Permanent Magnet Properties Research Articles

Effect of cryogenic treatment time on mechanical properties of Sm2Co17 permanent magnets

Sm2Co17 permanent magnets are widely used in aerospace, radar communication, rail transit, and various other fields. However, their brittleness restricts their application. Improving their mechanical properties is of practical interest. Cryogenic treatment can be used as a means to enhance the mechanical properties of Sm2Co17 permanent magnets. However, the specific relationship between cryogenic treatment time and the properties of samarium-cobalt magnets has not yet been fully understood. In light of this, this paper focuses on exploring the influence of cryogenic treatment time on the mechanical properties of Sm2Co17 permanent magnets, aiming to provide a foundation for further elucidating this relationship. The results show that the mechanical properties can be significantly affected by cryogenic treatment time, with the flexural strength and elastic modulus increasing by 27.6 % and 9.6 % respectively when 3 h of treatment. However, the effect of further extending the treatment time to 6 h is not significant. In addition, the cryogenic treatment time has no adverse effect on magnetic properties. Additional analysis reveals that the enhancement in mechanical properties is primarily attributed to the decrease in residual stress and lattice constants. This study provides valuable insights into optimizing cryogenic treatment parameters to enhance the mechanical performance of Sm2Co17 permanent magnets while preserving their magnetic properties.

The Influence of Cu Powders Doping on Magnetic and Mechanical Properties of Sm₂Co₁₇ Permanent Magnets

The Influence of Cu Powders Doping on Magnetic and Mechanical Properties of Sm₂Co₁₇ Permanent Magnets

Magnetic properties of exchange-coupled permanent magnets based on barium hexaferrite and cobalt ferrite nanocomposites

The strategy of blending hard and soft magnetic materials to synthesize nanocomposites offers new possibilities for magnetic materials. We focus on synthesizing and optimizing BaFe12O19-CoFe2O4 nanocomposites using a co-precipitation method to enhance the magnetic properties through exchange coupling. The synthesis conditions including pH, annealing temperature, and blending ratio were systematically investigated. The precursor synthesized at pH 13 produced uniform precipitates, and upon annealing at 1000 °C, barium hexaferrite (BH) and cobalt ferrite (CF) with hexagonal and spinel structure were each formed. The nanocomposite with a blending ratio of 0.75BH-0.25CF exhibited enhanced saturation magnetization and the highest remanent magnetization compared to the individual components. The crystal structure, morphology, and magnetic properties were characterized using X-ray diffraction, field-emission scanning electron microscopy, and vibrating sample magnetometry.

A novel temperature calculation method of canned permanent magnet synchronous motor for vacuum pump

Accurate temperature prediction is vital for the canned permanent magnet synchronous motor (CPMSM) used in the vacuum pump, as it experiences severe heating. In this paper, a novel motor temperature calculation method is proposed, which takes into account the temperature impact on the heat transfer capacity. In contrast to existing electromagnetic-thermal coupled calculation methods, which solely address the temperature effect on the motor electromagnetic field, the proposed method comprehensively considers its impact on motor losses, permanent magnet magnetic properties, thermal conductivity, and heat dissipation ability of motor components, resulting in a motor temperature simulation that closely resembles the actual physical process. To verify the reliability of the proposed temperature calculation method, a 1.5 kW CPMSM was chosen as the research subject. The method was used to analyze the temperature distribution characteristics of the motor and assess the impact of ambient temperature on motor temperature rise. Furthermore, a prototype was fabricated, and an experimental platform was established to test the motor temperature. The results demonstrate good agreement between the calculated results obtained using the proposed method and the experimental data. This research not only provides a theoretical foundation for optimizing the design of the CPMSM but also provides valuable insights into its operational safety and reliability.

Finite temperature properties of rare earth free Fe4CoSi permanent magnet

Developing rare-earth free permanent magnet is attracting extensive research efforts for several device applications and other issues. Here, we investigate the temperature-dependent magnetic properties of the Fe4CoSi alloy. The Fe4CoSi alloy shows a high critical temperature of 980 K with perpendicular magnetic anisotropy. At room temperature, it exhibits a magnetization of 1.44 T, anisotropy constant of 0.8 MJ/m3, and a magnetic hardness parameter of 0.75. We obtain the (BH)max of 554 kJ/m3 at 0 K, 410 kJ/m3 at 300 K, and 215 kJ/m3 at 600 K without demagnetization effect. Even with a demagnetization factor of 0.3, the Fe4CoSi alloy still possesses the (BH)max of 268 kJ/m3 at room temperature. The Fe4CoSi exhibits better permanent magnetic properties compared with ferrites and SmCo5. This may imply that the Fe4CoSi alloy can be a potential Fe-based gap permanent magnet between ferrite and Nd-Fe-B (or Sm–Co) at room temperature.

Modeling of Dual-Phase Composite Magnetic Material and Its Application in Transformers

Dual-phase composite magnetic materials have magnetic and permanent magnetic properties. They can realize the dual-phase conversion of soft magnetic and permanent magnetic composites with a small amount of excitation energy. They have the advantages of good control and conversion characteristics and save energy, and they have a wide range of application scenarios in regard to power equipment. In this paper, the magnetization modeling of dual-phase composite magnetic materials is carried out based on micromagnetic theory, and a specific mathematical expression is given. Secondly, the preparation process of the dual-phase composite magnetic material is studied, the dual-phase composite magnetic material is prepared, and the demagnetization curve of the dual-phase composite magnetic material is measured. Finally, the application of dual-phase composite magnetic materials in power equipment is carried out. Using the soft magnetic and permanent magnetic characteristics of dual-phase composite magnetic materials, their impact on DC bias suppression in transformers is assessed. Magnetic circuit reluctance theory is used to develop the structure and electromagnetic design of a transformer. A transformer prototype with DC bias suppression ability based on dual-phase composite magnetic materials is manufactured, and simulation and experimental research are carried out. The simulation and experimental results verify the correctness of the proposed scheme. Although this scheme requires a more complex core structure, the energy-saving effect is remarkable without changing the transformer’s neutral grounding. The indicators meet the actual requirements of the project.

Image-based prediction and optimization of hysteresis properties of nanocrystalline permanent magnets using deep learning

We demonstrate the use of model order reduction and neural networks for estimating the hysteresis properties of nanocrystalline permanent magnets from microstructure. With a data-driven approach, we learn the demagnetization curve from data-sets created by grain growth and micromagnetic simulations. We show that the granular structure of a magnet can be encoded within a low-dimensional latent space. Latent codes are constructed using a variational autoencoder. The mapping of structure code to hysteresis properties is a multi-target regression problem. We apply deep neural network and use parameter sharing, in order to predict anchor points along the demagnetization curves from the magnet’s structure code. We present a proof of concept for microstructure design of nanocrystalline Nd2Fe14B permanent magnets using image-based machine learning. We show how new grain structures can be generated by interpolation between two points in the latent space and demonstrate inverse design. We show how to compute the granular microstructure that will give a demagnetization curve with a given remanence, squareness, and coercivity through optimization in latent space.

Sensing of Continuum Robots: A Review.

The field of continuum robotics is rapidly developing. The development of new kinematic structures, locomotion principles and control strategies is driving the development of new types of sensors and sensing methodologies. The sensing in continuum robots can be divided into shape perception and environment perception. The environment perception is focusing on sensing the interactions between the robot and environment. These sensors are often embedded on an outer layer of the robots, so the interactions can be detected. The shape perception is sensing the robot's shape using various principles. There are three main groups of sensors that use the properties of electricity, magnetism and optics to measure the shape of the continuum robots. The sensors based on measuring the properties of electricity are often based on measuring the electrical resistance or capacitance of the flexible sensor. Sensors based on magnetism use properties of permanent magnets or coils that are attached to the robot. Their magnetic field, flux or other properties are then tracked, and shape reconstruction can be performed. The last group of sensors is mostly based on leveraging the properties of traveling light through optical fibers. There are multiple objectives of this work. Objective number one is to clearly categorize the sensors and make a clear distinction between them. Objective number two is to determine the trend and progress of the sensors used in continuum robotics. And finally, the third objective is to define the challenges that the researchers are currently facing. The challenges of sensing the shape or the interaction with the environment of continuum robots are currently in the miniaturization of existing sensors and the development of novel sensing methods.

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.

Study on the relationship between structure and magnetic properties of τ-phase MnAl prepared by cryo-milling

The unique characteristics, such as high magnetic moment, high Curie temperature, large magnetic crystalline anisotropy, and low cost, make the τ-phase MnAl a promising candidate as the market alternatives which could fill the gap between the rare earth magnets and ferrite magnets. Because at low temperatures the metal will become more brittle, the cryomilling technology may allow the τ-phase MnAl to be broken quickly and introduce few crystal defects, and then obtain better permanent magnetic properties. In this study, the cryomilling technology was used to grind the τ-phase MnAl, and the structural and magnetic properties of the obtained powder sample were investigated. It was found that compared to room-temperature ball milling, the morphology of cryomilled powders is granular and the powder agglomeration is dramatically suppressed at a low temperature, and as a result the larger particles tend to be broken down into smaller ones rather than being agglomerated to larger thin layers. The grain size D reduced continuously from 145 nm to 36 nm when the sample was milled for 120 minutes. The coercivity increased with increasing the cryo-milling time, while the saturation magnetization decreased. The maximum coercivity of up to 4.9 kOe was obtained by cryo-milling for 100 minutes. By the neutron diffraction analysis, it was confirmed that the decrease of the saturation magnetization with increasing milling time is mainly due to the migration of Mn atoms from 1a site to the 1d site and the decrease of Mn atomic magnetic moment.

Matching experimental chemical composition configuration and theoretical model in Nd2Fe14B/α-Fe nanocomposites to improve coercivity

Matching the experimental chemical composition configuration and theoretical model in Nd2Fe14B/α-Fe nanocomposites to improve coercivity provides reliable guidance for the improvement of the magnetic properties of nanocomposite permanent magnets.

Comparative analysis of a mining truck motor with permanent magnets in a rotor and a synchronous homopolar motor without magnets in a drive

The relevance. Increasing need for using mining trucks with a diesel-electric (hybrid) drive for development of minerals. Improving operational and cost characteristics of the electric drive of mining trucks helps to reduce costs in the development of minerals. The main aim. To compare theoretically the performance of synchronous traction motors of various designs (a conventional design with permanent magnets inside a rotor and a homopolar design without permanent magnets with an excitation winding on a stator), optimized by the same method, in the drive of a mining truck. To optimize the motor design to reduce power loss and required inverter power, as well as to limit torque ripple and reduce the risk of permanent magnet demagnetization. Objects. Design of twelve-pole nine-phase synchronous AC motors with a rated power of 370 kW of various designs: a homopolar motor without permanent magnets with an excitation winding on the stator and a motor of a traditional design with permanent magnets in the rotor. Methods. Derivative-free optimization method; equivalent circuit method; mathematical modeling; two-dimensional finite element method. Results. Based on the analysis, the advantages and disadvantages of the considered motors were revealed. The advantage of the motor with permanent magnets in the rotor is reduction in active part length by 30 %. The advantage of the homopolar motor with an excitation winding on the stator are 4.6 times lower cost of active materials. In addition, the homopolar motor has a more reliable design, without the risk of overheating, demagnetization or deterioration of the properties of permanent magnets over time

Optimizing Co content in intermetallic L10-FeCoPt nanoparticles to enhance the electrocatalytic performance

The L10-FeCoPt nanoparticles with ultra-small size, highly ordered structure, and various Co contents have been successfully obtained by annealing the wet-chemical synthesized nanoparticles. The addition of third-element Co into L10-FePt nanoparticles would increase the grain size, facilitate the disorder-order transition, and enhance the saturation magnetization and coercivity. The better permanent magnet properties and maximum electrocatalytic HER activity of L10-FeCoPt nanoparticles were achieved when added the moderate Co content (4.5 % and 8.5 %). The hydrogen evolution reaction (HER) kinetics and density functional theory revealed that the Co atom would promote the hybridization of Fe-3d and Pt-5d orbitals and increase the hydrogen adsorption free energy to closer to 0. Optimization of Co content to a suitable range would generate higher permanent magnetic properties and suitable surface energy, which facilitated the proton transformation and lowered the Tafel slope to follow the Volmer-Tafel process in HER. This work illustrates that optimizing third-element content in Pt-based magnetic intermetallic is a feasible strategy to operate the electrocatalytic reaction pathway and enhance the electrocatalytic performance.

Microstructure and magnetic properties of binary Mn54-Al46 alloy particulates obtained by severe plastic deformation processing via end-milling and annealing

We utilize the plastic deformation process associated with the machining operation of end-milling for the preparation of ε-phase Mn-Al particulates with micron scale external dimensions and self-similar shapes from binary as-cast feedstock with composition 54 at.% Mn and 46 at.% Al. The structural evolution and development of magnetic properties in response to the single-pass plastic deformation processing by the end-milling and subsequent thermal annealing have been studied. Effects of end-milling process parameter combinations, primarily the rotational speed of the cutting tool, have been identified to permit genesis of morphological self-similar particulates of ε-phase characterized by cold-worked and sub-micron to nanometer scale refined microstructures. The end-milling derived particulates were suitable for preparation of τ-phase based MnAl particulates with enhanced permanent magnet properties via isothermal annealing. Discernibly higher rates for the exothermic ε-phase decomposition reactions in the end-milling derived particulates have been observed for isothermal annealing at temperatures in the range of 673 K ≤ T ≤ 723 K. The enhanced decomposition reaction kinetics have been attributed to reduced effective nucleation barriers for the respective product phases stemming primarily from reduced grain size. Large saturation magnetization and coercivity in combination with reasonable squareness ratios of the magnetization curves resulted in a (BH)max = 4.2 MGOe for the end-milling derived binary Mn54Al46 particulates obtained for the highest rotational tool speed of 4200 RPM used here after annealing for 20 min at 673 K. The ε-phase Mn-Al particulates derived by end-milling have potential as precursors for the fabrication of τ-phase Mn-Al based PM materials.

Preparation and magnetic properties of magnetically anisotropic 2:17-type SmCo alloy spherical particles

This study utilized the irregular Sm(Co0.69Fe0.22Cu0.07Zr0.02)8.1 alloy powder as the primary material, combining the solid/liquid interface de-wetting effect and abnormal grain growth method for preparing the 1:7-type SmCo spherical single crystal powder. Through aging heat treatment, the anisotropic 2:17-type SmCo alloy spherical permanent magnetic powder with size distribution of 30–130 μm was successfully obtained. The study explored the spheroidization mechanism and single crystal growth rule of Sm(Co0.69Fe0.22Cu0.07Zr0.02)8.1 alloy powder, as well as the impact of solution-aging magnetic hardening treatment on the permanent magnet properties. The optimized permanent magnetic properties of the resulting 2:17-type SmCo alloy spherical powder were coercivity Hic = 1244 kA/m, and maximum magnetic energy product (BH)max = 224.5 kJ/m3 at room temperature. The anisotropic 2:17-type SmCo alloy spherical magnetic powder prepared using this method exhibits significant potential applications in the production of bonded magnets.

Large energy product of rare earth free Fe3MnC2 alloy permanent magnet

Due to the importance for device applications and also other subtle issues, study on rare-earth free permanent is becoming more and more important subject. Here, we investigate the temperature dependent magnetic characteristics of the Fe3MnC2 structure. We find that the Fe3MnC2 alloy exhibits a critical temperature of 640 K with perpendicular magnetic anisotropy. With increasing temperatures, both the coercive field and the magnetic anisotropy constant monotonically decrease. From temperature dependent magnetization and coercive field, the (BH)max of the Fe3MnC2 system obtained is 396 kJ/m3 at zero Kelvin. The (BH)max suppressed with increasing temperature. Nonetheless, we find the (BH)max of 253 kJ/m3 is at 300 K. Compared with the (BH)max of ferrites and SmCo5, the Fe3MnC2 alloy structure exhibits better permanent magnetic properties. Therefore, we suggest that the Fe3MnC2 could be a suitable candidate for a Fe-based gap permanent magnet between ferrite and Nd-Fe-B (or Sm-Co) at room temperature.

Amorphous-crystalline nanostructured Nd-Fe-B permanent magnets using laser powder bed fusion: Metallurgy and magnetic properties

Laser powder-bed fusion (PBF-LB), a class of additive manufacturing (AM), has attracted wide interest in the production of Nd-Fe-B permanent magnets, benefiting from the minimisation of waste of rare-earth elements and the post-processing requirements. Most research on PBF-LB Nd-Fe-B has focused on reducing defects in printed parts alongside the improvement of the resultant magnetic properties. Detailed analysis of the microstructure that results in permanent magnetic properties is yet to be published. In this research, a combination of high-resolution microstructural investigations was conducted for this purpose. For the first time, an in-depth analysis of the grain structure in terms of morphology, size distribution, and texture is presented and correlated to the permanent magnetic performance. Melt pools showed a hierarchical grain size distribution of primary Nd2Fe14B phase grains with a polygonal morphology and random crystalline alignment, in addition to a small amount of Nd-rich and Nd-lean precipitates in the matrix of the Ti-rich amorphous grain boundaries. The permanent magnetic properties of this material are mainly determined by the nanostructured Nd2Fe14B grains and the amorphous Ti-rich iron-based intergranular phase but could be weakened by precipitates that act as magnetic pores. Remelting during PBF-LB led to the transformation of the coarse grains of the previously solidified layer to fine ones, favourable for the permanent magnetic properties. The mechanisms of these complex phase formations and transformations during processing and the development of the nanocrystalline microstructure are elucidated in this paper as a basis for informing the optimisation process for microstructural development.

Significant coercivity enhancement of Ga-doped sintered Nd-Fe-B magnet by grain boundary diffusion perpendicular to the c-axis

Grain boundary diffusion (GBD) process is the most effective approach for enhancing coercivity of Nd-Fe-B magnets with minimal consumption of heavy rare earth (HRE). However, understanding of GBD mechanism is still limited, especially on the anisotropic diffusion behavior within sintered magnets. Grain boundary (GB) phase is the key factor in determining the diffusion process, which acts as diffusion channel for HRE atoms. The effects of doping Ga on the grain boundary microstructure and diffusion behavior of Tb in the sintered Nd-Fe-B magnet were investigated. Sintered magnets with different Ga content (0.15 wt%, 0.45 wt%) were prepared. It should be noted that Tb was diffused perpendicular to the easy axis (c-axis) of the magnets. The coercivity increased more significantly to 2.802 T (1.006 T higher than that of the post-sinter annealed state) in magnets with high Ga content than the low Ga content magnets (2.291 T, 0.669 T higher than the post-sintered annealed state). Such a huge coercivity increment almost reached the same value by diffusing Tb along the easy axis reported by other researchers. Chemical compositions and microstructure of the GB phase were found to be key factors in influencing the HRE diffusion process. A considerable amount of Nd6Fe13Ga phase was observed near triple junctions after post-sinter annealing in the high Ga content magnets, which markedly decreased Fe concentration in the intergranular phase. In addition, amorphous intergranular metallic Cu-rich phases provided smooth diffusion channels for HRE atoms. (Nd1-x, Tbx)2Fe14B shell was much more obvious in the high Ga content magnets. Ga dopping induced novel modifications in diffusion behavior of HRE atoms and strongly influenced the magnetic properties of permanent magnets. The present approach provide new path for the manufacture of high performance magnets, which is interesting both for technical applications and fundamental studies.

Chemical segregation mechanism and magnetic properties of Sm2Co17-based permanent magnets: experimental investigation and first-principles calculations

The magnetic properties and chemical segregation have led to an increased interest in Sm2Co17-based magnets. This investigation employs experiments and first-principles calculations to obtain more profound comprehension of segregation and coercivity mechanism. The Sm(CobalFe0.25Cu0.06Zr0.02)7.5 alloy exhibits a chemically heterogeneous cellular structure with Fe-rich 2:17R cells (60–70 nm) and Fe- and Cu-rich 1:5 cell boundaries (8–10 nm), and achieves excellent magnetic properties with a Br of 11.69 kGs, an Hcj of 30.96 kOe and a (BH)max of 33.0 MGOe. First-principles calculations are performed on Sm6Co51–xMx and SmCo5–yMy (M = Fe, Cu) unit cells to identify their substitution energy (Es) and electronic structure. In Sm6Co51–xMx, Fe atoms preferentially occupy the 6c and 18f Co sites, whereas Cu replacement is unlikely to occur due to its positive Es values. The segregation of Fe into the 2:17R structure is due to the decrease in the total density of states (DOS) at the Fermi level (EF) and the introduction of Fe-Co covalent-like bonding. By comparison, Fe and Cu atoms are both helpful for stabilizing the 1:5 phase, with Cu atoms first occupying the 2c site (Es = −1.697 eV/f.u.) and Fe atoms first occupying the 3g site (Es = −1.627 eV/f.u.). This small energy difference further explains the existence of Fe atoms in the 1:5 phase during ageing, which could significantly increase the magnetization. The segregation of Cu to the 1:5 phase is attributed to the formation of a pseudogap or bandgap at EF. Ultimately, we furnish an extensive elucidation of the commonly acknowledged domain wall pinning coercivity mechanism at ambient temperature according to SmCo5–yCuy cell boundary phases.

原子論的スピンモデルによる永久磁石の磁気特性の研究 ―熱揺らぎおよび温度効果の取り扱いと将来展望―

We review atomistic spin model studies, a new approach for theoretical investigations, on magnetic properties of permanent magnets. In the atomistic modeling, the microscopic details of magnetic parameters and lattice structures are realistically considered, and the temperature effect, including thermal fluctuation, is properly treated based on statistical physics methods: Monte Caro methods and stochastic Landau-Lifshitz-Gilbert equation methods. We introduce how to treat thermal effects for static and dynamical properties using these methods. Focusing especially on neodymium permanent magnets, we discuss features of magnetization, domain wall, coercivity of a grain, nucleation and pinning fields, and dysprosium substitution effect, which were first elucidated with those methods.