Open AccessArticle

Investigation of the Impact of SmFeN Doping on the Anisotropic NdFeB/SmFeN Composite Magnets

Wei Cai

^1,*

Xinqi Zhang

Zhiping Shi

^2,3,

Haibo Chen

^2,3

Qiaomin Zhu

^1,4,

Kun Jiang

^2,3,

Liang Qiao

Yao Ying

¹,

Wangchang Li

¹,

Jing Yu

¹,

Juan Li

Jingwu Zheng

and

Shenglei Che

Research Center of Magnetic and Electronic Materials, College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China

Hangzhou Chase Magnetics Co., Ltd., Hangzhou 311200, China

Hangzhou Chase Technology Co., Ltd., Hangzhou 311200, China

⁴

Songyang No. 1 Middle School, Lishui 323400, China

Author to whom correspondence should be addressed.

J. Compos. Sci. 2024, 8(12), 514; https://doi.org/10.3390/jcs8120514

Submission received: 18 October 2024 / Revised: 23 November 2024 / Accepted: 3 December 2024 / Published: 6 December 2024

(This article belongs to the Special Issue Metal Composites, Volume II)

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Abstract

By incorporating various types of permanent magnetic powders, composite magnets with cost-effectiveness and a wide range of magnetic properties can be achieved. In this study, the anisotropic composite magnets were fabricated using the hot press forming method, which involved blending neodymium iron boron (NdFeB) powder and samarium iron nitrogen (SmFeN) powder. The experiment demonstrated that the magnet density reaches its maximum point when the doping level of SmFeN reaches 20 wt.%, aligning remarkably well with the corresponding theoretical value of 19.22 wt.% achieved through a cubic stacking arrangement. In the absence of an applied magnetic field or under a sufficiently high oriented magnetic field (3 T), the remanence variation pattern in composite magnets doped with different amounts of SmFeN aligns consistently with the density pattern, yielding a maximum value of 20%. However, in the actual solidification process, the orientation field is insufficient (e.g., 1.5 T), necessitating a doping amount that exceeds the value corresponding to peak density by 28% to achieve optimal remanence. This observation suggests that the incorporation of a higher proportion of small-sized and relatively low coercivity SmFeN magnetic powder can effectively facilitate the rotational alignment of neighboring large-sized NdFeB magnetic powder under weak magnetic fields, thereby inducing a synergistic effect.

Keywords:

anisotropy; HDDR-NdFeB; Sm₂Fe₁₇N₃; doping; magnetic size gradation

1. Introduction

With the rapid development of new energy vehicles and other industries, the application of magnetic devices is increasingly miniaturized and lightweight, which can effectively reduce energy loss and improve utilization [1,2,3]. In the field of motor applications, bonded neodymium iron boron (NdFeB) can interact with the coil to generate mechanical energy or electrical energy to drive the system to operate and work, and it is one of the important magnetic functional materials in modern industrial production [4,5,6,7]. Bonded NdFeB can be divided into isotropic and anisotropic. Compared with isotropic bonded NdFeB devices, anisotropic bonded NdFeB devices after orientation have better performance and can provide stronger magnetic properties, so the research on anisotropic bonded NdFeB has been attracting much attention [8,9,10].

In order to attain a wide range of magnetic properties and enhance cost-effectiveness, composite magnets are commonly fabricated through the blending and doping of various types of magnetic powders using processing techniques such as injection molding or hot-pressing. Yue et al. [11] employed a calendering molding technique to fabricate flexible NdFeB/SmFeN composite rubber magnets with high loading and magnetic anisotropy. The investigation demonstrated that the pure NdFeB material exhibited limitations in achieving complete sheet formation, whereas the incorporation of 1% fine SmFeN powder enabled the successful fabrication of fully formed sheets exhibiting excellent flexibility. The anisotropic NdFeB magnetic powder utilized for magnet bonding is typically obtained via the hydrogenation-disproportionation-desorption-recombination (HDDR) process. However, it has been observed that optimal magnetic performance is achieved when the average particle size falls within the range of 80–100 μm. Research findings suggest that further refinement of the magnetic powder leads to a deterioration in its magnetic properties. The compression and fusion of magnetic powder particles with a large particle size inevitably result in interparticle gaps, leading to a reduction in the packing density of the magnetic powder. Consequently, this diminishes the remanence of the magnet and potentially lowers its degree of orientation [12,13,14]. However, the performance of samarium iron nitrogen (SmFeN) magnetic powder actually improves as the particle size decreases, while exhibiting similar Hcj and BHm values to anisotropic NdFeB magnets. In order to strike a balance between oxidation resistance and magnetic properties, it is generally recommended to control the average particle size of samarium iron nitride magnets within the range of 1–5 μm. Therefore, doping NdFeB with SmFeN magnetic powder featuring significantly disparate particle sizes can effectively fill the voids created by larger particles using smaller ones, thereby enhancing the density and corresponding magnetic properties of the composite magnet [15,16,17,18,19]. Currently, the influence of doping quantity on the density or magnetic performance of magnet powders with varying particle sizes is commonly inferred from an abundance of experimental data, lacking theoretical indicators for the gradation law of magnet powders. Concurrently, in the process of anisotropic magnet powder formation, magnetic orientation assumes a crucial role. Furthermore, it is worthwhile to investigate potential coupling effects between adjacent magnet powders when blending different types together during magnetic orientation.

In order to further enhance the magnetic properties of anisotropic bonded NdFeB, this study investigates composite magnets consisting of anisotropic NdFeB/SmFeN with varying particle size distributions. The optimal stacking method for magnetic powder was determined through finite element simulation, and the principles of particle size gradations in different magnetic powders were analyzed to calculate the optimal filling density of anisotropic NdFeB/SmFeN composite magnets. Anisotropic NdFeB/SmFeN composite magnets with varying grading ratios were fabricated using the magnetic field temperature and pressure method. Experimental tests were conducted to investigate the influence of different grading ratios on the density, remanence, coercivity, and maximum energy product of these anisotropic NdFeB/SmFeN composite magnets. The distribution relationship between different levels of anisotropic SmFeN content and the degree of magnet orientation was investigated to elucidate the role played by anisotropic SmFeN magnetic powder during the process of magnet orientation.

2. Experiment

The anisotropic Nd-Fe-B magnetic powder prepared by HDDR process and refined by ball milling was obtained from Grinm Advanced Materials Co., Ltd (Beijing, China). The chemical composition is as follows: Nd 29.5 wt.%, Fe 68.6 wt.%, and B 1.0 wt.%, while others accounted for 0.9 wt.%. The anisotropic Sm-Fe-N magnetic powder prepared by the REDOX process and refined by ball milling is from Jiangxi Joins New Materials Co., LTD (Jiangxi, China). The chemical composition is as follows: Sm 24.3 wt.%, Fe 71.2 wt.%, and N 4.5 wt.%, while others accounted for 1 wt.%. 0–100 wt.% anisotropic SmFeN magnetic powder was added into the anisotropic NdFeB magnetic powder, and 2.5 wt.% epoxy resin and 0.5% coupling agent were dissolved into acetone solution. After the acetone volatilized, the lumpy bonded magnetic powder was ground and stirred for more than 10 min. The principle of anisotropic NdFeB/SmFeN composite magnet pressing is shown in Figure 1. Anisotropic NdFeB/SmFeN composite magnet was pressed and formed based on the hot-pressing method. A heating rod was used to preheat the Φ 10 × 10 pressing mold. The mold temperature was set at 120 °C, and a thermocouple was used to detect the mold temperature. The orientation coil generates an orientation magnetic field parallel to the pressure direction, with magnitudes of 0.8 T, 1.5 T, and 3 T under a constant current field. In comparison, when the orientation coil is inactive, the orientation magnetic field becomes negligible at 0 T.

After the cross-section of anisotropic NdFeB/SmFeN composite magnets prepared by hot-pressing was polished with sandpaper, the microstructure was observed using a scanning electron microscope (SEM, Hitachi-SU1050, Tokyo, Japan). The residual induction (Br), coercive force (Hc), and maximum magnetic energy product (BH(max)) of the magnet were determined by the permanent magnet precision measurement system (NIM-6200C, NIM, Beijing, China), and the magnetic powder properties were determined by the vibrating sample magnetometer (VSM, Lakeshore-8600, Lake Shore Cryotronics, Inc., Westerville, OH, US). The particle size distribution was determined by a laser particle size analyzer (Sympatec GmbH-HELOS, Sympatec, Clausthal-Zellerfeld, Germany ), and the magnet density was determined by a density electronic balance (Instrument -AE323J, Sunny Hengping, Shanghai, China).

3. Results and Discussion

3.1. Theoretical Packing Mode and Filling Rate of Magnetic Particles with Optimal Magnetic Properties

The microstructure images and corresponding particle size distributions of two types of magnetic powders are depicted in Figure 2. It can be observed from the figures that HDDR-NdFeB powder exhibits a relatively regular morphology with an average particle size (D50) of 101.07 μm, while SmFeN powder displays irregular polyhedral shapes with an average particle size of around 2 μm. The magnetic properties and density of these powders are further characterized in Table 1. According to Table 1, the intrinsic coercivity of anisotropic NdFeB powder is approximately 20% higher than that of anisotropic SmFeN powder; however, both powders exhibit comparable remanence and magnet density. The findings suggest that the non-linear variations in density and remanence of composite magnets composed of anisotropic NdFeB/SmFeN are primarily influenced by doping amount rather than inherent differences in the magnetic powders themselves.

The anisotropic NdFeB magnetic powder exhibits an average particle size distribution of approximately 100 μm, resulting in certain gaps between adjacent particles and a corresponding level of porosity during compression. The incorporation of anisotropic SmFeN magnetic powder with an average particle size distribution of 2 μm can effectively fill these gaps, thereby improving the magnetic performance of the NdFeB/SmFeN magnet through this grading principle.

Common methods for stacking magnetic powders include simple cubic, body-centered cubic, and hexagonal stacking. To determine the stacking model that achieves the maximum filling rate of anisotropic NdFeB magnetic powder in different directions and maximizes its magnetic performance, anisotropic SmFeN magnetic powder will be used to fill the gaps between anisotropic NdFeB magnetic powders. A simulation method will be employed to compare the magnetic performance under different stacking methods, as illustrated in Figure 3.

Due to the different structures of the anisotropic Nd-Fe-B magnetic particle stacking modes, the magnetic properties of the different anisotropic Nd-Fe-B magnetic powder stacking modes are simulated and analyzed under the same volume for reliability of comparison. The anisotropic Nd-Fe-B magnetic powder stacking modes have the same particle size, magnetization mode, and magnetic powder properties. The simulated distribution of the magnetic field is illustrated in Figure 4. During the modeling process, the following assumptions were made: (1) The three groups of models were fully oriented along the axial direction and saturated with magnetization; (2) the magnetic properties of NdFeB listed in Table 1 were selected for the magnetic powder; (3) magnetic force interaction between adjacent magnetic powder particles was considered throughout the entire magnet; and (4) Zero Tangential H-Field boundary conditions were set, and an appropriate boundary size was chosen after verifying its influence on the distribution of the magnetic field.

The surface magnetic properties of the anisotropic Nd-Fe-B magnetic particles of the above three different stacking modes were simulated and analyzed respectively according to the performance parameters in Table 1, and the magnetic properties of Φ 10 × 10 cylindrical end face at the central position were compared. It was observed that the simple cubic stacking method exhibited the lowest magnetic performance, followed by body-centered cubic stacking, while hexagonal close-packed stacking demonstrated the highest performance. In comparison to the reference simple cubic stacking, body-centered cubic stacking showed a 1.31 times higher magnetic performance, whereas hexagonal close-packed stacking displayed a 1.4 times higher performance. The effective utilization of the magnetic field at the particle gaps can be achieved by strategically arranging magnetic powder and increasing the filling rate, thereby enhancing magnetism in magnets. As depicted in Figure 4, both simple cubic and body-centered cubic stackings generated reverse magnetic fields at gaps (indicated by black boxes) due to characteristics such as lower filling rate and specific particle arrangement, resulting in weakened magnetism of magnets. Conversely, the hexagonal close-packed stacking, characterized by its unique particle arrangement and higher filling rate, does not exhibit significant reverse fields at gaps, thereby enhancing magnetism efficiency.

The hexagonal stacking method demonstrates the highest space utilization rate through the simulation and emulation of various stacking methods. Consequently, the optimal ratio of anisotropic NdFeB/SmFeN magnetic particle grading is investigated. The following assumptions are made for the anisotropic NdFeB/SmFeN magnetic particle grading:

(1): Anisotropic NdFeB magnetic powder and anisotropic SmFeN magnetic powder have good sphericity;
(2): The anisotropic NdFeB/SmFeN composite magnet does not deform; and
(3): The influence of magnetic particle agglomeration is not considered.

According to the densest stacking method, Figure 5a illustrates the arrangement of anisotropic NdFeB magnetic powder in an A–B–A–B pattern. The densest stacking mode depicted in Figure 5a has been simplified, and the corresponding simplified model is presented in Figure 5b, where the spheres represent the centroids of anisotropic NdFeB magnetic powder particles. The regular tetrahedron, as depicted in Figure 5c, is composed of an intermediate layer consisting of anisotropic NdFeB magnetic powder and adjacent particles from either the upper or lower layers.

The analysis of Figure 5 reveals that the optimal stacking arrangement for anisotropic NdFeB magnetic powder exhibits a regular hexahedral structure with maximum density. Assuming the radius of each particle as R (μm) and the side length of the regular hexahedron as 2R, our objective is to analytically determine the filling efficiency of anisotropic NdFeB magnetic powder.

According to the geometric relationship, the following expression is satisfied:

\{\begin{matrix} \frac{a}{s i n 30 °} = \frac{R}{s i n 60 °} = \frac{b}{s i n 90 °} \\ b^{2} + {(H / 2)}^{2} = {(2 R)}^{2} \end{matrix}

(1)

where a (μm) is the distance between the center of mass of the three magnetic particles in layer A and the midpoint of the two magnetic particles; b (μm) is the distance from the center of mass of the three magnetic particles in layer A to the center of the magnetic powder; H (μm) is the center distance between layer A and layer A magnetic particles.

H can be obtained:

H = \frac{4}{3} \sqrt{6} R

(2)

Combined with Figure 5b, the filling rate of anisotropic NdFeB magnetic powder δ (%) can be obtained:

δ = \frac{V_{p o w d e r}}{V_{c u b e}} = \frac{3 \times \frac{4}{3} π R^{3} + 2 \times \frac{1}{2} \times \frac{4}{3} π R^{3} + 12 \times \frac{1}{6} \times \frac{4}{3} π R^{3}}{\frac{1}{2} \times 6 \times 2 R \times \sqrt{3} R \times H}

(3)

The theoretical calculation of the densest packing mode for anisotropic Nd-Fe-B magnetic powder indicates a maximum filling rate of 74.05%. Consequently, the dopant ratio (1 − δ) for anisotropic SmFeN magnetic powder is determined to be 25.95%. When two powders with similar densities are present, the volume filling rate can also be referred to as the weight increase rate. During the doping process, anisotropic SmFeN magnetic powder also encounters the challenge of porosity. When it meets the hexagonal packing mode, the theoretical content n (%) of the maximum filling density anisotropic SmFeN magnetic powder is calculated as 19.22% using the following equation:

n = (1 - δ) \times δ

(4)

3.2. Analysis of Magnetic Properties of Composite Magnets Under Different Doping Ratios

To verify the doping amount of SmFeN powder in composite magnets, which demonstrate optimal magnetic properties and maximum filling density as predicted by theoretical simulations, we utilized varying ratios of anisotropic NdFeB and SmFeN powders. The fabrication process involved hot-pressing to create anisotropic NdFeB/SmFeN composite magnets. The cross-sectional morphology was examined, while parameters, including density, remanence, coercivity, and maximum magnetic energy product, were individually measured. The microscopic structure and corresponding density variation of NdFeB/SmFeN composite magnets with different particle size ratios are illustrated in Figure 6. The figure clearly illustrates the distinctive characteristics of the distribution of magnetic powders with varying particle sizes. The density change curve exhibits an initial increase followed by a subsequent decrease in the density of NdFeB/SmFeN composite magnets. This can be attributed to the presence of gaps between large particles when SmFeN content is absent (0%), indicating a composition solely comprised of anisotropic NdFeB powder. Conversely, as SmFeN content reaches 100%, there is an exponential rise in friction resistance and magnetic repulsion among small particles, thereby enhancing their resistance to molding pressure. Consequently, under identical pressure conditions, achieving higher density becomes challenging, as evidenced by observed gaps at larger magnification rates during morphology observation. The maximum filling rate of a composite magnet can only be achieved when an appropriate quantity of anisotropic SmFeN powder fills the interstitial spaces without causing separation among large NdFeB particles. The highest density value for anisotropic SmFeN occurs at approximately 20% doping amount, as depicted in Figure 6h, which aligns with theoretical simulations aimed at achieving optimal filling rate through samarium iron nitride doping.

In the process of fabricating composite magnets, different oriented magnetic fields are achieved by adjusting the voltage. Subsequently, composite magnets are formed through hot-pressing molding using varying proportions of anisotropic NdFeB and SmFeN magnetic powders under these distinct oriented magnetic fields. The relationship between the doping ratio of SmFeN and the orientation field is depicted in Figure 7, showcasing its impact on the corresponding variation in magnetic properties of the composite magnet. In this figure, it is evident that as the content of anisotropic SmFeN doping increases, there is a gradual reduction in coercivity for anisotropic NdFeB/SmFeN composite magnets. This can be attributed to the lower coercivity exhibited by anisotropic SmFeN powder compared to anisotropic NdFeB powder, resulting in a decrease in overall magnet coercivity. However, this rate of decrease varies depending on the amount of SmFeN doping. Within a doping range up to 30%, it decreases at a slower pace; beyond this threshold, it rapidly declines and demonstrates a linear symmetric correlation with samarium iron nitride doping amount. The findings suggest that the predominant influence on achieving orientation is primarily attributed to NdFeB powder at lower doping levels, while it shifts towards a greater reliance on SmFeN powder at higher concentrations. The residual magnetization and maximum energy product of anisotropic NdFeB/SmFeN composite magnets exhibit a similar trend in density variation as the doping amount of samarium iron nitride, i.e., they initially increase and then decrease. However, the optimal doping amount for achieving the highest residual value and density in different orientation magnetic fields varies. In the absence or presence of a high orientation magnetic field (3 T), the highest density and residual magnetization are observed at approximately 20% SmFeN doping content, as depicted in Figure 7a,b,g,h. Harshida Parmar et al. [20] also observed the presence of small SmFeN particles (3 μm) filling the gaps between larger NdFeB particles (105 μm), thereby increasing the packing density and enhancing the magnetic performance of the composite magnet. Conversely, when there is an insufficiently high orientation magnetic field (1.5 T, 0.8 T), the highest residual magnetization occurs at around 28% SmFeN doping content, as shown in Figure 7c–f. The residual magnetization exhibits positive correlation with both density and degree of orientation. The density becomes the predominant factor influencing residual magnetization in situations where there is no orientation or under fully oriented saturation conditions due to the absence or presence of high orientation magnetic fields, respectively. The presence of insufficiently high orientation magnetic fields leads to varying degrees of orientation for different doping amounts. As a result, both the density and degree of orientation have dual effects on residual magnetization in composite magnets with varying dopant concentrations. Considering practical production constraints, where maintaining a consistently high level of orienting magnetic field often leads to excessive coil area or coil heating issues over time, it may not be operationally feasible to use a 3 T orienting magnetic field; therefore, during production processes, only an orienting magnetic field similar to about 1.5 T can be utilized instead.

The squareness of the demagnetization curve gradually increases with an increase in SmFeN content, as depicted in Figure 8 for an orientation magnetic field of 0.8 T. However, when the SmFeN content reaches 20%, the coercive force of composite magnets remains nearly constant under varying orientation magnetic fields, while the remanence exhibits a positive correlation with increasing orientation field strength, indicating a significant enhancement in the squareness of the demagnetization curve. Squareness refers to the ratio of coercivity to intrinsic coercivity at 0.9 Br on the demagnetization curve, with a higher ratio indicating enhanced magnet stability under dynamic working conditions. The increased SmFeN content contributes to improved magnet stability, potentially attributed to smaller particles of SmFeN filling gaps between larger NdFeB particles and the reducing demagnetizing field effects caused by these gaps.

Under the action of the orientation magnetic field, the magnetic particles of the anisotropic NdFeB/SmFeN composite magnet are arranged in an orderly manner along the direction of the magnetic field. The ratio of the actual remanence B_r to the theoretical remanence B_r^* of the anisotropic NdFeB/SmFeN composite magnet under the action of magnetic field orientation is taken as f, as shown in Formula (5).

f = \frac{B_{r}}{B_{r}^{*}}

(5)

The orientation degree of various anisotropic NdFeB/SmFeN composite magnets is computed based on Formula (5), and the distribution of orientation degrees is illustrated in Figure 8d.

In Figure 8d, it can be observed that the degree of anisotropy in NdFeB/SmFeN composite magnets fluctuates slightly under a 3 T applied magnetic field with increasing doping amount of anisotropic SmFeN. However, under 1.5 T and 0.8 T applied magnetic fields, the degree of anisotropy exhibits a trend of initially increasing and then decreasing. This is attributed to the displacement of internal magnetic domain walls and particle rotation in the magnetic powder during the orientation process of anisotropic NdFeB/SmFeN composite magnets. The average particle size of anisotropic NdFeB powder is approximately 100 μm, with a multi-domain structure consisting mainly of fine grains, resulting in higher resistance to the displacement and rotation of domain walls. According to the previous discussion, the orientation of composite magnets is primarily determined by NdFeB magnetic powder at low doping levels and by SmFeN magnetic powder at high doping levels. The addition of an appropriate amount of anisotropic SmFeN magnetic powder effectively fills the gaps between particles of anisotropic NdFeB magnetic powder and provides a coating effect on them. The pre-oriented anisotropic SmFeN magnetic powder assists in orienting adjacent anisotropic NdFeB magnetic powder particles under the influence of the orientation field, thereby enhancing the exchange coupling effect and improving the degree of orientation in the NdFeB/SmFeN composite magnet. Luo et al. [21] also proposed that the small SmFeN particles, which are clustered around the central NdFeB powder, exhibit a preferential magnetization behavior under low magnetic fields. This results in the formation of an additional bias magnetic field (HB). When combined with the externally applied magnetic field, this additional bias magnetic field facilitates the rotation of NdFeB. However, under a high orientation field that can sufficiently orient NdFeB, the assisting effect of anisotropic SmFeN magnetic powder becomes less significant. At 1.5 T and 0.8 T orientation fields, maximum orientation occurs when approximately 30% of anisotropic SmFeN is doped into it. This indicates that under a low orientation field where there isn’t enough force for effective reorientation movement of larger-sized anisotropic NdFeB particles, adding anisotropic SmFeN can effectively promote their reorientation due to its lubricating effect on them. The maximum energy product of the NdFeB/SmFeN composite magnet occurs when about 28% doping level of anisotropic SmFeN matches with its maximum degree of orientation value, which verifies that there is a correlation between magnet performance and orientational characteristics in different orientation fields for this type of composite magnet.

4. Conclusions

Composite magnets comprising anisotropic NdFeB and SmFeN powders with varying particle sizes were prepared using different oriented magnetic fields and grading ratios, based on the principle of magnetic powder grading. Subsequently, a comprehensive performance analysis was conducted on these magnets, leading to the following conclusions:

(1): Utilizing various stacking methods of magnetic powder, the simulation technique was employed to determine that hexagonal stacking yields the highest magnetic performance and filling density for magnets. The optimal doping amount of anisotropic SmFeN powder is theoretically determined to be 19.22 wt.%. The experimental findings demonstrate that the density of composite magnets initially increases and then decreases as the doping amount of SmFeN powder is increased. When the doping amount reaches 20%, the density of composite magnets reaches its peak, aligning with the calculated theoretical value.
(2): With the increase in anisotropic SmFeN magnetic powder content, the coercivity of anisotropic NdFeB/SmFeN composite magnets gradually decreases, while the remanence and maximum energy product initially increase and then decrease. However, achieving the highest residual magnetization and maximum density in anisotropic NdFeB/SmFeN composite magnets requires different doping amounts for different orientation fields. In the absence of an orientation field or with a sufficiently high orientation field (3 T), the highest residual magnetization occurs at a SmFeN doping content of 20%. Conversely, with insufficiently high orientation fields (1.5 T, 0.8 T), the highest residual magnetization occurs at a SmFeN doping content of 28%. This indicates that increasing the amount of smaller-sized and relatively low-coercivity SmFeN dopants can effectively promote the orientational rotation of adjacent large-grain NdFeB magnetic powders under low magnetic fields to exert exchange coupling effects. However, excessive SmFeN powder doping increases frictional resistance and magnetic repulsion between small particles adjacent to each other under compressive force, which affects powder rotation. Therefore, under 1.5 T and 0.8 T orientation fields, composite magnets exhibit their highest degree of anisotropy when doped with 28% SmFeN.

Author Contributions

Conceptualization, W.C.; data curation, W.C.; formal analysis, Z.S.; funding acquisition, H.C., L.Q., J.Z. and S.C.; investigation, X.Z., Q.Z. and K.J.; methodology, X.Z., Q.Z. and K.J.; project administration, W.C. and H.C.; resources, W.C.; software, Q.Z. and K.J.; supervision, W.C.; validation, Q.Z. and K.J.; visualization, X.Z. and Z.S.; writing—original draft, X.Z. and Z.S.; writing—review and editing, W.C., H.C., Y.Y., W.L., J.Y. and J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (52101235), the basic public welfare re-search program of Zhejiang Province (LGG22E010010), the “Pioneer” and “Leading Goose” R&D Program of Zhejiang (2024C01146), the Intergovernmental International Science, Technology, and Innovation Cooperation Key Project of the National Key R&D Programme (No. 2022YFE0109800), and the National Key Research and Development Program of China (2021YFB3500203).

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

Authors Zhiping Shi, Haibo Chen and Kun Jiang were employed by Hangzhou Chase Magnetics Co., Ltd. and Hangzhou Chase Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. Pressing principle of anisotropic NdFeB/SmFeN composite magnet: (1) orientation coil; (2) thermocouple; (3) composite magnet; (4) indenter; (5) press the mold.

Figure 2. Characterization of morphology and corresponding particle size distribution in anisotropic NdFeB (a,c) and anisotropic SmFeN (b,d) magnetic powders.

Figure 3. Different stacking modes of anisotropic Nd-Fe-B magnetic particles: (a) simple cubic stacking; (b) body-centered cubic packing; (c) hexagonal packing.

Figure 4. Magnetic field distribution of anisotropic NdFeB magnetic particles under different stacking modes: (a) simple cubic stacking; (b) body-centred cubic packing; (c) hexagonal packing.

Figure 5. Anisotropic Nd-Fe-B magnetic powder densest stacking: (a) physical model; (b) simplified model; (c) analytical model.

Figure 6. The microscopic structure of NdFeB/SmFeN composite magnets with different SmFeN content: (a) 0%; (b) 20%; (c) 28%; (d) 40%; (e) 60%; (f) 80%; (g) 100%; and the density variation curves (h).

Figure 7. Magnetic properties of anisotropic NdFeB/SmFeN composite magnets at different proportions: (a,b) 3 T oriented magnetic field; (c,d) 1.5 T oriented magnetic field; (e,f) 0.8 T oriented magnetic field; (g,h) non-oriented magnetic field.

Figure 8. The demagnetization curves (a) at 0.8 T orientation magnetic field and squareness ratio (b) of NdFeB/SmFeN composite magnets with varying SmFeN contents were analyzed, along with the demagnetization curves (c) and orientation degrees (d) under different orientation magnetic fields.

Table 1. Anisotropic NdFeB/SmFeN magnetic particle properties.

Magnetic Powder	B_r (T)	H_cj (KOe)	(BH)_max (MGOe)	Density (ρ) (g/cm³)
Nd-Fe-B	1.36	12.7	41	7.6
Sm-Fe-N	1.32	10.3	38.2	7.6

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MDPI and ACS Style

Cai, W.; Zhang, X.; Shi, Z.; Chen, H.; Zhu, Q.; Jiang, K.; Qiao, L.; Ying, Y.; Li, W.; Yu, J.; et al. Investigation of the Impact of SmFeN Doping on the Anisotropic NdFeB/SmFeN Composite Magnets. J. Compos. Sci. 2024, 8, 514. https://doi.org/10.3390/jcs8120514

AMA Style

Cai W, Zhang X, Shi Z, Chen H, Zhu Q, Jiang K, Qiao L, Ying Y, Li W, Yu J, et al. Investigation of the Impact of SmFeN Doping on the Anisotropic NdFeB/SmFeN Composite Magnets. Journal of Composites Science. 2024; 8(12):514. https://doi.org/10.3390/jcs8120514

Chicago/Turabian Style

Cai, Wei, Xinqi Zhang, Zhiping Shi, Haibo Chen, Qiaomin Zhu, Kun Jiang, Liang Qiao, Yao Ying, Wangchang Li, Jing Yu, and et al. 2024. "Investigation of the Impact of SmFeN Doping on the Anisotropic NdFeB/SmFeN Composite Magnets" Journal of Composites Science 8, no. 12: 514. https://doi.org/10.3390/jcs8120514

APA Style

Cai, W., Zhang, X., Shi, Z., Chen, H., Zhu, Q., Jiang, K., Qiao, L., Ying, Y., Li, W., Yu, J., Li, J., Zheng, J., & Che, S. (2024). Investigation of the Impact of SmFeN Doping on the Anisotropic NdFeB/SmFeN Composite Magnets. Journal of Composites Science, 8(12), 514. https://doi.org/10.3390/jcs8120514

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