NdFeB Powder Research Articles

Systematic investigation and correction of the magnetic hysteresis obtained by vibrating sample magnetometry

This work focused on a systematic study of data corrections for the vibrating sample magnetometry (VSM) to obtain reliable magnetic properties of strong ferromagnets. We designed the systematic experiments by varying the length-to-radius ratio of VSM samples between 1-5 and provided the step-by-step corrections of two commercial NdFeB powder magnets with reported energy product ((BH)max ) of 6.0±0.5 and 12.7±0.5 MGOe. Without data corrections, the measured hysteresis loops yield the (BH)max between 47.3% and 62.6% of their reported values with improper values of saturation magnetization (Ms ), remnant magnetization (Mr ), and Mr/Ms ratio. To correct the measured VSM hysteresis loop, firstly, the paramagnetic-like slope of 0.0500–0.0735 G/Oe was subtracted until the flat at high fields was obtained. Then, up to 6% of magnetization value and demagnetizing factor (N) of 0.30-0.53 was applied to achieve similar hysteresis loops for all samples. The corrected (BH)max after all processes is around 86-95% of the reported value. Moreover, by examining the samples with different packing densities, it was found that the loose-packed samples exhibit hysteresis distortion, which could be caused by an unwanted magnetostatic interaction and degree of particle rotation of the powder.

Microstructure optimization and magnetic properties enhancement of hot pressed Nd-Fe-B magnets via grain boundary diffusion of NdCu powder

Microstructure modification of Nd-Fe-B magnets plays a key role in regulating magnetic properties. In this work, low melting point NdCu alloy was added to improve the coercivity of NdFeB ribbons, and then high coercivity nanocrystalline NdFeB magnets were prepared by hot pressing sintering (HPS). The result shows that the coercivity of NdFeB powders blending with 15 wt% Nd-Cu powders obtained a maximum increment, as high as 12.69 kOe. After HPS, the fully dense magnets with excellent magnetic properties are obtained. Microstructure analysis confirmed that the Nd-Cu alloy has diffused into the interior of hard magnetic grains along the grain boundary during heat treatment. The enrichment of Nd, Pr, and Cu in the grain boundary phase weakens the magnetism of the grain boundary phase and reduces the intergranular exchange coupling. This is the main reason for the coercivity enhancement. In addition, the diffusion of Nd70Cu30 can significantly improve the thermal stability of the magnets.

NdFeB Magnets with Well‐Pronounced Anisotropic Magnetic Properties Made by Electric Current‐Assisted Sintering

Electric current‐assisted sintering (ECAS) technologies are highly promising for processing of NdFeB magnets. Due to the combination of direct Joule heating and application of external load, even powders, whose particle size distribution and morphology are not optimum for conventional powder processing like melt‐spun powders or magnet scrap, can be easily sintered to high densities. A systematic study is done to demonstrate the potential of field‐assisted sintering technique/spark plasma sintering (FAST/SPS) and flash spark plasma sintering (flash SPS) for sintering of NdFeB powders. Melt‐spun, commercial NdFeB powder (Magnequench MQU‐F) is used as starting material. Its platelet‐like shape makes this powder extremely difficult to sinter by conventional methods. This study clearly reveals that especially in the case of flash SPS application of external pressure in combination with short cycle times enables to achieve well‐pronounced anisotropic magnetic properties without the need of subsequent upset forging. Optimized flash SPS parameters are applied to NdFeB magnet scrap with broad particle size distribution, demonstrating the general potential of ECAS technologies for recycling of waste magnet materials. Finally, the results are benchmarked with respect to established NdFeB processing technologies and electrodischarge sintering (EDS), another promising ECAS technology with very short cycling time.

Magnetic Properties of the Mn55Bi45/Nd2Fe14B Hybrid Magnetic Alloys

The (Mn55Bi45)100−x/(Nd2Fe14B)x hybrid magnetic alloys were prepared by the ball milling of the combined annealed Mn55Bi45 powders and Nd2Fe14B powders. The magnetic properties at room temperature and elevated temperature were investigated. It was found that the saturation magnetization and the coercivity at room temperature increased significantly with the increasing Nd2Fe14B content. The enhanced energy product of 10.8 MGOe and 11.5 MGOe were obtained in (Mn55Bi45)40/(Nd2Fe14B)60 and (Mn55Bi45)20/(Nd2Fe14B)80. At elevated temperatures (350 K), the coercivities of 16.6 kOe and 16.1 kOe were obtained with Nd2Fe14B content of 20 wt.% and 40 wt.%, which were higher than those at room temperature. The temperature coefficients of coercivity of (Mn55Bi45)80/(Nd2Fe14B)20 and (Mn55Bi45)60/(Nd2Fe14B)40 were calculated to be positive, owing to the coercivity temperature characteristics of MnBi alloy. Finally, the energy products remained 10.5 MGOe and 10.1 MGOe in (Mn55Bi45)40/(Nd2Fe14B)60 and (Mn55Bi45)20/(Nd2Fe14B)80 at 350 K, which exhibited potential for high temperature applications.

Effect of NdFeB particle size on the performance of 3D printed bonded magnets of polyamide‐based composites

AbstractAdditive manufacturing has been widely used in the field of bonded magnets manufacturing. However, there are some key issues to be faced in order to obtain bonded magnets (BMs) with high performance. In this study, four different particle sizes of flake NdFeB powder (volume‐weighted mean diameter [VMD] of 5.60 μm, 19.21 μm, 33.25 μm, and 66.69 μm) were obtained by vibratory sieving. Flexible filaments for 3D printing BMs were produced using polyamide‐6 (PA6) as the substrate, and the production process is reported in this paper. Characterization of the performance of the 3D‐printed BMs revealed that the BMs with VMD less than 10 μm have excellent mechanical strength, but the ductility of the magnets decreases with decreasing VMD of NdFeB powder. As the NdFeB VMD decreases, the coercivity of the sample decreases and the remanence increases. This study provides a reference for the selection of filler particle size for 3D printing BMs, which can be used to develop 3D‐printed BMs with excellent performance.

Magnetic properties and magnetization mechanism of anisotropic NdFeB/SmFeN hybrid bonded magnets prepared with different coercivity NdFeB powders

Anisotropic NdFeB/SmFeN hybrid bonded magnets were prepared by warm compaction process under an orientation magnetic field of 22 kOe, mixing with anisotropic SmFeN powders in different addition and HDDR–NdFeB powders in different coercivity. With the addition of 20 wt% SmFeN, the density and remanence of hybrid magnets increase from 5.58 g/cm3, 8.4 kGs to 6.02 g/cm3, 9.0 kGs, respectively. And as the addition amount of SmFeN powders varies from 20 wt% to 40 wt%, the maximum energy product changes less than 0.5 MGOe. In addition, the magnetization process and the interactions between two powders were studied. It is found that the magnetization process of anisotropic NdFeB powders shows distinction in different initial states. The addition of SmFeN powders promotes the rotation of NdFeB powders together with applied field, which is beneficial to the degree of alignment of NdFeB powders. Because of the micron-sized long range coupling effect, the coercivity of hybrid magnets decreases slowly with the increase of low coercivity SmFeN. Meanwhile, the magnetization process of hybrid magnets is different from pure magnets, it increases rapidly at low field and then slowly, next leads to rapidity again and achieves the saturation magnetization finally.

Investigation of Wafer-Level Fabricated Permanent Micromagnets for MEMS.

Monolithic integration of permanent micromagnets into MEMS structures offers many advantages in magnetic MEMS applications. A novel technique called PowderMEMS, based on the agglomeration of micron-sized powders by atomic layer deposition (ALD), has been used to fabricate permanent micromagnets on 8-inch wafers. In this paper, we report the fabrication and magnetic characterization of PowderMEMS micromagnets prepared from two different NdFeB powder particle sizes. A remanence of 423 mT and intrinsic coercivity of 924 mT is achieved at the low ALD process temperature of 75 °C, making this process compatible with MEMS technology. The magnetic reversible mechanism in the micromagnets is discussed with the help of the Wohlfarth equation. To ensure the operability of such integrated micromagnets in different application environments, we conducted a set of experiments to systematically investigate the thermal and corrosive stability. NdFeB micromagnets with larger powder particle size (d50 = 25 µm) exhibit high thermal stability in air. Furthermore, the corrosion stability of the micromagnets is significantly improved by an additional silicon oxide passivation layer deposited by plasma-enhanced chemical vapor deposition (PECVD). The presented results demonstrate the durability of PowderMEMS micromagnets, enabling their application in various fields, e.g., microfluidics, sensors, actuators, and microelectronics.

Nd2Fe14B/FeCo Core–Shell Nanoparticle Synthesis Using Galvanic Substitution Based Electroless Plating

Core–shell structured magnetic nanoparticles combine hard and soft phases to improve energy efficiency. The mutual interaction of the two phases can lead to the exchange spring effect, leading to higher magnetic energy. In this regard, synthesis of Nd2Fe14B-based core–shell-structured powders have proven to be elusive, due to the relatively reactive nature of this phase. In this study, a process has been established for successfully coating the surface of Nd2Fe14B powders with a FeCo layer using the galvanic displacement method. Initially, a binary phase magnetic powder was synthesized containing Nd2Fe14B and Nd2Fe17 phase. Subsequently, the powders were coated using a Co precursor at 303 K. During coating, the metastable Nd2Fe17 phase was dissolved, and the Fe ions were released into the solution. Subsequently, the Fe ions deposited together with the Co ions on the surface of Nd2Fe14B powder to form a FeCo shell. The deposited layer thickness and composition was confirmed using TEM analysis.

Selective laser melting of Nd-Fe-B: Single track study

Single tracks of Nd2Fe14B powder were obtained by selective laser melting with various process parameters. Initial powder material morphology and elemental composition were controlled. Single tracks were analyzed to study the material’s melting features under laser irradiation and determine optimal printing regimes. 950 mm/s scanning speed is a boundary between complete melting and sintering. Single tracks morphology and their cross-sections dimensions and shape were investigated. A selective laser melting process window with a linear energy density of 300–500 J/m with 150–200 W of laser powder and 300–700 mm/s scanning speed was optimal for proper continuous melting of single tracks.

A Review on Properties of Concrete with Magnetizing Cement

The incorporation of strong magnetic powders (NdFeB) into cement mixtures has produced improved mechanical properties of cement pastes. The magnetic cement (cementitious magnet) used a simple and inexpensive cement process to form complex forms of the NdFeB magnet. Particulate NdFeB has been distributed uniformly in the cement matrix. The magnetic cement composites increased in density and compressive strength with the NdFeB concentration. Magnetization (stable up to one year) also increased with NdFeB powder but there was no improvement in coercivity. The introduction of magnetic particles into cement matrices has also been another important method in recent years to enhance the mechanical and other properties of cement-based materials. Nanoparticles (IONs) made from iron oxide (Fe2O3, Fe2O4) are among the most popular cement fillers. Cement composites mixed with IONs showed enhanced compressive strength, as well as other enhanced functions. This paper presents literature analysis of a study of magnetizing cement on concrete properties.

Automated Filling of Dry Micron-Sized Particles into Micro Mold Pattern within Planar Substrates for the Fabrication of Powder-Based 3D Microstructures.

Powder-based techniques are gaining increasing interest for the fabrication of microstructures on planar substrates. A typical approach comprises the filling of a mold pattern with micron-sized particles of the desired material, and their fixation there. Commonly powder-loaded pastes or inks are filled into the molds. To meet the smallest dimensions and highest filling factors, the utilization of dry powder as the raw material is more beneficial. However, an appropriate automated technique for filling a micro mold pattern with dry micron-sized particles is missing up to now. This paper presents a corresponding approach based on the superimposition of high- and low-frequency oscillations for particle mobilization. Rubber balls are utilized to achieve dense packing. For verification, micromagnets are created from 5 µm NdFeB powder on 8” Si substrates, using the novel automated mold filling technique, as well as an existing manual one. Subsequent atomic layer deposition is utilized to agglomerate the loose NdFeB particles into rigid microstructures. The magnetic properties and inner structure of the NdFeB micromagnets are investigated. It is shown that the novel automated technique outperforms the manual one in major terms.

Nd-Fe-B: From sludge waste to powders via purification and modified Ca-reduction reaction process

The oil-based Nd-Fe-B sludge waste was directly recycled to single-phase Nd2Fe14B powders via the combination of purification and modified Ca-reduction reaction method. The impurities and organics in the purified Nd-Fe-B sludge waste were greatly reduced, reducing calcium consumption in the subsequent reduction and diffusion (RD) process, thereby reducing the cost. By further optimizing the Ca-reduction diffusion parameters, especially the mass ratio of CaCl2 and KCl, where the liquid CaCl2, along with the gaseous KCl provide conditions for sufficient and uniform Ca-reduction reaction, high-property Nd-Fe-B magnetic powders with good dispersion, uniform particle sizes, and excellent orientation, were successfully obtained. Using the mixed diffusion medium of CaCl2 and KCl with a mass ratio of 1:1, the room-temperature magnetization of the recycled Nd-Fe-B powders was increased to 157 emu/g at 3 T-magnetic field, which was about 28 % higher than that of the original sludge. The contents of carbon, hydrogen, and oxygen in the recycled magnetic powders were significantly reduced from 6.8, 1.8, and 5.9 wt% to 0.1, 0.19, and 0.56 wt%, respectively. In addition, the uniform grain size with X50 = 3.6 μm and good distribution greatly improved the orientation, which can be beneficial to the preparation of the bonded or sintered Nd-Fe-B-based magnets. The reasons that CaCl2-KCl mixed diffusion medium can lead to well-dispersed, uniform recycled powder with high magnetization arise from a combination of factors for improving the liquid phase reaction environment and the gaseous KCl to prevent agglomeration and inhibit particles merging or growth.

Effect of silane coupling agents on flowability and compressibility of compound for bonded NdFeB magnet

Based on the difference of the Y-terminal functional group of the silane coupling agent (Y–Si(X)3), four different silane coupling agents were employed to pretreat the surface of the NdFeB powders. The effects of silane coupling agents on the flowability and compressibility of compounds for preparing bonded NdFeB magnets were studied. It is indicated that compounds pretreated by silane coupling agents have weaker friction and meshing force. The apparent density is increased by 0.3 g/cm3 compared with the compound without silane coupling agent, and the radial crushing strength is significantly increased by about 3–4 times. In addition, the epoxy resin is more evenly distributed on the surface of the compounds treated by silane coupling agents observed by scanning electron microscopy, and some agglomerated particles are produced. Also, the compressibility of compounds with silane coupling agents is significantly improved due to the fact that hardening exponents are reduced. However, the addition of silane coupling agents has almost no effect on the magnetic properties of bonded magnets. The special energy was used to manifest the flowability of magnetic powder particles representing the macroscopic performance of the force between powder particles, providing a new direction for the study of the interface compatibility of two-phase or multiphase composite materials.

Coercivity enhancement of hot-deformed NdFeB permanent magnets with AlCuZn eutectic alloy grain boundary diffusion

It is approved that grain boundary diffusion is an effective method to increase the coercivity of hot-deformed NdFeB magnet. In this paper, a new rare earth-free grain boundary diffusion source of hot-deformed magnet was studied. AlCuZn powders blended with commercial NdFeB powders were hot-compacted to obtain fully dense magnets, hot-deformed into anisotropic magnets and finally annealed to gain better homogeneity. Initially, the influences of annealing temperature and time on the magnetic properties of the specimens were studied and the optimal parameters of 600 °C and 60 min were achieved. Then, by changing the proportions of AlCuZn grain boundary diffusion, the coercivity, remanence and maximum energy product of the hot-deformed NdFeB magnets were examined. The result showed that with 1.0 wt% AlCuZn grain boundary diffusion and annealing at 600 °C for 60 min, the coercivity rose from 828 to 987 kA·m−1 without deteriorating the remanence. Microstructural analysis confirmed that AlCuZn diffused into the intergranular boundaries and the magnet diffused with AlCuZn possessed finer grains than that of without AlCuZn grain boundary diffusion.

Selective Laser Sintering-Based 4D Printing of Magnetism-Responsive Grippers.

Components fabricated by four-dimensional (4D) printing hold the potential for applications in soft robotics because of their characteristics of responding to external stimuli. Grippers, being the common structures used in robotics, were fabricated by the selective laser sintering (SLS)-based 4D printing of magnetism-responsive materials and tested for remote-controllable deformation in an external magnetic field. A composite material consisting of magnetic Nd2Fe14B powder and thermoplastic polyurethane powder was selected as the raw material for the SLS; the magnetic particle acquired permanent magnetism by magnetization after the SLS process. Microscopic characterization showed the homogeneous dispersion of magnetic particles inside the polymer matrix. The magnetic induction intensity distribution was systematically investigated by both experiments and numerical simulations. The reliability of the numerical model proposed was justified by the excellent consistency between them. The deformation of the grippers could be regulated by tuning the magnetic particle content and the distance from the external magnet; the deformation mechanism is investigated numerically. The magnetic driving force and the corresponding horizontal displacement are calculated, thus having high accuracy compared with the existing research that obtained the deformation amount by only visual inspection. Mechanical properties of the SLS-fabricated magnetic polymer composite specimens were also studied because of their close relationship with the deformation behaviors. These findings provide guidance for future research on controllable deformation and driving force calculation for 4D printing.

Spin reorientation temperature of ultrafine and nanostructured Nd2Fe14B particles obtained by surfactant-assisted ball milling

Spin reorientation temperature (TSR) of sintered Nd2Fe14B ingots, hydrogenation-disproportionation-desorption-recombination (HDDR) processed Nd2Fe14B powder and surfactant-assisted ball-milled ultrafine nanostructured Nd2Fe14B particles has been determined. TSR value was found to decrease from 135 K for sintered Nd2Fe14B ingot to 129 K for HDDR processed Nd2Fe14B particles of 50-200 μm size composed of ∼300 nm grains. Interestingly, TSR value was increased after surfactant-assisted (SA) ball milling of HDDR powder reaching 134 K for 1-2 μm particles and 136 K for ∼300 nm isolated single-crystalline particles. Transformation of single-crystalline particles to polycrystalline flakes after intense SA-ball milling resulted in a decrease of the TSR to a value of 128 K. A detailed crystallographic, microstructural, and magnetic investigations have been performed and the possible reasons for the variation of TSR value have been discussed.

Effect of Molding Pressure on Structure and Properties of Ring-Shaped Bonded NdFeB Magnet

Ring-shaped polymer-bonded magnets (RSMs) were produced from a mixture of an isotropic NdFeB powder, steel use stainless (SUS) powder, and epoxy resins as binders, using a comprehension-molding technique. Morphology of RSM determined by an SEM indicated that inappropriate molding pressure leads surface defect and brings adverse impact on properties of magnets. The research on mechanical properties shows that the maximum tensile strength of 11.4 N was achieved at optimal pressing pressure of 85 kN. Meanwhile, RSM has excellent stability as the critical component of motor and its amount of unbalance is as low as 0.754 mg. Magnetic property in optimal mechanical conditions was also found to be optimum at H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> = 8.42 kA/m and (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 31.17 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Early Characterization of NdFeB and NdFeB /Co-Al Composites of Sintering Using SPS

The purpose of this study is to obtain a permanent magnet end-product from NdFeB and NdFeB / Co-Al composite material from SPS sintering which has high density with small grain size and strong corrosion resistance. NdFeB powder and NdFeB/Co-Al composites (0.2 and 0.5weight%) of several micron-sized particles resulting from the milling process have been successfully sintered with a temperature parameter of 800°C for 10 minutes and a pressure of 50MPa in dies with a diameter of 20 mm in a vacuum chamber. Optical micrographs show that the grains are uniformly and smoothly distributed throughout the surface. This is showing the types of grain distributions which has good mechanical properties. The X-ray analysis result shows the phase analysis confirms the presence of such main PM phases as Nd, Fe and B. From SEM observation, the particles have irregular shapes and a large particle size distribution. The density value of the sample is in the range of 7.1 - 7.3. From the density measurement it is also known that the sintering sample with SPS has a high-density level which is close to 100%, so it can be said that it has formed fully dense.

Interstitial nitrogen Atomic effect on the magnetic properties of Nd2Fe14B compound

The quaternary interstitial nitrides Nd2Fe14BNδ was synthesized through the gas-solid reaction of N2 gas and Nd2Fe14B powders. It was found that Nd2Fe14BNδ alloy maintains the tetragonal structure (space group P42/mnm) with an expansion of the unit cell. Structure analyses showed the nitrogen concentration (δ) is about 0.352(48) with the volume-expansion ratio (ΔV/V) of 0.6613% in the unit cell. Refinement of neutron diffraction data indicated that the N has a site occupation preference (8:3) for the 4e (0, 0, 0.0652) site over the 4f (0.1000, 0.1000, 0) site. The room temperature saturation magnetization and the magnetocrystalline anisotropy field of Nd2Fe14BNδ slightly decrease by about 6% and 5% as compared to the parent alloy, respectively. The Curie temperature of Nd2Fe14B compound increases from 312 °C to 331 °C after nitrogenation with such a subtle volume expansion, which provides a validation prediction that we may increase the volume-expansion ratio to improve Tc further. Therefore, Nd2Fe14BNδ, with better temperature stability could be obtained.

3D printing of high performance polymer-bonded PEEK-NdFeB magnetic composite materials

Permanent Rare Earth magnets are becoming more and more important in efficient motors and generators with high energy density. Among them NdFeB magnets are the most employed, with NdFeB having higher remanence, high coercivity and energy product. Nevertheless,their poor corrosion resistance makes them susceptible to degradation of the magnetic properties. One possible solution is the development of innovative polymeric composite magnetic materials. The preparation of NdFeB powders filled polymeric matrix (PEEK), with a double goal of protecting the magnetic alloy is proposed, thus preventing it from corrosion, and to realize a new material that can be shaped in the form of filaments. This material was used as feedstock in the 3D printing process to produce high performance magnets with customized and optimized design. The PEEK-NdFeB filaments were produced with three percentages of filler amount(i.e. 25, 50 and 75 wt%). PEEK neat filaments were produced as reference. The influence of the filler on the main thermomechanical properties of the resulting composites, as well as its effect onthe 3D printing process were evaluated by means of different investigation techniques (DSC, DMTA, XRD, tensile testing). The magnetic properties exhibited by Fused Filament Fabrication (FFF) printed parts confirmed the feasibility of employing such a combination of an innovative manufacturing technique and high-performance PEEK-NdFeB compounds.The characterization carried out on both neat and composite filaments evidenced that the presence of the filler slightly decreased the thermal stability, increased the elastic modulus while decreasing ductility and maximum tensile strength. By means of DSC analysis, it was confirmed that the crystallinity is influenced by the presence of the filler. Magnetic measurement performed on the 3D printed parts demonstrate that interesting magnetic properties were achieved, confirming the feasibility of the magnetic 3D printed composite with PEEK.