Nanocomposite Permanent Magnets Research Articles

Closed-Loop Analysis of Nanocomposite Magnets: Integrating Micromagnetic Simulation and Experimental Testing

This study presents a framework for simulation-experiment closed-loop analysis of nanocomposite magnets. Firstly, hysteresis loops of nanocomposite permanent magnets were calculated using micromagnetic simulations. Then, the experimental preparation was carried out by rapid quenching of the melt and spark plasma sintering (SPS). We analyzed the effect of different sintering temperatures on the physical phase composition and magnetic properties of the samples. Characterization results show that the samples sintered at 600 °C have the highest magnetic energy product. Using transmission electron microscopy data, the polycrystalline model was refined, and further micromagnetic simulations were performed. The close agreement between simulated and experimental data confirms the improved accuracy of our simulation model. This iterative process of experimental characterization and simulation improvement reduces the discrepancy between simulation predictions and actual sample performance. It could facilitate rapid iteration in magnet development and provide valuable insights for optimizing the preparation of nanocomposite permanent magnets.

Effects of Ti on the solidification and crystallization behavior of nanocomposite permanent material under different cooling rates

Effects of Ti on the crystallization behavior, phase composition, microstructure and magnetic properties of Nd2Fe14B/α-Fe dual-phase nanocomposite permanent magnet materials in different states were studied, respectively. The results show that Ti could affect the solidification and crystallization behavior of dual-phase nanocomposite materials by regulating the cooling rate during the rapid solidification process. When the cooling rate is slow, part of Ti atoms enters the soft magnetic phase α-Fe, and part forms the TiFe2 phase around the hard magnetic phase. Exchange coupling is enhanced. The maximum energy product and the remanence of the alloy are 10.54 MGOe and 8.34 kGs, respectively. When the cooling rate faster, Ti can stabilize another ferromagnetic ThMn12-type phase with a low coercivity and maximum energy product, which should be avoided. When the cooling rate is fast enough to form amorphous, Ti and Fe preferentially combine to form the TiFe2 phase during crystallization, which selectively inhibits the growth of the hard magnetic phase and the precipitation of the soft magnetic phase, resulting in a significant enhancement of coercivity to 12.82 kOe. By regulating the mechanism of Ti in the solidification and crystallization process, nanocomposite permanent magnet materials with varying magnetic characteristics can be obtained, offering a flexible approach to tailoring their performance according to specific application requirements.

Dependence of Nucleation Field on the Size of Soft Phase in Magnetic Hard–Soft Exchange Coupling Nanocomposites

Hard–soft exchange coupling nanocomposites have critical applications in various important materials. The magnetic properties of nanocomposite permanent magnetic films improve with a higher nucleation field (Hns) of the soft magnetic phase. Hns is sensitive to the thickness (ds) of the soft magnetic layer. Understanding the dependence of Hns and irreversible field (Hirr) on ds, especially at the nanometric scale, is crucial for comprehending the magnetic mechanism and facilitating the design and preparation of high-performance nanocomposite permanent magnets. However, during the high-temperature deposition process, diffusion between hard and soft magnetic phases occurs, leading to the generation of other phases. This makes it challenging to accurately reflect the relationship between Hns and ds. To address this issue, we successfully fabricated high-quality SmCo5/Fe nanocomposite bilayer films with different soft magnetic thicknesses and high textures by controlling the preparation process. We conducted a quantitative analysis of the relationship between Hns and ds within the range of 2–40 nm. Based on the experimental results, we propose a new theoretical simulation formula that enhances the understanding of the characteristics at the interface between the soft magnetic and hard magnetic phases. The theoretical simulation results show that a thin softened hard layer of about 4–6 nm thickness exists at the interfacial region, which concurrently reverses with the soft magnetic phase during the demagnetization process. Our results offer the generality and critical basis for the further study of hard–soft nanocomposite magnetic materials.

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.

Effect of hyperfine structure on crystallization, microstructure and magnetic properties of amorphous Nd9Fe85B6 alloy

Crystallization of amorphous alloy is a commonly used method to fabricate nanocomposite permanent magnets. However, the effect of the hyperfine structures of amorphous alloy on microstructure evolution and magnetic properties of the obtained nanocomposites is far from understood. Here, amorphous Nd9Fe85B6 alloys with different hyperfine structures, i.e., different short-range orders (Rs = 0.80–0.91 nm), were prepared via melt spinning. The effects of the hyperfine structure on crystallization behavior, microstructure, and magnetic properties of the material upon thermal annealing were investigated in depth. Crystallization kinetics calculations show that a larger Rs leads to a smaller apparent crystallization activation energy, which leads to higher volume fractions of α-Fe and Nd2Fe14B. At the same time, a crystallizaition process dependent stage crystallization activation energy of Nd2Fe14B has been obtained, which is low at nucleation stage and increases with crystallization process, i.e. easy for nucleation but hard for growth, which leads to a smaller grain size of Nd2Fe14B. As a result, optimized magnetic properties were obtained in the sample with Rs = 0.91 nm.

A combined-pole permanent magnet synchronous motor incorporating nanocomposite magnets

The development of rare earth permanent magnet materials has made outstanding contributions to the advancement of high performance permanent magnet synchronous motors (PMSM). However, the non-renewable and strategic protection of rare earth resources leads to price fluctuations and supply risk of rare earth permanent magnets, limiting electrical vehicle development and popularity. In this paper, we optimized the design of the nanocomposite magnet microstructure and proposed a combined-pole interior nanocomposite permanent magnet synchronous motor (CP-INPMSM), combining nanocomposite magnet and PMSM. The simulation results show that the no-load back-electromotive force and torque of the motor are improved. This design can reduce the usage of rare-earth permanent magnet materials and improve the electromagnetic performance of the motor.

Microstructure evolution of hot-deformed SmCo-based nanocomposites induced by thermo-mechanical processing

• The two-stage phase transition occurred successively, accompanied by grain growth. • Texture formed in 1:5H phase, not in 2:17R phase in SmCo-based nanocomposites. • Proposed a new strategy for forming c-axis textures in nanocomposites. Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products, due to coupling of the soft/hard magnetic phases, inciting strict microstructural requirements. In this study, the microstructure evolution, including the phase transition, morphological changes, and texture formation, of hot-deformed SmCo-based nanocomposites under thermal–stress–strain coupling was characterized to determine a possible strategy for achieving high performance. The SmCo 5 /α-Fe nanocomposites precursor contained fine and dispersed Sm(Fe, Co) 5 and Fe-Co grains and exhibited a two-stage phase transformation accompanied by grain growth. In the early stage of deformation at relatively low temperature, the adjacent Sm(Co, Fe) 5 and Fe-Co phase formed the Sm 2 (Co, Fe) 17 -H phase, which was stable only with small grain sizes. In the high-temperature deformation stage, the Sm 2 (Co, Fe) 17 -H phase transformed into the Sm 2 (Co, Fe) 17 -R phase with large grain sizes. In addition, the strong c -axis texture formed in the Sm(Co, Fe) 5 phase but not in the Sm 2 (Co, Fe) 17 -R phase. Subsequently, the phase transition process and texture formation mechanism were systematically analyzed by transmission electron microscopy. The initiation of a slip system and/or preferential grain growth explained the formation of texture under the action of uniform stress and strain and assisted by dispersed Sm-rich nanograins. The Sm 2 (Co, Fe) 17 -R grains with poor orientations and large grain sizes did not achieve magnetic hardening, which also damage the magnetic properties. According to the results of this work, we also presented a new strategy to prepare high-performance SmCo-based nanocomposites magnets.

Magnetic and structural properties of nanocomposite permanent magnet produced from crystallization of Pr4Fe67Nb4Cu2Zr1B22 alloy

Present research work narrates synthesis, structural, thermal and magnetic characteristics of Pr4Fe67Nb4Cu2Zr1B22 nanocomposite magnets. Amorphous Pr4Fe67Nb4Cu2Zr1B22 rods were produced through injection casting technique and permanent magnetic characteristics were obtained by one-step annealing the amorphous rods. XRD analysis elucidated that as-cast rods have amorphous phase structure and annealed magnets have tetragonal Pr2Fe14B hard phase, cubic structural α-Fe phase and tetragonal Fe3B soft phase. Optimal annealed magnet composed of 63% Pr2Fe14B hard phase, 26% α-Fe and 11% Fe3B soft phases with mean grain sizes around 51.6 ± 1 nm for Pr2Fe14B, 25.4 ± 2 nm for α-Fe and 21.5 ± 2 nm for Fe3B phases. Microscopic and atomic probe studies showed that the annealed magnet consists of Pr2Fe14B, α-Fe, Fe3B nanosized grains interlinked with thin grain boundaries. Henkel curve evidenced the existence of inter-grain exchange coupling between magnetic nanophase grains. Magnetic hysteresis measurements revealed that Pr4Fe67Nb4Cu2Zr1B22 nanocomposite magnet yielded maximum magnetic characteristics such as coercivity Hc of 382 kA/m, remanence Br of 0.70 T and maximum energy product (BH)max of 64.2 kJ/m3 with rare earth to iron ratio 4:67.

Construction of high performance nanocomposites based on a shape anisotropic soft phase: A micromagnetic simulation study

Nanocomposite permanent magnets are considered as a strong candidate for the next generation of high-performance permanent magnet materials due to their ultra-high theoretical magnetic energy product. In this paper, a nanocomposite theoretical model based on the shape anisotropy of the soft phase (Fe65Co35) is constructed to guide the improvement of coercivity, the lack of which has become a critical problem in improving the performance of Nd-Fe-B nanocomposites further. The results of micromagnetic simulation show that adding a shape anisotropic soft phase to nanocomposites can effectively improve coercivity, delay nucleation during the magnetization reversal process, and help obtain a demagnetization curve with high squareness. When the length size of the soft phase ds ≤ 21 nm and the aspect ratio of the soft phase I = 5 for the Nd2Fe14B/Fe65Co35 nanocomposites, almost square demagnetization curves can be obtained, particularly when ds = 21 nm, the size of the soft phase is 21 × 21 × 105 nm3, the content of the soft phase is 42.1 vol. %, and the Nd2Fe14B/Fe65Co35 nanocomposite achieves a maximum magnetic energy product of 94.4 MGOe. In addition, the results also show that, compared with the cubic nanocomposite model (I = 1), the larger size of the soft phase can be accommodated into the nanocomposites by the addition of shape anisotropy, on the premise of ensuring the soft–hard coupling effect. Our design provides a new strategy and approach for preparing high-performance nanocomposite permanent magnets.

Tripling magnetic energy product in magnetic hard/soft nanocomposite permanent magnets

Nanocomposite materials comprising two or more nanoscale functional components attracted more attention due to their high performance than that of the corresponding single counterpart, which have wide potential applications in many fields. The manipulation of the component phases, fraction/distribution of each phase, and grain size in the nanocomposite is of priority to obtain a high performance. Here, in this work, a two-step process of optimal high-energy ball milling followed by optimal low temperature annealing had been adopted to fabricate Sm–Co/FeCo nanocomposite magnets with triple magnetic energy product in triple-phase nanocomposites. An evolution of microstructure including morphology, phase constitution and grain size towards a high performance magnet had been investigated, which resulted in a record high maximum energy product of 29.1 MGOe. The microstructure of well distributed nanoscale SmCo3 and SmCo5 duplex hard phases and soft phase with almost equal percent is the key factor to get this high performance. The fabrication procedure in controlling the microstructure with uniformly distributed triple phases and nanoscale grain size will shed light on synthesizing other types of nanocomposite materials with high performance.

Micromagnetic simulation for optimizing nanocomposite Nd2Fe14B/[formula omitted]-Fe permanent magnets by changing grain size and volume fraction

Nanocomposite permanent magnets can achieve excellent magnetic properties due to the hardening of a soft phase by hard phase within the length of exchange coupling. The performance of exchange coupling nanocomposite magnets can be optimized through the design of appropriate microstructure by micromagnetic modeling. In this study, we performed a micromagnetic simulation for isotropic exchange coupling nanocomposite Nd2Fe14B/α-Fe permanent magnet in which grain sizes and volume fractions of magnetically hard Nd2Fe14B phase and soft α-Fe phase vary independently, ranging in grain size from 5 nm to 40 nm and in the volume fraction of α-Fe from 10% to 60%. When the grain size of the hard phase is 5 nm, and that of the soft phase is 10 nm, respectively, with the volume fraction of the soft phase of 30%, the highest (BH)max of 197 kJ/m3 can be reached. Furthermore, considering the effects of the grain sizes of the hard and soft phases, we suggest that the grain size of the hard phase plays a more critical role in enhancing maximum energy product (BH)max. The micromagnetic modeling with the variation of grain size and volume faction has been performed with a grain boundary (GB) phase. It was found that when the thickness of the GB phase is very small (~1nm), there is little difference between the simulated results with the GB phase and without GB phase. On the other hand, the coercivities and (BH)max decrease significantly due to the increase of soft phase when the thickness of GB phase is 5 nm.

The effect of Tb doping on the magnetic properties and microstructure of a TbNdFeCoB/Fe7Co3 nanocomposite permanent magnet

Melt-spun NdFeB-type nanocomposite magnetic materials are important in a number of applications, including electromagnetic sensors, magnetic resonance imaging, and voice coil motors. Herein we investigated the magnetic properties and microstructures of melt-spun TbxNd10−xFe80Co4B6/Fe7Co3 (x = 0.1, 0.2, and 0.3) ribbons by means of x-ray diffractometry, scanning electron microscopy, and magnetization experiments. Tb doping resulted in the formation of a 2:14:1 phase with a higher anisotropy field, which suppressed the separation of Fe7Co3 branch crystals and improved the magnetic properties of the material. Optimum magnetic properties that include a remanence (Jr) of 0.62 T, a coercivity (Hci) of 612.0 kA m−1, and a maximum magnetic energy product ((BH)max) of 94.9 kJ m−3 were obtained for the annealed Tb0.3Nd9.7Fe80Co4B6/Fe7Co3 ribbon. Furthermore, the effective anisotropy constant, and the saturation magnetization, in the nanocomposite were determined by the LATS (law of approach to saturation) method. In this study, the values of and were found to lie between those of hard and soft magnetic phases, consistent with the exchange-coupling concept.

A hybrid coercivity mechanism for exchange-coupled nanocomposite permanent magnets

We propose a hybrid coercivity mechanism for exchange-coupled hard/soft multilayers, which incorporates elements of both the traditional nucleation and pinning mechanisms based on both three-dimensional (3D) and one-dimensional (1D) micromagnetic calculations. The magnetic reversal starts with the nucleation of the domain wall near the defects or soft phases, which ends by the pinning usually in the same place. Therefore, pinning near the nucleation centers are the dominant coercivity mechanism for both exchange-coupled nanocomposites and so-called single-phased permanent magnets. Our proposed coercivity mechanism and calculated results agree very well with available experimental data, especially the recently reported high energy products achieved in NdFeB and SmCo based hard/soft multilayers. The hybrid coercivity mechanism can be readily extended to single-phased permanent magnets with defects and other magnetic systems.

High coercivity Pr2Fe14B/α-Fe nanocomposite permanent magnets with Zr addition

The ingots with nominal composition $${ \Pr }_{9.5} {\text{Fe}}_{84 - x} {\text{B}}_{6.4} {\text{P}}_{0.1} {\text{Zr}}_{x}$$ (x = 0, 1, 2, 3) were prepared by an electric arc furnace under purified argon atmosphere. The ribbons were obtained by melt spinning at a wheel speed of 16–33 m·s−1. X-ray diffraction (XRD) results show that P addition decreases crystallinity of hard phase, but further Zr addition increases the amorphous-forming ability of soft phase. The intrinsic coercivity largely increases from 502 (Zr-free) to 945 kA·m−1 (2 at% Zr), which is among the highest value reported so far in this poor rare earth nanocomposite magnets. The hysteresis loops of the alloys with addition of 1 at% and 2 at% Zr show good squareness with single-phase characteristic, indicating well exchange coupling between hard and soft magnetic grains. Transmission electron microscope (TEM) results reveal small grain size and uniformity in the microstructure in the Zr-added samples, which is the reason for high coercivity.

Magnetic properties and reverse magnetization process of anisotropic nanocomposite permanent magnet

Abstract The effects of microstructure parameter upon the magnetic properties of anisotropic nanocomposite permanent magnet (ANPM) Pr2Fe14B/α-Fe were investigated by Micromagnetic finite-element method. The results show that soft magnetic phase filling in the intergranular layer between the hard magnetic phase grains is more favorable for obtaining excellent ANPM Pr2Fe14B/α-Fe. The maximum energy product ((BH)max) of ANPM Pr2Fe14B/α-Fe can reach 762 kJ/m3 for the ideally oriented magnet with the mean grain size of 5 nm and the intergranular layer thickness of 2 nm. The larger (BH)max mainly derives from the contribution of higher remanence which is ascribed to the intergranular exchange coupling between soft and hard magnetic phase. In addition, the reverse magnetization process of ANPM Pr2Fe14B/α-Fe has been studied. It is found that the magnetic moments coherently reverse in reversal magnetization process for ANPM Pr2Fe14B/α-Fe. The study takes the specific composition Pr2Fe14B/α-Fe as an example, however, the results about reasonable microstructure and demagnetization mechanism are still applicable to ANPM with other different hard and soft magnetic phase materials.

Improvement of Magnetic Properties of SmCo5/α-Fe Nanocomposite Magnets by Magnetic Field Annealing

In this paper, magnetic field heat treatment was carried out for the SmCoSUB5/SUB/α-Fe amorphous powders prepared by high-energy ball milling. The effects of annealing temperature and magnetic field on the crystallization, microstructure, and magnetic properties of the SmCoSUB5/SUB/α-Fe nanocomposite permanent magnets were studied. The results show that the magnetic field can benefit the crystallization of SmCoSUB5/SUB phase and the degree of crystallinity of SmCoSUB5/SUB/α-Fe alloy. Thus, the remanence and coercivity of the SmCoSUB5/SUB/α-Fe magnets annealed with magnetic field are significant higher than those of the samples annealed without magnetic field. With the increase of annealing temperature in magnetic field heat treatment, the Sm(Co, Fe)5 phase and FeCo phase are gradually crystallized and grew up, while a small amount of Sm₂CoSUB17/SUB phase appears. The best magnetic properties are MSUBr/SUB = 73.29 emu/g, MSUBr/SUB/MSUBs/SUB = 0.59, and HSUBci/SUB = 6.20 kOe, when the annealing temperature is 700 ℃.

A facile synthesis of anisotropic SmCo5 nanochips with high magnetic performance

Highly anisotropic SmCo5 single crystal particles are promising candidates for high-density data storage and building nanocomposite permanent magnets with large maximum energy product. Previously, nanocrystalline SmCo5 particles obtained by calciothermic reduction exhibit low magnetic energy product due to magnetic isotropy caused by severely agglomerated equiaxial particles. In this study, we report a new strategy to fabricate highly anisotropic SmCo5 nanochips by reductive annealing of precursors with a special designed morphology. The precursors containing single crystal Co(OH)2 nanoflakes and crystalline Sm(OH)3 nanorods were synthesized by a hydrothermal process, and converted into SmCo5 nanochips by subsequent thermal reduction, during which the Co(OH)2 nanoflakes facilitate the formation of SmCo5 nanochips as a template and Sm(OH)3 nanorods help to maintain the hexagonal morphology and single crystal nature. The SmCo5 nanochips exhibit strong magnetic anisotropy and excellent room temperature magnetic properties with a remanence of 7.7 kG, coercivity of 19.3 kOe, and maximum energy product of 14.4 MGOe, which is the highest recorded value for chemical synthesized nanostructured SmCo5 particles.

Application of a novel flash-milling procedure for coercivity development in nanocrystalline MnAl permanent magnet powders

This study shows the possibility of dramatically tuning microstructure and magnetic properties of gas-atomized Mn54Al46 particles by milling for an unprecedented duration of 30 s. This flash-milling procedure avoids the high temperatures typically achieved in lengthy conventional ball milling experiments, and is efficient to reduce the crystallite size to the nanometer scale, induce microstructural strain and ease phase transformations. This leads to the creation of the τ-MnAl phase providing magnetization, and the β-Mn phase operating in the mechanism for coercivity development. Post-annealing at 355 °C for 10 min results in a coercivity about three times larger than that of the annealed starting material, and thus reduces the optimum processing temperature in 75 °C by comparison with that needed for the latter to achieve the best combination of magnetic properties. A maximum obtained coercivity exceeding 5 kOe compares to the highest values reported to date for isotropic MnAl powders attained after milling for times above 20 h. This high coercivity is of additional relevance for further consideration of this material as a hard magnetic phase in the preparation of nanocomposite permanent magnets. The combination of the cost-efficient synthesis technique (gas-atomization) and novel processing route (flash-milling) for the production of low-cost isotropic nanocrystalline MnAl powders, opens new paths to the possible mass production of these materials as an alternative to permanent magnets containing critical raw materials.

A nanocomposite structure in directly cast NdFeB based alloy with low Nd content for potential anisotropic permanent magnets

The magnetic properties of NdFeB magnets can be tailored with different kinds of microstructures. In this work, a nanocomposite structure with amorphous phase remaining inside the micro-sized Nd2Fe14B type grains was observed by Scanning and Transmission Electron Microscopy on the suction cast Nd11Fe60Co10Ti2.5Nb0.5C0.5B15.5 alloy, and then confirmed by various characterization techniques. The worm-like soft magnetic amorphous phases show strong exchange coupling with Nd2Fe14B phase. As a result, the open recoil loops, which are typical characteristics for nanocomposite alloys consisting of hard and soft magnetic phases, have been clearly evidenced. Thus, the formation of this structure may provide an alternative approach to design and fabricate anisotropic nanocomposite NdFeB-based permanent magnets with enhanced magnetic properties.

Fabrication of bulk nanostructured permanent magnets with high energy density: challenges and approaches.

Nanostructured permanent magnetic materials, including exchange-coupled nanocomposite permanent magnets, are considered as the next generation of high-strength magnets for future applications in energy-saving and renewable energy technologies. However, fabrication of bulk nanostructured magnets remains very challenging because conventional compaction and sintering techniques cannot be used for nanostructured bulk material processing. In this paper we review recent efforts at producing bulk nanostructured single-phase and composite magnetic materials with emphasis on grain size control, anisotropy generation and interface modification.