Rare-earth Magnets Research Articles

The influence of substrate orientation on the magnetic behavior of nearly-stoichiometric Mn5Ge3 thin films: DFT calculations and experimental analysis

The Mn5Ge3 exhibits a wide range of fascinating properties such as high spin polarization up to 42 %, large spin diffusion lengths, near-room Curie temperature, and possible integration with Ge, GaAs, and Si substrates. The influence of substrate orientation on magnetic behavior has been investigated. The thin films studied present an in-plane magnetic reversal which is isotropic in samples grown on GaAs(111) and anisotropic in samples grown on GaAs(001). Another difference observed is a linear trend to saturation on the out-of-plane hysteresis loop in samples grown on GaAs(111), comparatively to samples grown on GaAs(001). To better understand this scenario, Density Functional Theory (DFT) calculations were conducted. The results indicate a ferromagnetic metallic ground state with properties that are consistent with the experimental results. The projected densities of states indicate that the main responsible for the magnetic moment observed in the Mn5Ge3 is the Mn-Mn interaction. The magnetic field distribution isosurfaces obtained from the DFT calculations offer a satisfactory explanation of the magnetic reversal experimentally observed, especially the in-plane magnetic behavior in samples grown on both GaAs(111) and GaAs(001) substrates. This work provides a theoretical-experimental approach that allows a deeper understanding of the magnetic anisotropy behavior under the influence of the crystallographic orientation of the substrate observed in nearly-stoichiometric Mn5Ge3 thin films, which is a good candidate for rare-earth free magnet in spintronic applications.

Electromagnetic Design Optimization Integrated with Mechanical Stress Analysis of PM-Assisted Synchronous Reluctance Machine Topologies Enabled with a Blend of Magnets

Permanent Magnet-Assisted Synchronous Reluctance Machines (PMASynRM) provide a low-cost alternative to Surface PM Machines due to the use of relatively lower grades of rare-earth (RE) or RE-free magnets, as the performance degradation due to weaker magnets is compensated by the presence of reluctance torque. However, the weaker magnets suffer from a high risk of demagnetization, leading to unreliable motor operation. Using a blend of RE and RE-free magnets has the potential to overcome this issue. This paper proposes to blend different grades of various rare-earth (RE) and rare-earth-free (RE-free) magnets in six different combinations and utilizes them in two-layer and three-layer U-shaped PMASynRM topologies with both eight-pole and six-pole variations. The rotor of the various designs is then optimized using a differential evolution (DE) based optimization algorithm to obtain low-cost designs with reduced RE magnet volume and minimum demagnetization risk. The optimization of each design is also integrated with the evaluation of mechanical stresses in the rotor laminations so as to maintain the stresses below the material yield strength. Furthermore, the various performance metrics, such as toque–speed/power–speed characteristics, demagnetization, and efficiency maps, are evaluated for each of the optimized and mechanically feasible designs. A quantitative comparison of the various optimized designs is also obtained to highlight the various trade-offs. The results indicate the feasibility of meeting the baseline torque requirement across the entire speed range, even with a 100% reduction in RE magnet volume and less than 5% demagnetization risk, while achieving a cost reduction exceeding 50%. Moreover, the two-layer, eight-pole designs exhibit relatively higher performance, whereas the three-layer, eight-pole designs are found to be the most economical option.

Additive Manufacturing of Rare Earth Permanent Magnetic Materials: Research Status and Prospects

With the rapid development of intelligent manufacturing, modern components are accelerating toward being light weight, miniaturized, and complex, which provides a broad space for the application of rare earth permanent magnet materials. As an emerging near-net-shape manufacturing process, additive manufacturing (AM) has a short process flow and significantly reduces material loss and energy consumption, which brings new possibilities and impetus to the development of rare earth permanent magnetic materials. Here, the applications of AM technology in the field of rare earth permanent magnets in recent years are reviewed and prospected, including laser powder bed fusion (LPBF), fused deposition modeling (FDM), and binder jetting (BJ) techniques. Research has found that the magnetic properties of AM Nd-Fe-B magnets can reach or even exceed the traditional bonded magnets. In addition, in situ magnetic field alignment, in situ grain boundary infiltration, and post-processing methods are effective in enhancing the magnetic properties of AM magnets. These results have laid a good foundation for the development of AM rare earth permanent magnets.

From muck to magnets

James McKenzie looks at the work of University of Birmingham spin-off firm HyProMag, which has developed a technique for recycling rare-earth magnets.

Pt‐Fe loaded nanostructured silicon and improvement of the magnetic performance

AbstractThis work reports the pore‐filling of porous silicon (PSi) and the loading of silicon nanotubes (SiNTs) with Pt‐Fe nanoparticles (NPs) and the corresponding different magnetic behavior of the two composite systems. The fabrication of magnetic hard/soft nanostructures is in demand for the purpose of achieving both a high energy product as well as the replacement of rare earth permanent magnets. Pt‐Fe templated by PSi shows a higher coercivity and remanence than SiNTs/Pt‐Fe and thus a higher hard magnetic performance, the difference between coercivities being about 57%. Considering that the Pt‐Fe deposits employ different molar ratios of Pt to Fe the coercivities vary in a range of 5% in the case of both template types. Comparing Pt‐Fe loaded samples with Co‐loaded samples in all cases, an increase of the coercivity and the remanence is observed for Pt‐Fe, whereas in the case of PSi as template material the increase is significantly stronger (about twice as much) than in the case of SiNTs samples. Furthermore, the samples are investigated at high temperatures up to 950 K to determine the Curie temperature of the systems.

An in-situ magnetising holder achieving 1.5 T in-plane field in 200 kV transmission electron microscope

A strong in-plane magnetic field is required for Lorentz transmission electron microscopy (LTEM) to observe the evolution of the magnetic domain structure of materials with high coercivity, particularly for research on rare-earth permanent magnets. However, the maximum field of the present in-situ magnetising holder applied in 200-kV or 300-kV TEM does not exceed 0.1 T. In this study, the reason for the low field was analysed, and the field strength was significantly elevated by reducing the field application area of the field generator. From finite element method calculations and experimental measurements, a 1.5 T in-plane field was achieved by our new holder in a 200-kV TEM, and images with good quality could still be obtained. Using the newly developed holder, the magnetisation process of hot-pressed NdFeB magnets was observed. The in-situ magnetising holder can be used in research on a wide variety of magnetic materials.

Intrinsic magnetism and practical potential of 2:14:1-type magnet with rare earth supplied only by misch-metal

2:14:1-type rare earth (R) permanent magnet R2Fe14B, as a functional material, plays an indispensable role in transportation, machinery, energy and other fields. Under the pressure of resources, cost and environment, special attention has been devoted to magnets replaced by high-abundance rare earth. But until now, 2:14:1 phase containing only misch-metal (MM) is not considered suitable for practical production. In this work, from the perspective of intrinsic properties, it is confirmed for the first time that MM2Fe14B with MM (La, Ce and other high-abundance rare earth content as high as 80%) has the potential to become a permanent material. The saturation magnetization Ms at 300 K is 27.36 μB/f.u, and the anisotropy parameters are μ0Ha = 4.2 T, K1 = 1.39 MJ/m3 and K2 = 0.42 MJ/m3. We noted that the temperature dependence of Ms, K1 and K2 are very similar to Nd2Fe14B. Curie temperature TC and spin reorientation temperature Tsr of MM2Fe14B are 488 K and 74 K, respectively. When the temperature is lower than Tsr, the anisotropy changes from easy-uniaxial to easy-cone. The spin reorientation angle θs is about 18° at 4.2 K, less than Nd2Fe14B. Small θs means that strong uniaxial anisotropy can be maintained, which is important to achieve high-performance. Micromagnetic simulation was also introduced to confirm the effect of θs and grain boundary on MM-Fe-B performance. The intrinsic magnetism not only provides strong evidence for the practicability of MM-Fe-B, but also of great significance for further study on the mechanism of rare earth magnets with high-performance and high-abundance.

Vector hysteresis loops of rare earth magnets measured in a biaxial vibrating sample magnetometer

Vector hysteresis loops of rare earth magnets measured in a biaxial vibrating sample magnetometer

Comparing forceps and self-assembled intraocular rare earth magnet in removing metallic intraocular foreign bodies in 25-guage vitrectomy

PurposeTo compare the efficacy and efficiency of self-assembled intraocular rare earth magnet and forceps in removing intraocular foreign bodies(IOFBs) undergoing 25-gauge(G) pars plana vitrectomy.MethodsA total of 30 patients with metallic IOFB underwent 25-G PPV were enrolled into this study. Self-assembled intraocular rare earth magnet were used in 15 patients(bar group), and forceps were used in 15 patients(forceps group). Success rate of removing IOFB, time taken to remove IOFB, incidence of IOFB slippage and fall, iatrogenic retinal damages were compared between the two groups.ResultsThere was no significant difference in success rate of removing IOFBs between the groups(93.3% and 100%, P > 0.99). The median time taken of removing FB was significantly shorter in bar group than in forceps group(112 and 295 s, P = 0.001). None of the patients in bar group had IOFB slippage and fall, or related iatrogenic retinal damage in the process of removal. In forceps group, IOFB slippage and fall during removal were observed in 7 of 15(47.6%) patients, related iatrogenic retinal injuries were recorded in 6 of 15(40.0%) patients, both were significantly higher than bar group(P = 0.003 and P = 0.017, respectively).ConclusionsCompared with forceps, the assembled intraocular magnet can greatly reduce the possibility of IOFB slippage and fall, prevent related iatrogenic retinal damage, and shorten the time taken to remove IOFB. The assembled intraocular magnet can be an useful tool in removing metallic IOFBs in PPV.

Optimal Design of a Novel Consequent-Pole Interior Permanent Magnet Motor with Flared-Structured Rotor

Interior permanent magnet motors are widely used in applications requiring high power density and high efficiency due to their high torque-generating capabilities. Recently, given the price fluctuations and unstable supply of rare earth permanent magnets, alternative configurations with reduced use of permanent magnets are being sought. Among the various candidates related to this, the consequent-pole type rotor structure can halve the number of permanent magnets used compared with conventional structures. However, in a no-load analysis, the waveform of the back electromotive force becomes asymmetric, generating a harmonic component. As a result, there is a disadvantage that the torque ripple increases. To overcome these shortcomings, we propose a novel rotor structure that applies a consequent-pole structure to an embedded permanent-magnet motor structure, wherein a number of permanent magnets are arranged in a flared structure to constitute a single polarity. In the proposed flared-structured magnet arrangement, it is possible to adjust the angle of the permanent magnet and the polar angle to mitigate the asymmetry of the back-EMF waveform. The proposed structure was optimized with a genetic algorithm and a prototype of the optimal model was constructed and experimentally evaluated to verify its validity. Finally, the performance improvement and validity of the proposed structure were verified by comparing the analysis results of the optimal model with the experimental results.

Fe-Ni based alloys as rare-earth free gap permanent magnets

L10-ordered FeNi phase has potential as a rare-earth free permanent magnet due to its large magnetization and high Curie temperature. However, low long-range crystal ordering and weak magnetocrystalline anisotropy (Ku) impede its practical use in a technologically relevant permanent magnet. Employing density functional and Monte Carlo simulations, we demonstrate the substantial improvements on structural and thermal stability, disorder-order phase transition, and intrinsic permanent magnetic properties of Fe−Ni structures. We propose that this is achievable through the complementary elemental substitutions by metal elements (M) and interstitial doping with 2p elements. Fe1-xMxNi with simple metal (M = Ga and Al) and metalloid (M = Ge and Si) elemental substitutions at x = 0.5 are broadly known as Heusler (L21) structures with no permanent magnet characteristics. On the contrary, we find that for x = 0−0.5, L10-type structure is energetically favored over the Heusler-type structures. The predicted structures exhibit Ku values up to approximately 2.1 MJ/m3, which is roughly three times that of FeNi phase (0.68 MJ/m3), where the absolute value of Ku depends on the degree of L10 crystal ordering. Interstitial doping with B elevates Ku further up to a maximum value of 3.9 MJ/m3 (at 0 K), leading to room-temperature intrinsic permanent magnetic properties, including maximum energy density product (BH)max, anisotropy field μ0Ha, and hardness parameter κ, comparable to the widely investigated MnBi and MnAl permanent magnets. These results may serve as a guideline in designing Fe−Ni based rare-earth free gap permanent magnetic materials that were previously overlooked.

Demagnetization analysis of outer-rotor-type BLDC motors considering permanent magnet overhang structure

This paper presents an analysis of demagnetization of an outer rotor type brushless DC (BLDC) motor with a permanent magnet (PM) overhang structure. The proposed model converts the operating points of PM to consider such a three-dimensional (3D) structure in two dimensions (2D). In addition, the rotor yoke thickness of the proposed model is increased to consider the housing rotor. Ferrite PMs require demagnetization analysis owing to their decreasing coercivity at lower temperatures compared with rare-earth PMs. Hence, demagnetization analysis is conducted using a proposed model while considering, the PM overhang structure. The demagnetization analysis results are compared with the results of proposed model and 3D FEA analyses.

Electromagnetic analysis of permanent magnet-assisted synchronous reluctance motor based on magnetic equivalent circuit

As rare-earth permanent magnet prices continue to fluctuate, interest in non-rare-earth permanent magnet-assisted synchronous reluctance motors (PMa-SynRMs) is increasing. However, non-rare-earth PMa-SynRMs have a multi-layer structure with interior permanent magnets to compensate for the low magnetic fields. Therefore, the rotor has several design parameters, and electromagnetic analysis is time-consuming. To overcome these challenges, magnetic equivalent circuit analysis was used to perform fast electromagnetic analysis of non-rare-earth PMa-SynRMs. In addition, the validity of the proposed method was confirmed through a comparison of the obtained results with those of finite element analysis.

Theory of Defect-Induced Crystal Field Perturbations in Rare-Earth Magnets.

We present a theory describing the single-ion anisotropy of rare-earth (RE) magnets in the presence of point defects. Taking the RE-lean 1∶12 magnet class as a prototype, we use first-principles calculations to show how the introduction of Ti substitutions into SmFe_{12} perturbs the crystal field, generating new coefficients due to the lower symmetry of the RE environment. We then demonstrate that these perturbations can be described extremely efficiently using a screened point charge model. We provide analytical expressions for the anisotropy energy that can be straightforwardly implemented in atomistic spin dynamics simulations, meaning that such simulations can be carried out for an arbitrary arrangement of point defects. The significant crystal field perturbations calculated here demonstrate that a sample that is single phase from a structural point of view can nonetheless have a dramatically varying anisotropy profile at the atomistic level if there is compositional disorder, which may influence localized magnetic objects like domain walls or skyrmions.

Electromagnetic analysis of an axial flow machine with permanent magnets for use in wind turbines

Nowadays, there is a global trend for searching new sources of energy with lower possible aggression to the environment and to humans in generation of electric power. According to the Brazilian Electricity Regulatory Agency (ANEEL), the generation through wind power now is around 1200MW of installed power, and the government has already signed 140 new projects to be installed until the end of 2013, with which the country would produce about 5000MW. This favorable scenario for the development of wind power, leads to several jobs in the area of forecasting and designs of electrical machines for wind turbines. This paper deals with the study of a 50 kW Torus generator with rare-earth permanent magnets applied in wind turbines. Such topology is compact, simple and has a high efficiency.

FEA Analysis and Optimization of Rotor Models in Permanent-Magnet Synchronous Motors fitted with Bonded Rare-Earth Magnets

The Toyota Prius MG2 electric motor and its upgrades, since its first appearance in 1997, are presented in this paper. This electric motor has an Interior Permanent Magnet (IPM) fitted with Rare Earth (RE) magnets, which presents clear advantages over the more widely used Induction Motors (IM). The principal advantage is its high power-density value that makes it a leader in the Electric Vehicles (EV) market. This technology, however, faces a problem, in so far as the global production of RE magnets is an exclusive monopoly of China, (motivating the United States and Japan, among others, to investigate alternative systems). In this paper, the proposal is to substitute the sintered magnet in current use by the bonded type of magnet. The use of bonded magnets permits curved geometric forms, reducing the use of dysprosium, one of the most controversial elements of sintered magnets. These materials are compared using Finite Element Analysis (FEA) in the design of various rotor models including the proposal of a model with bonded magnetic materials, with the advantages of curved magnets and a dual layer arrangement. The proposed rotor model yielded a considerably higher power density than the model developed by Toyota.

Magnetism and fermiology of kagome magnet YMn6Sn4Ge2

Kagome lattice magnets are an interesting class of materials as they can host topological properties in their magnetic and electronic structures. YMn6Sn6 is one such compound in which various exotic magnetic and electronic topological properties have been realized. Here, by means of a partial substitution of Sn with an isovalent and slightly smaller atom Ge, we demonstrate the sensitivity of such chemical substitution on the magnetic structure and its influence in the electronic properties. Magnetic structure of YMn6Sn4Ge2 determined by neutron diffraction reveals an incommensurate staggered magnetic spiral with a slightly larger spiral pitch than in YMn6Sn6. This change in magnetic structure influences the Fermi surface enhancing the out-of-plane conductivity. Such a sensitivity to the partial chemical substitution provides a great potential for engineering the magnetic phases and associated electronic properties not only in YMn6Sn6, but also in the large family of 166 rare-earth kagome magnet.

Magnetization dependent demagnetization characteristic of rare-earth permanent magnets

Magnetization dependent demagnetization characteristic of rare-earth permanent magnets

Forecasting Rare Earth Element Demands for Clean Energy Technologies with the Bass Diffusion Model

The push to decarbonize has spurred the demand for clean energy technologies such as electric vehicles (EVs) and wind turbines (WTs). These technologies rely on rare earth permanent magnets (REPMs), namely Neodymium-Iron-Boron (NdFeB) magnets that in turn rely on rare earth elements (REEs), including Neodymium (Nd), and Dysprosium (Dy). As the demand for clean energy technologies increases, so will the demand for Nd and Dy-containing REPMs. Both Nd and Dy are critical elements that are prone to supply chain risks. As our reliance on them increases, it becomes essential to anticipate future market dynamics for these elements. This paper aims to address the current gap in the literature in the context of forecasting future Nd and Dy demand quantities. The Bass Diffusion Model is a widely used approach to forecast the adoption of new products or technologies and, to predict demand trends. Over the years, the model has found applicability in a wide variety of sectors including consumer durables, medical services, and agricultural innovations. This paper demonstrates the use of the Bass Diffusion Model to estimate future global Nd and Dy demands, enabling a better understanding of swiftly evolving clean energy technology and REPM-related market dynamics.

Techno-Economic Assessment of a Novel Continuous Hot-Roll Process for Manufacturing Nanograin NdFeB Magnets

Rare earth permanent magnets (REPMs) play a pivotal role in clean energy technologies like electric vehicles and wind turbines. However, their reliance on critical materials like dysprosium presents supply risks. This study introduces an innovative manufacturing approach for nanograin NdFeB magnets using a continuous hot-roll deformation process. This method has the potential to eliminate the need for dysprosium, reducing costs and material criticality. A techno-economic assessment (TEA) evaluates the economic feasibility of the proposed approach relative to conventional methods. The novel process amalgamates densification and texture development into a continuous, rapid heating and cooling method, minimizing grain growth. The TEA reveals that for an annual production of 100 metric tons of magnets, the novel method yields profits of $1.31M annually versus losses of $14.15M and $2.51M for conventional sintering and hot-press hot-deformation approaches respectively. Over a 20-year lifespan, the net present value is $21.60M using an 8% discount rate. The price-performance ratio is 10.86 × 103 $/m3/MGOe, which is better than the benchmark for commercial viability. Overall, the hot-roll approach streamlines production, enhances properties, eliminates waste, and improves economics, offering advantages over conventional manufacturing process chains.