Rare-earth Magnets Research Articles

Quality control in workshop production of NdFeB magnetic materials using an LIBS rare earth magnet instrument

An LIBS rare earth magnet online measuring instrument was used to classify and test NdFeB crude samples produced in the Baotou Rare Earth Research Institute workshop. The classification accuracy was increased from 87.14% to 99.05%.

Features and Applications of Bonded Rare Earth Magnets

Features and Applications of Bonded Rare Earth Magnets

Suppression of anti-phase boundary defects in Mn-Al-Ti permanent magnets

Permanent magnets (PMs) based on manganese show significant potential for applications in electric motors and devices as an alternative to Rare-earth PMs (REPMs). The metastable ferromagnetic τ phase of the Mn-Al system has magnetic performance between the REPM Nd-Fe-B magnets and the lower performance ferrite magnets. However, the maximum performance in Mn-Al PMs has not reached its theoretical limit, in part due to challenges in controlling crystalline defects such as anti-phase boundaries (APBs). APBs act as nucleation sites for domain reversal in Mn-Al and negatively affect magnetization by interrupting the L10 ordering, placing Mn atoms into AFM-coupled Mn-Mn configurations. In this study, Ab-initio modeling was used to screen ternary elements based on their affinity to segregate to the APB and on their preference for FM configuration. The ternary element addition of 1 at.% Ti lowered the density of APBs as observed in a transmission electron microscope. The 1 at.% Ti addition was observed to improve (BH)max over the base alloy, by preserving Hci and improving Mr. It also significantly increased the fraction of twin boundaries in the τ phase. AFM behavior that was observed in the base alloy during TC heating experiments (Néel behavior) and high-field VSM measurements (spin-flop behavior) was effectively suppressed with the addition of Ti. Additionally, the Ti addition thermally stabilized Hci at 550 °C, improving τ phase processability. Other candidate elements, Cr, V, and Zr, were modeled to have similar potential for minimizing APBs when added to Mn-Al.

Behavioural response of benthic elasmobranchs to a neodymium magnet under controlled laboratory conditions

Global elasmobranch population decline can be largely attributed to anthropogenic impacts such as commercial fishing. As such, reducing bycatch of these animals is a key management objective in many fisheries. Magnetic deterrents such as permanent and rare-earth magnets can deter both pelagic and benthic elasmobranch species. However, the literature is inconsistent and shows varied levels of effectiveness depending on the species and the deterrent. To broaden our understanding of species-specific differences in deterrent effectiveness, this study assessed the efficacy of a rare-earth magnet to deter four benthic elasmobranchs under laboratory conditions: Port Jackson shark (Heterodontus portusjacksoni; n = 10), epaulette shark (Hemiscyllium ocellatum; n = 8), eastern fiddler ray (Trygonorrhina fasciata; n = 10), and the blue spotted mask ray (Neotrygon kuhlii; n = 7). After evaluating the behavioural response of the four study species in the presence of a N52 neodymium magnet and a control in 207 trials, the neodymium magnet did not effectively prevent individuals from entering an experimental compartment. The magnet only had a minor deterrent effect, slightly reducing the proportion of successful attempts at entry through the door and over the neodymium magnet (control: 0.94 ± 0.23; neodymium magnet: 0.74 ± 0.3; mean ± standard deviation). We hypothesised this was a result of species-specific biological and behavioural factors that reduce the effectiveness of magnets as deterrents for these species. Our results suggest fisheries management moves away from trialling magnets as elasmobranch deterrents due to their inconsistent effectiveness, and rather investigate other devices such as those using electrical fields that show greater potential.

Torque Ripple and Mass Comparison between 20 MW Rare-Earth and Ferrite Permanent Magnet Wind Generators

This article investigates the comparison between two configurations of 20 MW offshore synchronous wind generators using ferrite and rare-earth permanent magnets. The optimization-based comparison concerns the torque ripple and active mass, which are two crucial criteria for offshore wind generators. Both generators adopt surface-mounted permanent magnet type with direct-drive technology to avoid problems associated with the gearboxes. The result shows that at the full-load condition, the ferrite permanent magnet generator can reduce the torque ripple to as much as 0.12%, while the rare-earth counterpart can be about 2.5 times lighter than the former one.

Multi-sensor information fusion localization of rare-earth suspended permanent magnet maglev trains based on adaptive Kalman algorithm.

Since the positioning accuracy of sensors degrades due to noise and environmental interference when a single sensor is used to localize a suspended rare-earth permanent magnetically levitated train, a multi-sensor information fusion method using multiple sensors and self-correcting weighting is proposed for permanent magnetic levitated train localization. A decay memory factor is introduced to reduce the weight of the influence of historical measurement data on the fusion estimation, thus enhancing the robustness of the fusion algorithm. The Kalman filtering results suffer from inaccuracy when process noise is present in the system. In this paper, we use a covariance adaptive scheme that replaces the prediction step of the Kalman filter with covariance. It uses the covariance adaptive scheme to search the posterior sequence online and reconstruct the prior error covariance. Since the process noise covariance is not used in the new adaptive scheme, the negative impact of the mismatch noise statistics is greatly reduced. Simulation and experimental results show that the use of multi-sensor information fusion and covariance adaptive Kalman algorithm has significant advantages in terms of adaptability, accuracy and simplicity.

Enhancing structural and magnetic properties of BaFe12O19 nanoparticles through co-substitution (Co-Mn): A promising approach for permanent magnet applications

In-depth study into the creation and improvement of rare-earth free permanent magnets, particularly ferrites, has been sparked by recent economic and environmental concerns. M-type barium hexaferrites (BaFe12O19, pure BHF) are a class of low-cost permanent magnets with an excellent curie temperature and good resistance to oxidation and corrosion that are significant from a technological perspective. In the current study, the experimental conditions are optimized to obtain barium hexaferrite (BaFe12O19) co-substituted with transition elements (Co and Mn) (BaFe12–2xCoxMnxO19) via the chemical co-precipitation method. In this framework, different substitution possibilities will be investigated. The structure, morphology, vibrational spectrum, and thermal stability of the generated nanoparticles were revealed using powder x-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Rietveld refinement was used to estimate the average bond length and bond angle in order to determine the impact of superexchange interaction. Based on more precise structural characteristics, the atomic occupation and distribution of bonds are depicted from their charge density graph. For all the synthesized materials, the maximum energy product (BH)max and magnetic characteristics (VSM) were also investigated. The potential causes of this phenomenon were examined and discussed at length.

Research on Rotor Loss and Rotor Structure Optimization of Rare Earth Permanent Magnet Synchronous Motors in the Weak Field Area

The rotor loss of rare earth permanent magnet synchronous motor (PMSM) affects the efficiency and reliability of the motor and is an important research direction of rare earth permanent magnet synchronous motors. In this paper, the influence of rotational speed on the loss of the rotor core and the permanent magnet is analyzed through the analysis of the motor magnetic field and rotor loss calculation. Specifically, with the increase in rotational speed, the weak magnetic current increases, the amplitude of flux density change in the rotor core decreases, and the loss of the rotor core also decreases. The greater the influence of the harmonic current magnetic field on the outside of the rotor, the greater the loss. The core loss on the rotor is mainly distributed on the outside of the rotor. For further engineering applications, this paper analyzes the loss composition of three kinds of motors with different rotor structures and judges the optimal scheme based on the minimum loss. Finally, the correctness of this research is verified by comparing the experimental and simulation results of two kinds of motors with different rotor structures. The research content of this paper can provide a reference for the loss analysis and optimization and rotor structure selection of rare earth permanent magnet synchronous motor rotor design.

Effect of Permanent Magnet Structure on Working Characteristics of LSPMSM 3000 rpm

Reducing the cost of electricity to improve production efficiency is one of the urgent tasks. Nowadays, the rapid development of Neodymium rare earth (NdFeB) permanent magnet technology has promoted the creation of high-efficiency motors to replace low-efficiency induction motors to save electricity. One of them is a line-start permanent magnet synchronous motor (LSPMSM). The permanent magnet configuration significantly affects the operating characteristics of the LSPMSM, such as working current characteristics, pulsating torque, working efficiency, and starting speed. The content of the article focuses on investigating and evaluating some permanent magnet configurations affecting the working characteristics of the LSPMSM based on the finite element method through Ansys/Maxwell software. The research results are suggested for the design and manufacture of LSPMSM used in mining to save electricity.

Magnetocaloric Effect in Rare-Earth Magnetic Materials

Abstract—A study of the magnetocaloric characteristics of rare-earth magnets was carried out. There were studied a systems Gd–H, (Gd,R)Ni–H containing hydrogen (R is a rare earth metal); system RCo2–H with the structure of Laves phases; and systems without hydrogen, such as RTX intermetalic compounds (T = Mn, Fe, Co; X = Si), R2(Fe,T)17 compounds (T = Al), which have a magnetic compensation point and exhibit an alternating magnetocaloric effect (MCE). The MCE was measured by the direct method and calculated indirectly from the field dependences of the magnetization. The main regularities are established and the specific features of the formation of magnetocaloric properties are revealed depending on the composition and structure.

Leaching of Rare Earth Elements from Permanent Magnet Swarf in Citric Acid: Effects of Acid Concentration on Extraction Kinetics

The high demand for rare earth permanent magnets (REPMs) for use in advanced electrical equipment has led to the classification of some rare earth elements (REEs), such as neodymium, praseodymium, and dysprosium, as strategic raw materials by the European Union. Finding an efficient method with economic benefits and minimal environmental impact is one of the challenges of recycling REPMs. A novel method to recover REPM metals by dissolving them with citric acid and separating the rare earth elements using the solvent extraction method as the next step has been introduced. Therefore, this research investigates the efficiency and kinetics of leaching REPM swarf by citric acid (0.5 to 2.5 M). The results showed that increasing the citric acid concentration from 0.5 M to 1.45 M significantly enhanced the dissolving rate of all studied elements. Although the results showed that the optimal concentration of citric acid in the leaching reagent was between 0.9 and 1.45 M, the REE dissolving reaction with a leaching reagent containing 1.45 M and 0.9 M citric acid reached equilibrium conditions at about 120 and 180 min, respectively. It could be concluded that using citric acid as an organic acid can dissolve the metals in REPM swarf with high efficiency and a fast dissolving rate. This issue can be considered key for recycling REPMs and the future REE supply challenge.

A new strategy for improving the Tb utilization efficiency in sintered NdFeB magnets through pressure-assisted grain boundary diffusion

Improving the utilization efficiency of heavy rare earth is currently a research hotspot in the field of rare earth permanent magnets. In this article, the effect and mechanism of pressure-assisted grain boundary diffusion (PGBD) on improving Tb utilization efficiency was investigated. The magnetic properties, microstructure, and magnetic domain morphology of the PGBD magnets were compared and analyzed in relation to conventional grain boundary diffusion (CGBD) magnets. The results shows that the PGBD process promoted Tb diffusion into the magnets. The residual layer thickness of the PGBD magnets was thinner than that of the CGBD magnets, demonstrating that the PGBD process could allow more Tb to diffuse into the magnets. The formation of a more complete and deeper core-shell structure in the PGBD magnets significantly enhances their resistance to demagnetization fields, thereby resulting in an increased coercivity. The PGBD process exhibits a reduction in TbH3 usage by approximately 0.2 wt% compared to the CGBD process, while maintaining an equivalent level of coercivity increment. These findings highlight the efficacy of the PGBD process in enhancing Tb utilization efficiency and conserving Tb resources.

Multiple magnetic transitions induced by Mn-doping in orthochromite HoCrO3

It has been established that both hybridization with magnetic rare earth cation and crystal field originating from structural anisotropy can affect the spin orientation of magnetic transition metal perovskite. In this work, we have systematically studied the crystal structure, magnetization, and magnetic structure of Mn-doped rare earth orthochromites HoCr1−xMnxO3 (x = 0–0.85) by means of X-ray diffraction, magnetometry, and neutron powder diffraction. With increasing Jahn–Teller active Mn3+-substitution for Cr3+, the crystallographic distortion is gradually enhanced and causes a systematic evolution of magnetism. With doping, the Cr(Mn) ordering temperature is gradually suppressed, and multiple magnetic configurations Γ2, Γ1, and Γ4 phases appear consecutively. The rich transition phenomena are ascribed to a competition between increased structural anisotropy and weakened Ho-Cr(Mn) hybridization with doping. In a low doping regime with x = 0.1–0.5, Γ2 phase is predominant in low temperature, and a magnetization reversal is observed, reflecting the opposite sign of Cr-Mn DMI coefficient with respect to the Cr-Cr and Mn-Mn interaction. In the high doping range with x = 0.6–0.8, the long-range order of Cr(Mn) sublattice is gradually suppressed while a short-range order becomes dominant. For x = 0.85, a magnetic structure resembling o-HoMnO3 is observed.

Mechanochemical synthesis of MnBi/Fe3C@C exchange coupled hard magnetic nanocomposites

Despite the better suitability of rare earth permanent magnets for various applications, the scarcity of rare earths limits their application range. The, low temperature phase of MnBi is sought as a probable gap magnet without any rare earth elements. Further, the nanocomposites (soft/hard magnets) are known to provide better properties. In this study, Mn55Bi45/Fe3C@C nanocomposites with enhanced magnetic properties were prepared using cryogenic ball milling. The feasibility of utilizing Fe3C@C as a soft phase in hard-soft composites was explored. Fe3C@C was synthesized through the solvothermal technique, followed by calcination, resulting in a remarkable saturation magnetization (MS) of 150 emu/g. Different amounts of Fe3C@C (0, 5, 10, 15, and 20 wt.%) were added to Mn55Bi45 powder, and after cryo-milling, it was observed that the addition of 10 wt. % yielded the optimum results, with a 37% enhancement in MS and 58% increase in Mr values. The presence of exchange-coupled nanocomposites was confirmed through x-ray diffraction, transmission electron microscopy, and magnetic studies. This study not only paves the way for increasing the energy product of the MnBi system but also explores the potential of utilizing Fe3C@C as a soft phase—a relatively oxidation-resistant phase—in other hard magnetic systems.

Modelling and simulation of electrical analogous for permanent magnet materials

Expressions to simulate the intrinsic demagnetizing curve of permanent magnets are derived from the classical electrical analogy of a 2RLC circuit as an equivalent to a magnet under demagnetization in a closed magnetic circuit. Comparisons between experimental and theoretical intrinsic M x H curves were carried out for hard magnetic materials, and the possibility of using this analogous circuit with two components has also been investigated. The demagnetization curves of permanent sintered magnets have been simulated with time domain analytical expressions obtained using an electric equivalent circuit analogous to a closed magnetic circuit. This has been carried out for magnets measured at room temperature and at 373 K. Equivalent electric parameters influenced the various regions of the demagnetization curve. It has also been shown that it was possible to simulate the demagnetization curve of rare earth magnets and also other types of permanent magnets. The Stoner-Wohlfarth model theoretical curves have also been used as a comparison. At last, the electrical analogous parameters have been systematically varied in order to correlate them to the magnetic properties.

Sourcing, Refining and Recycling of Rare-Earth Magnets

Permanent magnets today are used in a wide range of transportation, industrial, residential/commercial, consumer electronics, defense, domestic, data storage, wind energy, and medical markets and applications. There are five classes of commercial permanent magnet materials; however, magnets based on Nd-Fe-B account for over 60% of the global magnet production by value. They typically contain around 31 wt.% of rare earth elements (REEs), principally, Nd and Pr, plus Dy for higher-temperature performance. Nd-Fe-B magnets are forecast to grow throughout this decade, largely driven by the growth in electric vehicles of all types. However, several studies forecast a shortfall of the primary REEs from mined resources. In this paper, the sourcing, processing, and recycling of REEs are discussed. Additionally, presented are the advantages and disadvantages of the major recovery and recycling technologies for REEs.

Structural and physical properties of YbCu4Ni based heavy fermion compounds

Rare-earth magnetism in the intermetallic materials YbCu4.2Ni0.8 and Yb0.8Lu0.2Cu4Ni was studied by XRD, magnetization, electrical resistivity and heat capacity measurements. The results from the sample YbCu4.2Ni0.8 include a small amount of the monoclinic superstructure of the cubic AuBe5. Therefore, the formation of a cubic AuBe5 solid solution of YbCu5-xNix is negligible, and consequently, it cannot be used to reach a quantum critical point.

Enhancing the performance of rare-earth free permanent magnets: A computational study of nitrogen and oxygen defects in CoPt, CoFePt2, and CoNiPt2 alloys

This work presents a computational investigation utilizing density functional theory and Monte Carlo simulations to study the influence of nitrogen and oxygen defects on the structural and magnetic properties of CoPt, CoFePt2, and CoNiPt2 alloys. The goal of this study was to explore their potential applications as alternatives to rare-earth permanent magnets. Our findings have revealed that the incorporation of nitrogen and oxygen defects significantly influence the magnetic properties of these alloys. The incorporation of defects yields negative formation energies, thereby confirming the structural stability of the defective structures. In addition, phonon dispersion calculations further confirmed the dynamical stability of the defective structures with lower formation energies. Notably, the Curie temperature (Tc) of CoFePt2 increased upon the addition of nitrogen, while the magnetocrystalline anisotropy energy (EMCA) of CoNiPt2 was enhanced by the presence of oxygen. In contrast, no improvement in the saturation magnetization was observed. These results provide valuable insights toward the development of rare-earth-free permanent magnets with tailored magnetic properties.

Computer numerical simulations for accelerated design of rare earth permanent magnet motors in renewable energy applications: A review

Rare earth permanent magnet (REPM) motors underpin various emerging fields in electronic and mechanical industries. The rapid growth of renewable energy industries requires the higher performance of the REPM motors, such as the high output torque (≥ 350 N·m), high power (≥ 200 kW), and low ripple torque (< ±5%). To achieve these performances, the fine design for the materials and structures of the REPM motor is required. Computer numerical simulations play important roles in shortening the period and reducing the cost of REPM motor design. Finite difference method (FDM) and finite element method (FEM) are common methods for motor design. Boundary element method (BEM) exhibits advantage in accuracy and efficiency but its commercialization is slower. These three methods have their own advantages and applications. This review discusses the principles and present applications of the FDM, FEM and BEM in details. At present, the electromagnetic and structural simulations are mainly realized by FDM and FEM, while the acoustics simulation is carried out by BEM or combined FEM-BEM. The advantages and limits of various simulation methods in different parts of motor design are comprehensively compared. The recent progress of computer numerical simulations in REPM motor design is summarized, including the simulations in permanent magnets, electromagnetics properties, structure and acoustics characteristics in REPM rotor. In particular, the design of material and electromagnetic structure for the cutting-edge Nd-Fe-B rotor is highlighted. The opportunity and future directions of computational simulations in REPM motor design are also discussed in this review.

Experimental investigations with Neodymium – Iron – Boron magnets with aluminum circular plates to find deceleration, time taken and stopping distance

There are quite a lot of problems in friction brake like squealing, peddle pulsation, structural failure due to high heat, circular plate distortions. Hence, the present work tries to focus on developing no contact brakes by applying induced magnetization principles. Aluminum circular plate along with Neodymium – Iron – Boron (NdFeB) rare earth magnets are chosen for the work. Thickness of circular plates considered are 4, 6 and 8 mm. Chosen Aluminum circular plates are rotated at velocities of 20.94 m/s, 31.39 m/s, 41.89 m/s and 52.36 m/s. Considered brake parameters are brake deceleration, time elapsed for braking and stopping distance. In solitary magnet situation under steady application, aforesaid brake parameters are inferior as compared to those in solitary magnet with swift application situation. Brake parameters were found to be quite superior in 4 mm thick circular plate in solitary magnet with swift application. Considering the parameters such as time elapsed for braking and stopping distance, no contact brakes with permanent magnets are very suitable for top velocity rail applications.