Improving the Soft Magnetic Characteristics of Nanocrystalline Soft Magnetic Composites Through the Incorporation of Ultrafine FeSiAl Powders

Abstract

Nanocrystalline powders, characterized by a biphasic amorphous nanocrystalline structure, demonstrate outstanding soft magnetic characteristics, including reduced coercivity (H_c), enhanced effective permeability (μ_e), and increased resistivity. However, their high hardness, poor formability, and significant core loss (P_cv) restrict their use in high-performance molded inductors. In this study, FeSiBCuNb/FeSiAl nanocrystalline soft magnetic composites (NSMCs) were fabricated, and the influence of varying the FeSiAl concentration on the microstructure, density, and soft magnetic characteristics of NSMCs was investigated. Then, the underlying mechanisms of these effects were explained. The results demonstrate that FeSiAl exhibits apparent deformation following compression, effectively filling the air gap between the FeSiBCuNb powder particles, thereby enhancing coupling among the magnetic particles. Consequently, the density of the NSMCs was enhanced, leading to a significant improvement in their overall soft magnetic properties. When 50 wt.% FeSiAl is added, the NSMCs display outstanding magnetic properties, including a low H_c of 4.36 Oe, a high μ_e of 48.7, a low P_cv of 119.35 kW/m³ at 50 mT and 100 kHz, and a high DC-bias performance of 73.29% at 100 Oe. Compared to NSMCs without FeSiAl, μ_e increased by 59.4% and P_cv decreased by 66.1%. Meanwhile, the incorporation of ultrafine FeSiAl powder was found to significantly improve the material properties, as the deformable FeSiAl particles effectively fill interparticle gaps during compaction, enhancing density and magnetic coupling. The 50 wt.% FeSiAl composition demonstrated exceptional properties. These advances address critical challenges in high-frequency power electronic applications and provide a practical material solution for next-generation power electronics.

1. Introduction

Soft magnetic composites (SMCs) are crucial magnetic components of power electronics and electrical systems. These materials are primarily used for energy conversion, filtering, and electromagnetic interference suppression [1,2]. The advent of third-generation semiconductors, including gallium nitride and silicon carbide, has facilitated the development of power electronic components, such as molded inductors. To achieve miniaturization, enhanced efficiency, and higher operating frequencies, more stringent demands have been placed on the high-frequency performance of SMCs [3,4]. The nanocrystalline powder features a distinctive biphasic structure that combines the amorphous and nanocrystalline phases. This unique composition endows it with superior soft magnetic properties, including a low H_c, a high μ_e, and high resistivity. As a result, it is considered an ideal material for high-frequency applications [5,6]. However, compared to traditional soft magnetic metal powders, nanocrystalline powders have high hardness, poor formability, and high loss, which limit their application in high-performance inductors [7,8]. For molded inductors, the unique internal structure of the copper wire windings prevents these components from withstanding high-pressure molding or high-temperature annealing processes [9,10]. Therefore, further improvement in the compressibility and permeability of NSMCs and loss reduction are necessary to optimize their comprehensive soft magnetic properties.

The use of lubricants, characterized by strong adhesive properties and good flow characteristics, promotes the reorganization of powder particles and improves the molding of magnetic powders. Consequently, this reduces the air-gap density and residual stresses, yielding outstanding soft magnetic performance in SMCs. Nevertheless, excessive non-magnetic lubricant between magnetic particles may decrease the permeability and saturation magnetization (M_s). One effective way to improve the compressibility of hard powders is to mix multiple small, softer metal magnetic particles to obtain composite materials [11]. Several researchers have effectively achieved targeted performance results by selecting suitable soft magnetic powders, refining the preparation methods, and altering the microstructure. For example, Li et al. [12] improved the permeability and reduced P_cv by incorporating FeNi into FeSiB powder. Zhang et al. [13] successfully enhanced the magnetic flux density (B_s) and DC-bias performance of FeSiBPNbCr amorphous SMCs by introducing FeCo powder. Chen et al. [14] explored the influence of Permalloy incorporation on the soft magnetic characteristics of Fe_83.5Si_7.5B₅Cr₄ amorphous nanocrystalline powders, revealing a notable enhancement in performance, mainly reflected in the significant increase in μ_e and substantial reduction in P_cv. Tian et al. [15] developed FeSiBNbCu/SiO₂ SMCs featuring a core-shell architecture. The study revealed that numerous submicron-sized SiO₂ particles are evenly distributed across the powder surfaces, thereby substantially enhancing the insulation capabilities. As a result, these SMCs demonstrate a high μ_e of 84 and a P_cv of 174 kW/m³ at 50 kHz, with Bm = 0.1 T. Zhang et al. [16] prepared the FeSiBCuNb/NiCuZnFe₂O₄ core–shell structure. Their results showed that the prepared NiCuZnFe₂O₄ was evenly coated on the surface of FeSiBCuNb powder, forming a fine insulating layer and exhibiting excellent magnetic properties. Wang et al. [17] analyzed the influence of the addition of carbonyl iron powder (CIP) on the magnetic characteristics of FeSiBCuNb/CIP composite cores. Their findings revealed that adding an optimal amount of CIP enhances the magnetic performance of the composites, achieving a maximum μ_e of 35.3, a minimum H_c of 23.34 A/m, and the lowest P_cv of 281.87 mW/cm³ at 50 mT and 100 kHz. In our previous study [18], we developed FeSiBCuNb/FeNi NSMCs by incorporating 50 wt.% FeNi powder, which was converted into FeSiBCuNb nanocrystalline powder, and the mixture was compacted into cores. This method led to substantial improvements, achieving an µ_e of 59.3, a DC-bias performance of 65.6% at 100 Oe, and a P_cv of 99.8 kW/m³ under 50 mT/100 kHz. These enhancements were attributed to the FeNi particles filling interstitial voids, thereby improving the soft magnetic performance of NSMCs. Despite considerable progress in preparing Fe-based nanocrystalline materials, developing SMCs with outstanding high-frequency efficiency, enhanced permeability, strong saturation magnetization, and reliable DC-bias behavior still presents a significant challenge.

As a conventional soft magnetic material, FeSiAl has the advantages of low cost, low high-frequency loss, and good thermal stability, particularly in high-frequency inductors, transformers, and electromagnetic shielding [19,20]. This work involved the fabrication of NSMCs through cold pressing, using a combination of nanocrystalline FeSiBCuNb powder and FeSiAl. The influence of different FeSiAl mass ratios was systematically examined, focusing on their effects on microstructure, density, static magnetic properties, permeability, core loss, and DC-bias behavior. The findings indicate that the electromagnetic properties of NSMCs can be substantially improved by incorporating an optimal amount of FeSiAl, and the underlying physical mechanism was studied systematically.

2. Experimental Details

2.1. Preparation of FeSiBCuNb/FeSiAl NSMCs

The FeSiBCuNb nanocrystalline powder utilized in this study, which has a nominal composition of Fe_73.5Si_13.5B₉Cu₁Nb₃ and was produced using commercial gas–water atomization, was provided by Epson Atmix Corporation (Hirosaki, Japan). The ultrafine FeSiAl powder, with a nominal composition of Fe_74.3Si_15.9Al_9.8, was supplied by Hunan Hualiu New Material Co., Ltd (Changsha, China). The FeSiAl powder was blended with nanocrystalline FeSiBCuNb powder in varying weight proportions, denoted as 100-y:y, where y represents the FeSiAl content ranging from 0 to 80 wt.%. A silicone resin binder, comprising 3 wt.% of the total mix, was dispersed in ethanol after vigorous stirring for 10 min. The blended powders were subsequently incorporated into this solution and stirred until all the ethanol evaporated. The prepared samples were dried in a vacuum oven at 60 °C for one hour. Toroidal-shaped composites, featuring an outer diameter of 10.2 mm and an inner diameter of 5.1 mm, were produced via cold pressing under uniaxial compression at 1800 MPa and room temperature. The powder cores underwent a carefully controlled annealing process in an argon atmosphere at 450 °C for 8 h. This annealing step is essential for alleviating internal stresses and significantly enhancing mechanical strength, thereby ensuring the high quality of the final materials.

2.2. Experimental Materials

The particle size and distribution (PSD) of the raw FeSiBCuNb and FeSiAl powders were examined using a laser particle size analyzer (Bettersize 2000, Bettersize Instruments Ltd., Dandong, China). The microstructural features of both the powders and NSMCs were investigated using field-emission scanning electron microscopy (SEM, JSM-6490LV, JEOL Ltd., Tokyo, Japan). The structural properties of the powders were evaluated using X-ray diffraction (XRD) with a Rigaku D/max-2200PC instrument, utilizing Cu Kα radiation across a 2θ range of 20° to 90°. The density of the NSMCs was determined using the Archimedes displacement method. The magnetic hysteresis behavior of the NSMCs was assessed using a vibrating sample magnetometer (VSM, Lakeshore 7404-s, Lake Shore Cryotronics, Ltd., Westerville, OH, USA). Core loss measurements for the NSMCs were performed using a B–H analyzer (SY-8218, IWATSU ELECTRIC Co., Ltd., Tokyo, Japan). Additionally, the inductance and DC-bias performance of the NSMCs were evaluated using a high-precision LCR meter (Agilent 4285A, Agilent Technologies Inc., Santa Clara, CA, USA) coupled with a DC-bias power supply.

The µ_e of the NSMCs was calculated from the inductance using the following Equation (1) [21]:

$${\mu }_{\mathrm{e}}={\displaystyle \frac{L{l}_{\mathrm{e}}}{{\mu }_0{N}^2{A}_e}}$$

(1)

where, L represents the measured inductance, l_e is the effective magnetic circuit length of the NSMCs, ${\mu }_0$ is the permeability of the vacuum, N is the number of turns of insulated copper wire coiled around the core, and $A_e$ is the effective cross-section area of the NSMCs.

3. Results and Discussion

3.1. Characteristics of Raw Powders

Figure 1a,b show the PSD of the FeSiBCuNb and FeSiAl powders, respectively. The d₅₀ of FeSiBCuNb powder is 25 μm, whereas that of FeSiAl powder is 2.79 μm, and the parameter d₅₀ indicates that half of the particles in each sample are of a smaller size than the specified measurement. The density of the NSMCs was notably affected by the relative sizes of the primary and secondary particles. This factor plays a crucial role in determining µ_e [22]. Here, the FeSiBCuNb powder was significantly larger than the ultrafine FeSiAl powder, allowing the latter to fill the spaces between the FeSiBCuNb particles rapidly. In addition, the ultrafine FeSiAl powder exhibits remarkable plasticity, which can improve the density and uniformity of NSMCs during the subsequent pressing process. Figure 1a,b show the SEM microstructures of the FeSiBCuNb and FeSiAl powders, respectively. The FeSiBCuNb powder produced through gas–water atomization displays irregular shapes. In contrast, the FeSiAl particles were nearly spherical and significantly smaller than those of the FeSiBCuNb powder. The reduced particle size of FeSiAl leads to an increased total surface area, which promotes spontaneous aggregation of the particles.

Figure 1c presents the XRD pattern of the FeSiBCuNb powder, revealing a biphasic structure consisting of an amorphous matrix embedded with nanocrystalline grains. The diffraction pattern exhibits three distinct crystalline peaks at 2θ = 45°, 65°, and 83°, corresponding to the (110), (200), and (211) crystallographic planes of the α-Fe(Si) phase, confirming the partial devitrification of the amorphous precursor during annealing [17]. The formation of the α-Fe(Si) nanocrystalline phase arises from a primary crystallization process, where Cu and Nb act as nucleation-enhancing elements by inducing compositional fluctuations that lower the activation energy for crystallization. Concurrently, the residual amorphous phase contributes to magnetic softening by suppressing intergranular exchange coupling and mitigating magnetocrystalline anisotropy.

In contrast, Figure 1d displays the XRD pattern of the FeSiAl powder, where the three prominent peaks at 2θ = 45°, 65°, and 83° are indexed to the (200), (400), and (422) planes of an Fe_0.3Si₃Al_0.7 crystal phase, indicative of a face-centered cubic structure (FCC) [23]. This phase originates from the high-temperature solid-state reaction between Fe, Si, and Al during gas atomization, where the rapid solidification kinetics suppress equilibrium phase separation, leading to a metastable solid solution [24]. The larger grain size (about 26 nm) compared to FeSiBCuNb (about 10 nm, calculated using Scherrer’s formula [18]) was attributed to the absence of grain-growth inhibitors and the higher diffusivity of Al in the Fe–Si lattice, which accelerates coarsening during powder synthesis. The disparity in grain sizes directly influences the magnetic properties, as finer grains in FeSiBCuNb enhance resistivity and reduce eddy current losses, whereas the more ordered FCC phase in FeSiAl favors higher saturation magnetization, but with increased hysteresis losses.

3.2. Microstructure of NSMCs

To observe the distribution of FeSiAl in the NSMCs and the filling effect between the particles, Figure 2a–f show the morphology of the NSMCs with different FeSiAl contents. Figure 2a,b show that when the FeSiAl content was 0 and 20 wt.%, the interfilling effect between the powders was incomplete. Many gaps still exist between the nanocrystalline powders, which is the reason for the low density and permeability of NSMCs. At an FeSiAl content of 40 wt.%, many deformed FeSiAl particles (marked by yellow circles) appeared in the NSMCs, as illustrated in Figure 2c, causing a notable decrease in the air gap quantity and leading to a denser and more compact structure. However, it should be noted that as the content of FeSiAl continues to increase, the small-sized FeSiAl replaces the nanocrystalline powders, as illustrated in Figure 2e,f. Although FeSiAl can still fill the gaps between the nanocrystalline powders, it agglomerates and introduces numerous small interfaces and gaps, which may adversely affect the structure and magnetic characteristics of NSMCs.

EDS analysis assessed the elemental distribution in the cores containing 50 wt.% FeSiAl to examine the infiltration of ultrafine FeSiAl particles into the interstitial spaces of nanocrystalline powders. The results depicted in Figure 3 highlight characteristic elements, such as Fe, Si, Cu, Nb, and Al. From Figure 3d,e, the highlighted regions represent the presence of the FeSiBCuNb powder, including Cu and Nb. In Figure 3f, the highlighted area shows a high concentration of Al within the FeSiAl powders. Figure 3b,c for Fe and Si illustrate that these elements, common to FeSiBCuNb and FeSiAl, are distributed uniformly. These findings demonstrate that incorporating ultrafine FeSiAl particles into FeSiBCuNb powders effectively fills the gaps between nanocrystalline particles, significantly enhancing the structural integrity of the composite cores.

3.3. Saturation Magnetization and Coercivity of NSMCs

The saturation magnetization of the materials directly influences the DC bias of NSMCs, whereas the coercivity directly influences hysteresis loss [25]. Figure 4a shows the hysteresis loops of NSMCs with different FeSiAl contents, and the derived saturation magnetization and coercivity are shown in Figure 4b. The hysteresis loops of all the samples were narrow, indicating good soft magnetic properties. Although the saturation magnetization of FeSiAl is lower than that of nanocrystalline powders, the saturation magnetization of NSMCs initially increases and then decreases with the addition of FeSiAl powders. This phenomenon can be explained by the fact that when the FeSiAl content increased from 0 to 50 wt.%, a small amount of FeSiAl filled the voids and increased the density, enhancing the overall magnetic properties. As the proportion of FeSiAl exceeded 50 wt.%, its lower saturation magnetization became dominant, whereas the rise in non-magnetic phases and weakened magnetic domain coupling led to a reduction. This phenomenon reflects synergistic and competitive interactions between the two materials. The resistance trend is opposite to that of the saturation magnetization, and the lowest coercivity was 4.36 Oe when the FeSiAl ratio was 50 wt.%. Usually, the coercivity of magnetic materials is closely related to their defects [26]. During magnetization, the domain walls move and flip in the direction of magnetization. At the same time, defects pin the domain walls, making it difficult for them to rotate, thus increasing the coercivity. As shown in Figure 2a–d, when the FeSiAl content ranges from 0 to 50 wt.%, incorporating FeSiAl effectively fills the large voids between the nanocrystalline powders. This leads to a significant reduction in structural defects and a corresponding decrease in the interparticle demagnetization field, which reduces the coercivity. However, the excessive addition of FeSiAl introduces many small gaps between the FeSiAl particles, which increases the demagnetization field and coercivity. Another possible reason for the increase in coercivity is that FeSiAl has a higher coercivity than the FeSiBCuNb powder [27].

3.4. Effective Permeability of NSMCs

Figure 5a illustrates the variation in μ_e of NSMCs containing varying proportions of FeSiAl across a frequency range from 100 kHz to 1000 kHz, and Figure 5b presents the density and resistance of NSMCs containing different amounts of FeSiAl. The density was calculated by dividing the weight of NSMCs by their volume. The μ_e values of all the samples remained consistent within the 1 MHz frequency range, suggesting that these NSMCs are well-suited for high-frequency applications. It can be seen that as the FeSiAl content increased from 0 to 50 wt.%, the μ_e exhibited a rapid rise. The highest value of 48.7 occurred at 50 wt.% FeSiAl content, showing a highly consistent trend with the density; the highest value of density was 6.22 g/cm³ at 50 wt.% FeSiAl. After 50 wt.%, the μ_e and the density decreased gradually, mainly due to the destruction of the continuous magnetic path of the nanocrystals, resulting in the reduction of magnetization efficiency. In addition, the random distribution of FeSiAl particles enhances the demagnetizing effect, whereas the oxidation layer and stress concentration area at the interface of the two phases hinders the magnetic domain transmission, further inhibiting the density and μ_e performance, and excess FeSiAl may introduce more air gaps, which worsens the effective permeability. Equation (2) [12] illustrates the relationship between the density and permeability.

$${\mu }_{\mathrm{e}}={\displaystyle \frac{{\rho }^{\prime }+\frac{2m\prime }{v}}{{\rho }^{\prime }-\frac{m\prime }{v}}}$$

(2)

In this equation, ρ′ is the density of NSMCs, m′ is the weight of the NSMCs, and v is the volume of NSMCs. When the material remains constant, the permeability directly correlates with density. Hence, μ_e improvement is predominantly driven by the elevated density achieved under higher compaction pressures. Furthermore, the resistive behavior exhibits an inverse correlation with both μ_e and material density. Therefore, as the FeSiAl content increases from 0 to 50 wt.%, the enhancement of µ_e is mainly attributed to the increase in density.

The density and resistance data are consistent with the NSMC morphology observed using SEM, as illustrated in Figure 2a–f. When the FeSiAl content ranged from 0 to 50 wt.%, the gaps between the nanocrystalline powders can be effectively filled with small-sized FeSiAl, increasing the density. The increased density makes electron conduction more efficient by improving particle contact, reducing pores, weakening grain boundary effects, and optimizing conductive channels, ultimately leading to lower resistance [17]. However, when the ratio of FeSiAl exceeded 50 wt.%, the agglomerated FeSiAl introduced numerous small gaps in the NSMCs, reducing the density and increasing the resistance.

3.5. Core Loss of NSMCs

The core loss of electronic devices significantly influences their energy conversion efficiency and operational lifespan. It is essential to reduce core loss to improve the high-frequency performance of electronic components. Figure 6a illustrates P_cv at 50 mT for NSMCs with varying FeSiAl content as a function of frequency. P_cv increases rapidly as the magnetic field frequency increases. At the same frequency, the P_cv initially decreases as the FeSiAl content increases from 0 to 50 wt.%, and then rises, reaching its lowest value of 119.35 kW/cm³ at 50 wt.% under 100 kHz. Loss separation analysis was performed to gain insight into the underlying physical mechanisms driving the observed loss variations. Drawing from previously established models, P_cv comprises three main components: hysteresis loss (P_hv), eddy current loss (P_ev), and residual loss (P_rv). Equation (3) describes these components [28].

$$P_{\mathrm{c}\mathrm{v}}=P_{\mathrm{h}\mathrm{v}}+P_{\mathrm{e}\mathrm{v}}+P_{\mathrm{r}\mathrm{v}}$$

(3)

P_hv, P_ev, and P_rv are expressed by Equations (4)–(6) [27,29], respectively.

$$P_{\mathrm{h}\mathrm{v}}=f\oint HdB=k_{\mathrm{h}\mathrm{v}}{B}^{3}f$$

(4)

$$P_{\mathrm{e}\mathrm{v}}={\displaystyle \frac{k_{\mathrm{e}\mathrm{v}}{B}^2{d_{eff}}^2}{\rho }}{f}^2$$

(5)

$$P_{\mathrm{r}\mathrm{v}}=k_{\mathrm{r}\mathrm{v}}{B}^{1.5}{f}^{1.5}$$

(6)

In these equations, f denotes the magnetic field frequency, H represents the applied magnetic field, d corresponds to the effective powder diameter, B signifies the magnetic flux density, ρ is the resistivity, and k_hv, k_ev, and k_rv are the coefficients for hysteresis, eddy current, and residual losses, respectively. The hysteresis loss component (P_hv) scales linearly with frequency, whereas the eddy current loss (P_ev) exhibits a quadratic dependence on frequency, and the residual loss (P_rv) follows the 1.5th power of the frequency.

Figure 6b displays the P_cv/f profiles for NSMCs with varying FeSiAl contents. The nearly linear relationship between P_cv/f and f implies that the residual loss (P_rv) is negligible under these conditions. Consequently, the total core loss (P_cv) can be simplified to Equation (7).

$$P_{\mathrm{c}\mathrm{v}}=P_{\mathrm{h}\mathrm{v}}+P_{\mathrm{e}\mathrm{v}}$$

(7)

According to Equation (4), P_hv corresponds to the energy loss per unit volume per magnetization cycle. This parameter scales directly with the area enclosed by the hysteresis loops and is predominantly governed by coercivity. From Figure 3b, it can be seen that the coercivity of the NSMCs decreased as the FeSiAl content increased from 0 to 50 wt.%, and then increased after 50 wt.%, which is in strong agreement with the trend of P_hv variation with FeSiAl content, suggesting a loss of origin, as shown in Figure 6c. The generation of P_ev in ferromagnetic materials magnetized in an alternating current magnetic field is a consequence of Faraday’s law [30]. From Equation (5), it can be observed that P_ev is proportional to the square of the effective diameter of the particles and inversely proportional to the resistivity of the NSMCs. The effective diameter of the particles in the NSMCs decreases with the addition of ultrafine FeSiAl, owing to the filling effect of ultrafine FeSiAl and the much smaller resistivity of FeSiAl compared to FeSiBCuNb powder [31,32]. P_ev decreases when the content of FeSiAl gradually increases, as shown in Figure 6d.

3.6. DC-Bias Performance

Inductors primarily operate under AC conditions; however, the influence of the DC stray fields cannot be ignored. These DC fields create a bias magnetic field that may push magnetic composites toward magnetic saturation, resulting in decreased permeability and possible inductor malfunction. Consequently, it is essential to ensure superior DC-bias performance in NSMCs. Figure 7a shows the variation in permeability of NSMCs with varying FeSiAl content at 100 kHz, showing a decline in percent permeability with increasing DC magnetizing field. Figure 7b highlights the relationship between DC-bias performance and the FeSiAl content at 100 Oe, revealing a decrease in performance from 75.16% to 73.29% as the FeSiAl content increased from 0 to 50 wt.%, followed by an improvement to 74.57% at 80 wt.% FeSiAl. The variation trend in other fields is consistent with that of 100 Oe. This behavior can be attributed to the magnetization process: materials with lower saturation magnetization and higher permeability are more susceptible to magnetic saturation in the presence of DC-bias fields [33]. Without FeSiAl, FeSiBCuNb exhibits a large air gap, creating a strong demagnetization field and low permeability, making saturation more difficult and enhancing DC-bias performance. As the FeSiAl content increased from 0 to 50 wt.%, the saturation magnetization increased linearly, but rapid permeability growth degraded the DC-bias performance. Above 50 wt.%, reduced permeability improved DC-bias performance. As the FeSiAl content increased from 50 wt%, the decline in saturation magnetization and permeability contributed to the enhanced DC-bias performance of the NSMCs. In addition, as the FeSiAl content increases, the high saturation magnetic induction strength of FeSiAl becomes dominant, enhancing the anti-saturation ability of the NSMCs.

Table 1. A comparative analysis of the electromagnetic properties of the NSMCs investigated in this study and those reported in previous literature.

Samples	μe 100 kHz	Pcv (kW/m3)		DC Bias (%)100Oe	References
		50 mT/ 100 kHz	20 mT/ 1000 kHz
FeSiBCuNb	31	183.4	765.3	75.2	This work
FeSiBCuNb/50 wt.% FeSiAl	48.7	119.4	416.6	73.3	This work
FeSiBPCNbCu	51.5	107	/	52	[25]
FeSiBCuNb	49.1	135.6	/	60.3	[34]
FeSiBCuNb	33.32	/	/	85	[35]
FeSiBCuNb	29.38	/	786	67.28	[36]
FeSiBCuNb/CIP	74.8	/	607	/	[37]
FeSiBCuNb/CIP	35.3	281.8	915.2	/	[17]
FeSiBCuNb/CIP	/	/	748.4	>94	[27]
FeSiBC/CIP	38.6	/	691	85	[38]
FeSiBC/CIP	31	/	762.66	81.76	[39]
FeSiBC/15% FeNi	45.82	/	/	/	[14]

shows the comparison of electromagnetic characteristics between the NSMCs examined in this study and Fe-based powder cores from previous research highlights the impact of modifying the FeSiAl content. By adjusting the FeSiAl content, the researchers were able to develop NSMCs with significantly higher μ_e and lower P_cv. This improvement is significant for producing compact and highly efficient power electronic devices, especially those designed for high-frequency operation. Higher μ_e allows for better magnetic performance, whereas lower P_cv reduces energy dissipation, leading to more efficient devices. These advancements align with the increasing demand for miniaturized and energy-efficient power electronics in modern applications.

4. Conclusions

This study systematically examined the impact of varying the ultrafine FeSiAl mass ratio on the soft magnetic properties of FeSiBCuNb/FeSiAl NSMCs. Additionally, the mechanism by which the addition of FeSiAl influences the magnetic properties was investigated. The results demonstrate that increasing the ultrafine FeSiAl content from 0 to 50 wt.% allowed the gaps between nanocrystalline powders to be effectively filled. This significantly increased the density of the NSMCs. Consequently, the hysteresis loss, coercivity, and core loss decreased, and μ_e increased. When the FeSiAl content exceeded 50 wt.%, the agglomerated FeSiAl introduced numerous small gaps in the NSMCs, which adversely affected performance. Thus, the NSMCs prepared with the addition of 50 wt.% FeSiAl exhibit excellent magnetic properties, with a high μ_e of 48.7, a low P_cv of 119.35 kW/cm³ at 100 kHz under 50 mT, and a high DC-bias performance of 73.29% at 100 Oe. These findings provide both a fundamental understanding of phase-mixing effects in soft magnetic composites and a practical solution for high-frequency power electronics, particularly for molded inductors requiring compatibility with delicate copper windings. The developed material system offers significant potential for advancing energy-efficient power conversion technologies while providing a generalizable approach for designing composite soft magnetic materials through controlled phase engineering.