CVD. Around the film edge, the easy and hard axes directions exhibited different responses to the external magnetic field, consistent with ones observed by magneto-optical Kerr effect microscopy. Moreover, quantum diamond imaging could observe discontinuous magnetization along domain walls as non-uniform magnetic charges (MCs). Quantum diamond imaging would help in visualization through MCs, such as irregularity in the material and relative orientation of magnetizations in neighboring domains.

BORIS – Micromagnetic, Spin Transport and Multiscale Atomistic Software for Modelling Magnetic Information Storage

A brief review of BORIS is given here, together with a review of recent works using this software, including applications to modelling magnetic hard-disk-drive read heads, ultrafast magnetization processes, computation of thermodynamic equilibrium states using Monte Carlo algorithms, and modelling skyrmions as information carriers. BORIS is a state-of-the-art multi-physics and multi-scale research software designed to solve three-dimensional magnetization dynamics problems, coupled with a self-consistent charge and spin transport solver, heat flow solver with temperature-dependent material parameters, and elastodynamics solver including thermoelastic and magnetoelastic/magnetostriction effects, in arbitrary multi-layered structures and shapes. Both micromagnetic and atomistic models are implemented, also allowing multi-scale modelling where computational spaces may be configured with multiple simultaneous micromagnetic and atomistic discretization regions. The software allows multi-GPU computations on any number of GPUs in parallel, in order to accelerate simulations and allow for larger problem sizes compared to single-GPU computations – this is the first magnetization dynamics software to allow multi-GPU computations, enabling large problems encompassing billions of cells to be simulated with unprecedented performance.

Determination of Changes in Flux Density of Transformer Steel Sheets

Magnetic fields in transformer cores are typically assumed to be one-dimensional fields, thus allowing magnetization processes to be regarded as axial magnetization. However, in the core corners or T-joint points of medium- and high-power rating transformers, the magnetic lines have different directions with respect to the rolling direction. This paper describes a method that allows changes in the flux density of transformer steel sheets to be calculated for any magnetization direction. These changes are assumed to depend only on certain limiting hysteresis loops assigned separately to the rolling and transverse directions of a tested transformer sheet, where these loops depend on the magnetization direction on the sheet plane. The selection of coefficients that define the limiting hysteresis loops for several magnetization directions is described, and the condition for the flux density saturation is considered. The resultant flux density in a specified magnetization direction is the geometric sum of the corresponding flux densities assigned to both the rolling and transverse directions. The limiting and partial hysteresis loops determined based on the proposed method for several magnetization directions are compared with analogous measured loops. Additionally, a comparison of the calculated hysteresis loops with loops showing changes in the resultant flux density for several magnetization direction is presented.

Influence of uniaxial tensile strain on magnetization behavior of Fe-9wt%Ni steel

This study investigated the effects of uniaxial tensile strain on the magnetization process of an Fe-9wt%Ni (9Ni) alloy to increase understanding of its magnetic behavior. As the applied strain was increased from 0 to 14 %, the magnetization curve changed remarkably, particularly under a high-intensity magnetic field, and magnetic flux density, relative permeability, remanence, and coercive force degraded significantly, especially at strains greater than the upper yield point. Increase in tensile strain caused increase in hysteresis losses, primarily because strain induced crystal defects, which affected the rearrangement of magnetic domains. Increased dislocation density was the primary contributor to the observed deterioration in magnetic properties; changes in texture and phase had little influence. This finding indicates that strain-induced deformation strongly affects the magnetic behavior of 9Ni alloys; this insight will be useful in research aimed at mitigating welding defects such as arc blow, that are attributed to the magnetization of Ni steel.

Compression cycling and magnetic response of single crystalline Ni-Mn-Ga particles/polymer composite: In-situ and ex-situ study

Ni-Mn-Ga particles/polymer composites are new magnetostrain active materials suitable for actuation and sensing. In the present work, we prepared mechanically anisotropic samples of the “30 vol% single crystalline Ni-Mn-Ga particles/silicone” composite material and systematically studied their cyclic stress-strain (S-S) evolutions along and perpendicular to the particle chains, while monitoring changes of magnetization curves. Four different compression cycling routes with the strain amplitude of 30% were explored. Magnetic measurements were served as the probes to indirectly detect microstructure changes of composite samples, whereas X-ray micro-CT images, alongside dimensions control of samples, were used for direct microstructural observations. The influences of the compression cycling routes on the parameters of S-S behaviors, such as an output stress, effective stiffness, and stress hysteresis, were revealed. It was found that the composite material after achieving equilibrium showed a rather good compression cycling stability of the mechanical and magnetic properties. It was revealed that composites being strongly deformed either along easy-magnetization axis (along the particle chains) or along hard-magnetization axis (perpendicularly to the particle chains) exhibited a magnetically harder behavior along the particle chains and magnetically easier behavior in the orthogonal direction, respectively. These unusual effects of a strong deformation of composite on its magnetization processes were discussed in terms of the particle rearrangements in the chains.

Magnetization coupled reverse osmosis (RO): Enhanced inhibition scaling mechanisms and operation optimization

In this study, magnetization pretreatment was applied to the reverse osmosis process. The scale inhibition effect and the mechanism of magnetization treatment were analyzed. The results show that after magnetization, the decay of water flux tended to slow down during RO and the flux recovery increased after cleaning. The Ryznar stability index of the solutions was calculated, which showed that magnetization could increase the solubility of carbonate solution and reduce the trend of carbonate scaling to a certain extent. The infrared spectra of the solutions showed that the hydrogen bonds of water molecules in the solution decreased after magnetization, indicating that the magnetization made the hydrogen bonds of water molecules break to form smaller clusters of water molecules, which might make the water molecules pass through the membrane more easily. After magnetization, the crystal size of the carbonate precipitated decreased and the sedimentation rate slowed down. Different flow rates and magnetization times were selected during the magnetization process. The results showed that when the flow velocity was greater than 0.24 m/s, the RSI, scale size and precipitation rate of the magnetized solution changed significantly compared with that of the unmagnetized solution. At the flow velocity of 0.48 m/s, the optimal magnetization time is 5 min. Moreover, the SEM characterization of the fouled membrane after filtration showed that after magnetization, the calcium carbonate deposited on the membrane surface appeared aragonite crystal, and the fouling was more loose, so it was easier to wash away during the membrane cleaning process.

Large room-temperature spontaneous exchange bias effect in LaFeO3 micro-polyhedrons

Single-phase materials with exchange bias (EB) effect at room temperature (RT) are very important for future applications in spintronic devices, magnetic storage, and sensors. To explore materials showing the EB effect at RT is an interesting and important issue. In this paper, LaFeO3 micro-polyhedrons composed of an average particle size of 66 nm nanoparticles have been synthesized by annealing LaFe(CN)6 precursors in air at 630 °C for 8 h. Magnetic hysteresis loops show that LaFeO3 micro-polyhedrons present a large spontaneous EB (SEB) effect (∼ 1.5 kOe) at RT after zero-field cooling (ZFC) and a gigant conventional EB (CEB) effect (∼ 5.6 kOe) after field cooling (FC) of 70 kOe. To the best of our knowledge, the current compound shows the largest negative EB field after ZFC at RT among SEB materials discovered so far. The successful fitting of training effect (TE) data with Binek’s model shows that the origin of SEB lies in the interface exchange coupling between different magnetic phases. The interface with the “pinning” effect of antiferromagnetic (AFM) matrix relative to ferromagnetic (FM) clusters exhibits unidirectional anisotropy, which is formed during the initial magnetization process. This interesting finding of the SEB effect at RT in single-phase perovskite LaFeO3 system may open a new direction for possible technological applications.

Energy Conversion by a Twisted Magnetic Structure at Magnetopause Boundary Layer: MMS Observations

AbstractThe Earth's magnetopause is an ion‐scale boundary that separates the magnetosphere from the shocked solar wind. At such boundary, energy‐conversion processes frequently occur. Previous studies suggested that such energy conversions are related to the magnetic reconnection process. Here, we report a new mechanism that the coaction between the twisted magnetic structure and lower‐hybrid waves can also drive energy conversion (J⋅ E, J is current density and E is electric field) at the magnetopause boundary layer, by using high‐resolution measurements of the four Magnetospheric Multiscale spacecraft. We find that such energy conversion is efficient (with magnitude up to 20 nW/m3) and is attributed to an intense current filament (j ≈ 3,800 nA/m2) and a fluctuating electric field driven by lower‐hybrid waves. With the help of the First‐Order Taylor Expansion method, we find that the intense current filament is driven by a twisted magnetic structure at electron scale. Our study improves the understanding of energy‐conversion processes at the Earth's magnetopause.

Enhanced soft-to-hard magnetic switching ratio in grain-oriented Fe–Si cores induced by helical anisotropy

The non-segmented shifted design of magnetic cores made of grain-oriented electrical steels, which induces the helical anisotropy, has been highly effective in reducing magnetic losses and minimizing acoustic noise in rotating machines. In order to address the challenges associated with precise theoretical modeling of complex underlying magnetization process, we have introduced angle-dependent first-order reversal curve diagrams. These diagrams offer significant insights into the microscopic properties of magnetization switching. By analyzing the distribution of coercive and interaction fields, we can identify distinct features that correspond to different domain wall processes and local coercivities, highlighting the magnetic behavior's heterogeneity. Through experimental measurements and theoretical analysis, we have gained quantitative understanding of the competing contributions from 90° and 180° domain wall processes in shifted structures. At shifting angles near the location of the hard magnetization axis, a notable transition in the magnetization process is observed by promoting the activation of the softer 180° domain wall processes. Among the different shifting angles tested, the structure with a shifting angle of 90° exhibits the highest ratio of soft-to-hard magnetization switching.

Control of the magnetic anisotropy and Curie temperature of monolayer 1T-CrTe2 for room temperature application

Magnetic units with large magnetic anisotropy energy (MAE) and high Curie temperature (Tc) are crucial for spintronic and quantum computing devices, which are a persisting demand for miniaturization of magnetic units. Using first-principles calculations and Monte Carlo simulation, it is found that monolayer 1T-CrTe2 exhibits strong perpendicular magnetic anisotropy with a MAE of approximately 5.29 meV and high Tc of ∼136 K. Interestingly, we find that the MAE and Tc of monolayer 1T-CrTe2 are tunable through electron/hole doping, strain, and heterostructure engineering. The magnetic easy-axis can be adjusted from out of plane to in plane, which is mainly attributed to the coupling between Te atomic orbitals (px, py). Second-order perturbation theory reveals that the spin–orbit coupling interaction between the occupied px and unoccupied py orbitals in opposite spin channel near Fermi level gives rise to negative contribution of MAE. Moreover, Tc can be enhanced to ∼230 K through super–superexchange mechanism of heterostructure due to the electron hopping between t2g/eg orbitals of Cr4+ ions and e1/a1 orbitals of Fe2+ ions. Importantly, we find that Tc can be boosted above room temperature by applying moderate strain (6%), ascribing to significant enhancement of MAE and exchange coupling constant. The present work indicates that monolayer 1T-CrTe2-based two-dimensional materials are very promising for room temperature application in magnetic storage and information processing.