High Coercive Force Research Articles

Production of High-Coercive nanostructured Nd-Fe-B alloy by chemical method

For the first time, a nanostructured alloy powder with high coercive force was obtained by a chemical method without the addition of Dy, which can compete with physical methods of production. The work carried out a study of the influence of stoichiometric composition on the magnetic properties of nanostructured Nd-Fe-B alloys. Alloys with different contents of Nd, Fe, and B were synthesized: Nd12Fe84B6, Nd14Fe80B6, Nd16Fe76B8, and Nd16Fe72B8. With a decrease in the iron content in the first two compositions, a decrease in the iron content in the soft magnetic phase α-Fe was observed, which led to an increase in the coercive force Hc and a decrease in the values of Ms and Mr. Experiments have shown that an increase in the content of Nd and B promotes the formation of the hard magnetic phase Nd2Fe14B and an increase in the coercive force. For example, the nanostructured Nd16Fe76B8 alloy demonstrated a maximum coercive force of Hc = 8439 Oe, while compensating for the values of Ms (109 emu*g−1) and Mr (78 emu*g−1). A comprehensive study of the nanostructured Nd16Fe76B8 alloy was carried out, including structural analysis. XRD using FullProff and Vesta software revealed the tetragonal crystal structure of the Nd2Fe14B phase, providing details of the atomic arrangement. The unit cell contains four layers with Nd and Fe atoms, and boron atoms are embedded in the center of the octahedron of Nd and Fe atoms, playing an important role in the magnetic exchange interaction. The results of Mössbauer spectroscopy confirmed the presence of the Nd2Fe14B phase and revealed details of the state of Fe atoms in the structure of six sextets.

Investigation of the over-load unintentional remagnetization effect in series hybrid magnet variable flux memory machine

Variable flux memory machines (VFMMs) have become a research hotspot due to their adjustable air-gap flux with the employment of low coercive force (LCF) permanent magnets (PMs). Series hybrid magnet VFMMs (SHM-VFMMs) utilizing series-magnetic-circuit high coercive force (HCF) and LCF PMs are extensively investigated due to their excellent unintentional demagnetization (UD) withstand capability. Nevertheless, the existing researches still focus on the UD of LCF PMs under heavy load operation, and the remagnetization issue remains unreported. Therefore, in this paper, the over-load unintentional remagnetization (UR) effect of the a dual-layer-SHM-VFMM (DLSHM-VFMM) is first revealed, and its mechanism is investigated and analyzed in depth based on finite element (FE) analyses. A DLSHM-VFMM prototype is manufactured and tested to verify the effectiveness of the theoretical analyses.

Optimization Design of Surface-mounted Permanent Magnet Synchronous Motors Using Genetic Algorithms

The permanent magnet synchronous motor (PMSM) has gained widespread popularity in various industrial applications due to its simple structure, reliable performance, compact size, high efficiency, and adaptability to different shapes and sizes. Its exceptional characteristics have made it a focal point in industrial settings. The PMSM can be categorized into two primary types based on the arrangement of the permanent magnets (PM): interior permanent magnet (IPM) and surface-mounted permanent magnet (SPM). In the IPM, the magnets are embedded into the rotor, while in SPM, they are mounted on the rotor's surface. The utilization of PMs eliminates the need for excitation currents due to their high flux density and significant coercive force. This absence of excitation losses contributes to a notable increase in efficiency. In this study, a multi-objective optimal design approach is introduced for a surface mounted PMSM, aiming to achieve maximum efficiency while minimizing material costs. The optimization task is accomplished using a genetic algorithm. Furthermore, the motor designs are simulated using the finite element method (FEM) to assess and compare designs before and after the optimization process.

СИНТЕЗ ДИСПЕРСНЫХ ЖЕЛЕЗОСОДЕРЖАЩИХ ОКСИДНЫХ СИСТЕМ C ПРИМЕНЕНИЕМ ЭЛЕКТРОХИМИЧЕСКОГО РАСТВОРЕНИЯ УГЛЕРОДИСТОЙ СТАЛИ

Recovery and recycling of substandard metallic iron is a very urgent task from an environmental and economic point of view. At present increased attention is being paid to the problems of recycling metal waste, but relatively few methods of recycling have been developed. An electrochemical method is a promising approach, which makes it possible to obtain valuable products that are in demand by the industry. These are ferrites of alkaline earth metals, in particular, barium and strontium ferrites. Their valuable properties, for example, high coercive force, saturation magnetization, corrosion resistance and resistance to temperature changes, make them popular materials. In this regard, this study proposes a method of anodic oxidation of steel 3 in an aqueous saline solution, followed by the transition of the dissolution products into an electrolyte with the formation of a hydrated precipitate and its subsequent heat treatment. This method involves simple hardware design, environmental safety and low costs. This article discusses the features of anodic oxidation of steel 3 in aqueous salt solutions of barium and strontium compounds. It was revealed that activator ions, for example, chloride ions, which contribute metal oxidation, are necessary for the dissolution of steel in a nitrate solution. The results of high-temperature treatment of the resulting precipitate, in which the presence of two phases was established: strontium hexaferrite and iron III oxide. Thermal studies of dispersed precipitation at different temperature ranges demonstrate the presence of endothermic effects associated mainly with the removal of different forms of water.

Synthesis and investigation of mixed Zn–Ni spinel nanoparticles for microwave applications

Nickel ferrite solid solutions remain one of the main materials for a whole range of applications, including microwave equipment and components, the requirements for parameters and homogeneity of materials are constantly increasing. In this work, Ni1–xZnxFe2O4 nanoparticles with an average diameter of 12.5 nm were successfully synthesized by the microwave-assisted urea method. The temperature of a single-phase product formation was 400 °C, which is lower compared to more common precipitation from aqueous solution methods or solid-state route. Ni1–xZnxFe2O4 materials demonstrate high saturation magnetization and low coercive force. The magnetization changes with increasing Zn concentration and reaches the maximum at x = 0.5. Also, the increase in zinc content leads to an increase in the lattice parameters. The average size of ferrite nanoparticles synthesized by the microwave-assisted urea method is smaller compared to ferrites synthesized earlier by the co-precipitation method. Also, lower treatment temperatures provide higher stoichiometry, and homogeneity of materials while magnetization difference is negligible. These research results provide a general and effective route to synthesize other nanostructures for a variety of microwave components.

FeCo-BN magnetic composite membrane prepared via an atomized aerosol process for electromagnetic wave absorption and thermal management

Soft magnetic materials with high magnetic flux density and low coercive force exhibit a significant reflection loss, generating effective electromagnetic waves (EMWs) in the S-band to K-band frequency range. However, the limited complex permeabilities of commonly available soft magnetic materials at higher frequencies restrict their EMW absorption bandwidth. Here, we present a new class of thin EMW absorbing composite membrane comprising shape-modulated soft magnetic FeCo and thermally conductive boron nitride (BN) particles. The designed chemical process facilitates a one-step synthesis of composites with diverse structures, including spheres, cubes, and hollows, without requiring any shape-controlling additives. The FeCo/BN composite membrane, which was only 1.5 mm thick, demonstrated enhanced permeability and effective impedance matching, resulting in a high reflection loss value of − 46.4 dB at 11.3 GHz. Furthermore, the incorporation of BN nanoparticles with thermal conductivity enabled the thermal dissipation of the absorbed EMW energy. This study comprehensively investigated the correlation between shape modulation and complex permeability, which can provide valuable insights for the development of advanced EMW-absorbing materials.

Preparation of high-performance M-type strontium hexaferrites by ceramic method by optimizing the particle size of raw materials

High-performance strontium hexaferrites (SrM) was prepared by optimizing the particle size of strontium carbonate (SrCO3) and iron oxide (Fe2O3). The microstructure, morphology, particle size and magnetic properties of as-prepared strontium hexaferrite have been examined. The results showed that fine SrCO3 and Fe2O3 powders enhanced reactivity and lowered the starting temperature of the reaction. Magnetic result showed that as-prepared strontium hexaferrite with large saturation magnetization and high coercive force was fabricated by using fine SrCO3 and Fe2O3 powder. The optimum value of saturation magnetization (MS) and coercive force (HC) are 78.97emu/g and 5019Oe respectively. This study facilitated an energy-saving strategy for large-scale production of high-performance strontium hexaferrites in the future.

Investigation of Delta-Type Variable Flux Memory Machines Considering Magnetizing Current Limits

A simple delta-type interior-permanent magnet (PM) variable flux memory (VFM) machine exhibiting series-parallel magnetic coupling is investigated, and the limits of magnetizing current capacity are considered. The series-parallel coupled high coercive force (HCF) PMs and low coercive force (LCF) PMs integrate the merits of stable PM working point in series-type VFM machines with the high torque output in parallel-connected cases. Moreover, it is revealed that the iron bridges between the two kinds of the PMs play an essential role on magnetic coupling, de-/re-magnetization and torque capability. The VFM machines with wider iron bridges normally require higher magnetizing currents. The effects of the iron bridges are investigated based on the theoretical analysis and finite element methods. It is found that the narrower iron bridges contribute to the more significant series coupling and wider flux variation range, while the wider iron bridges sacrifice the flux variation but facilitate the torque improvement. A prototype machine is manufactured and the experiments are carried out to verify the investigations.

Analysis and Compensation of Hysteresis Effect on Electromagnetic Force in Axial Magnetic Bearings

Magnetic bearings (MBs) enable the rotor to run at high speed without lubrication due to no mechanical contact. However, the inherent hysteresis of ferromagnetic materials affects the support characteristics, reducing the design performance and stability margin of MBs, especially for axial MBs using materials with high coercive force. To analyze and compensate for the hysteresis effect on the electromagnetic force in axial MBs, an efficient method is proposed in this paper. Firstly, the hysteresis properties of the ferromagnetic materials are simulated by the Preisach model, and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> relationships under any external magnetic field can be determined. Taking into account the non-ideal factors such as hysteresis and saturation effects, the nonlinear magnetic circuit model of the axial MBs is established. The magnetic flux density working point under different control currents and eccentric displacements can be determined through iterative calculation, and then the air gap flux density distribution and electromagnetic force of the axial MBs are calculated. On this basis, the adverse effects of hysteresis on the bearing capacity and system stability of axial MBs are analyzed. A compensation algorithm is designed based on the inverse model to reduce the hysteresis effect. The inverse model is approximated modeled by the Lissajous curve. Finally, the proposed analysis and control methods are verified by the finite element method (FEM) or experiments. The results show that the proposed analysis method is capable of accomplishing good accuracy and requires less computation time than FEM, it can be applied to arbitrary current variation processes. In addition, the phase lag of the system is effectively improved with the compensation algorithm.

Analysis of flux barrier effect of LCF PM in series hybrid magnet variable flux memory machine

Variable flux memory machines (VFMMs) with series hybrid magnets using both low coercive force (LCF) and high coercive force (HCF) permanent magnets (PMs) have been recognized as a viable candidate for wide-speed-range industrial applications due to the advantages of high torque density and wide speed range. Nevertheless, the adverse effects of LCF PM on the HCF PM in series-type VFMM under different magnetization states (MSs) are still unreported. In this paper, the flux barrier effect (FBE) of the LCF PM existing in series hybrid magnet VFMM is first revealed, and its causes are discussed as well as analyzed in depth on the basis of the equivalent magnetic circuit method and finite-element (FE) analyses. A topology of VFMM with dual-layer PMs is further developed to alleviate the FBE induced from LCF PMs. It can be found that the FBE can be effectively suppressed by employing the dual-layer (DL) PM arrangement and additional leakage flux paths. A prototype of the proposed design is built, and the theoretical and FE results are experimentally verified.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Структура и магнитные свойства порошков сплавов (Sm,Zr)(Co,Fe,Cu)z для магнитопластов

The hard magnetic (Sm,Zr)(Co,Fe,Cu)z alloys intended for the application as powder filler in bonded magnets are considered. The microstructure and intrinsic coercive force of the Sm0.87Zr0.13(Co0.702Cu0.088Fe0.210)6.7, Sm0.81Zr0.19(Co0.702Cu0.088Fe0.210)6.3, and Sm0.85Zr0.15(Co0.690Cu0.070Fe0.240)6.8 alloys, the structural and magnetic states of which were prepared at different aging temperatures and cooling rates, are studied. The formation of the high coercive force and adequate squareness of the magnetic hysteresis loop for alloy powders under study was observed at grain and subgrain sizes of the 2:17 phase of 10 – 20 μm. It is shown that the anisotropic powders of the Sm0.87Zr0.13(Co0.702Cu0.088Fe0.210)6,7 alloy can be prepared for manufacturing bonded magnets with a coercive force of 14 – 20 kOe and higher, which are intended for the application in electric machines.

Design and Analysis of a Series-Type Permanent Magnet Axial Flux-Switching Memory Machine

This paper presents a new topology of an axial flux-switching memory machine with series-type permanent magnets (SPMs) to improve the flux regulation capability. The key idea was to combine low coercive force (LCF) PMs, which can be magnetized and demagnetized readily, with high coercive force (HCF) PMs in series to provide a variable air-gap magnetic flux. The flux regulating principle and the forward magnetization effect of HCF PMs on LCF PMs are presented and discussed. Based on 3D finite element analysis (FEA), the magnetization variation of LCF PMs and the electromagnetic performances of the machine under different magnetization states were investigated. Simulation results showed that the air-gap magnetic flux could be weakened by up to 45% by using a magnetization current impulse, significantly extending the PM motor’s flux-weakening speed range. Finally, a prototype machine was built, and experiments were performed to validate the predictions. The basic experimental validation shows that the measured back-EMF and the flux regulating characteristic matched the 3D FEA results well.

A Novel Slot PM-Assisted Hybrid Magnet Memory Machine

This article presents a novel slot permanent-magnet-assisted hybrid-magnet memory machine (SPMA-HMMM) with hybrid permanent magnets (PMs) in both stator yoke and slot opening. The key is each pair of yoke PMs is composed of one pole of high coercive force (HCF) PM and one pole of low coercive force (LCF) PM with flexible flux regulation. LCF PMs can be freely magnetized and demagnetized through dc current pulses, which are supplied by dc excitation coils wound on LCF PMs. This design leads to high efficiency of machine due to negligible field excitation loss. In this article, the machine configuration and operation principle are illustrated in detail. An equivalent magnetic circuit is modeled to unveil flux regulation and parallel excitation effect. Then, the electromagnetic performances of SPMA-HMMM under different magnetization states (MSs) are investigated, which verify flux regulation ability of the proposed machine with changeable MSs of LCF yoke PMs.

A Novel Asymmetric-PM Hybrid-Magnetic-Circuit Variable Flux Memory Machine for Traction Applications

In this paper, a novel asymmetric-permanent- magnet hybrid-magnetic-circuit variable flux memory machine (AH-VFMM) is proposed. The low coercive force (LCF) permanent magnets (PMs) are located on one biased side of the hybrid magnetic circuit branch, forming an AH configuration. Compared to its conventional symmetric-PM hybrid-magnetic-circuit (SH) counterpart, the proposed design benefits from the reduced usage of high coercive force (HCF) rare-earth magnet, alleviating the magnetic saturation to improve the flux regulation (FR) range, while the excellent load demagnetization withstand (LDW) capability can be still maintained. The topology evolution and operating principle of the proposed machine are introduced and described, respectively. Then, based on the combination of the magnetic equivalent circuit (MEC) method and Schwarz-Christoffel (SC) transformation, a hybrid analytical model is established to quantitatively reveal the mechanism of FR range extension, and facilitate the initial design of the machine. The electromagnetic characteristics of the proposed machine under different magnetization states (MSs) are investigated and compared with those of the conventional SH counterpart. Finally, an AH-VFMM prototype is manufactured, and the experimental measurements are carried out to verify the validity of the proposed design.

Structural and magnetic properties of Ho-doped CuFe2O4 nanoparticles prepared by a simple co-precipitation method

Nanocrystalline copper (II) ferrite with a spinel structure doped with holmium was synthesized by co-precipitation using an aqueous solution of NaOH as a precipitant and subsequent annealing at 800°C for 60 min. The doping limit was determined by X-ray phase analysis. The similarity of the real and nominal compositions of the doped samples was established by energy-dispersive X-ray spectroscopy using a scanning electron microscope. The obtained particles had an approximately spherical shape, and their size was 40–70 nm (X-ray phase analysis, transmission electron microscopy). The introduction of Ho3+ cations to х = 0.15 into a CuFe2O4 spinel lattice led to a decrease in the average size of crystallites, an increase inthe coercive force of nanopowders, and a decrease in excess magnetization and saturation magnetization. Synthesized CuFe2-xHoxO4 (х = 0, 0.1 and 0.15) nanopowders were magnetically hard materials with high coercive force.

Magnetic evaluation of accelerated aging degradation on 2.25Cr-1Mo steel with martensitic and bainitic microstructure

Accelerated aging-induced microstructure, mechanical properties, and magnetic properties were evaluated on martensitic and bainitic 2.25Cr-1Mo steel to correlate the properties for magnetic non-destructive evaluation (NDE) of aged Cr-Mo steel components. Decline in hardness and coercive force was observed with the increase in aging time for the microstructural modifications as the pinning of dislocations and magnetic domain wall corresponds to the mechanical and magnetic hardening. Although high hardness and coercive force was found for the martensitic steel compared to the bainitic steel due to its metastable microstructure with large amount of compressive residual stress, in longer periods of ageing the hardness and coercive force was found to be lower for the martensitic steel for its faster degradation. Strong correlations were found among the coercive force and microhardness in both the martensitic and bainitic steels, indicating a possibility of precise NDE of ageing degradation in Cr-Mo steel components by magnetic hysteresis loop measurement through a portable magnetic NDE device.

Boost the Crystal Installation and Magnetic Features of Cobalt Ferrite/M-Type Strontium Ferrite Nanocomposites Double Substituted by La3+ and Sm3+ Ions (2CoFe2O4/SrFe12-2xSmxLaxO19).

Spinel cobalt ferrite/hexagonal strontium hexaferrite (2CoFe2O4/SrFe12−2xSmxLaxO19; x = 0.2, 0.5, 1.0, 1.5) nanocomposites were fabricated using the tartaric acid precursor pathway, and the effects of La3+–Sm3+ double substitution on the formation, structure, and magnetic properties of CoFe2O4/SrFe12−2xSmxLaxO19 nanocomposite at different annealing temperatures were assayed through X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. A pure 2CoFe2O4/SrFe12O19 nanocomposite was obtained from the tartrate precursor complex annealed at 1100 °C for 2 h. The substitution of Fe3+ ion by Sm3–+La3+ions promoted the formation of pure 2CoFe2O4/SrFe12O19 nanocomposite at 1100 °C. The positions and intensities of the strongest peaks of hexagonal ferrite changed after Sm3+–La3+ substitution at ≤1100 °C. In addition, samples with an Sm3+–La3+ ratio of ≥1.0 annealed at 1200 °C for 2 h showed diffraction peaks for lanthanum cobalt oxide (La3Co3O8; dominant phase) and samarium ferrite (SmFeO3). The crystallite size range at all constituent phases was in the nanocrystalline range, from 39.4 nm to 122.4 nm. The average crystallite size of SrFe12O19 phase increased with the number of Sm3+–La3+ substitutions, whereas that of CoFe2O4 phase decreased with an x of up to 0.5. La–Sm co-doped ion substitution increased the saturation magnetization (Ms) value and the subrogated ratio to 0.2, and the Ms value decreased with the increasing number of double substitutions. A high saturation magnetization value (Ms = 69.6 emu/g) was obtained using a La3+–Sm3+ co-doped ratio of 0.2 at 1200 for 2 h, and a high coercive force value (Hc = 1192.0 Oe) was acquired using the same ratio at 1000 °C.

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: III. Matrix and Phases of the High-Coercivity State.

Observations of the surface domain structure (Kerr-effect), optical metallography, scanning electron microscopy (SEM-SE), and electron microprobe analysis (EPMA-SEM), measurements of major and minor magnetic hysteretic loops were used to study pseudo-single-crystal samples of (Sm,Zr)(Co,Cu,Fe)z alloys subjected to heat treatments to the high-coercivity state, which are used in fabricating sintered permanent magnets. Correlations between the chemical composition, hysteretic properties, structural components, domain structure, and phase state were determined for the concentration ranges that ensure wide variations of 4f-/4d-/3d-element ratio in the studied samples. The phase state formed by collinear and coherent phase components determines the high coercive force and ultimate magnetic hysteresis loops of the pseudo-single crystals. It was found that the 1:5 phase with the hexagonal structure (P6/mmm) is the matrix of the alloys for (Sm,Zr)(Co,Cu,Fe)z permanent magnets; the matrix undergoes phase transformations in the course of all heat treatments for the high-coercivity state. The heterogeneity observed with optical magnifications, namely, the observation of main structural components A and B, is due to the alternation, within the common matrix, of regions with modulated quasi-spherical precipitates and regions with hexagonal bipyramids (cellular phase) although, traditionally, many investigators consider the cellular phase as the matrix. It is shown that the relationship of volume fractions of structural components A and B that account for more than 0.9 volume fraction of the total, which is due to the integral chemical composition of the alloys, determines the main hysteretic performances of the samples. The Zr-rich phases, such as 5:19, 2:7, and 6:23, and a structural component with the variable stoichiometry (Sm(Co,Cu,Fe)3.5–5) that is almost free of Zr and contains up to 33 at% Cu, were found only within structural component A in quantities sufficient for EPMA analysis.