Impact of Compaction Pressure and Heat Treatment Temperature on the Performance of FeSiBCuNb/FeNi Soft Magnetic Composites

Abstract

FeSiBCuNb powders, produced via the gas–water atomization method, typically exhibit a broad particle size distribution and high sphericity. Nanocrystalline soft magnetic composites derived from these powders demonstrate exceptional service stability. In this study, a series of FeSiBCuNb/FeNi nanocrystalline magnetic powder cores (NMPCs) were fabricated under varying compaction pressures and heat treatment temperatures. The effects of these parameters on the soft magnetic properties were systematically analyzed. The findings reveal that optimizing compaction pressure and heat treatment temperature significantly enhances the density of the composite powders, leading to improved magnetic permeability and reduced core loss; when compaction pressure is 1800 MPa and heat treatment temperature is 550 °C, the NMPCs display outstanding magnetic properties with a low H_c of 6.32 Oe, high μ_e of 71.9, a low P_cv of 86.3 kW/m³ at 50 mT and 100 kHz, and 351.5 kW/m³ at 20 mT and 1000 kHz. Therefore, tailoring these processing conditions can enhance the soft magnetic performance of FeSiBCuNb nanocrystalline composites.

1. Introduction

Magnetic powder cores (MPCs) play a crucial role in modern electronics and power industries, serving as essential functional materials in inductors, transformers, and electromagnetic devices [1,2]. Optimizing their performance is vital for enhancing the efficiency, stability, and reliability of electronic systems [3,4]. In recent years, the adoption of wide-bandgap semiconductor materials has significantly advanced power conversion devices and motor control systems, enabling their operation at considerably higher frequencies [5,6].

Among MPCs, NMPCs have garnered increasing attention due to their unique composition and exceptional performance potential [7]. Over the last few decades, extensive studies have focused on amorphous materials and, more recently, nanocrystalline materials for application in magnetic devices that necessitate magnetically soft components, such as transformers and inductive components [8,9]. Recently, there has been a notable surge in interest surrounding nanocrystalline soft magnetic alloys [10]. This growing attention can be attributed to the fact that these alloys possess traits typically found in both amorphous and crystalline materials, enabling them to effectively rival conventional alternatives within these categories [11,12]. The benefits of nanocrystalline alloys stem from their nanoscale chemical and structural heterogeneities, including high effective magnetic permeability (μ_e), low coercivity (H_c), low core loss (P_cv), and near-zero magnetic anisotropy [13,14], which are instrumental in achieving superior magnetic characteristics. However, the final properties of NMPCs are significantly influenced by processing conditions, particularly compaction pressure and heat treatment temperature, making this a focal point of research [15,16].

Compaction pressure is a critical parameter in NMPC fabrication, as it directly affects inter-particle contact, microstructural characteristics, and overall material density [17]. Appropriate compaction pressure enhances particle contact, thereby increasing permeability and magnetic saturation induction [18,19]. However, excessive compaction pressure can distort the magnetic domain structure, leading to degraded magnetic properties [20,21]. One of the key challenges in magnetic material engineering is improving NMPC compaction density without excessively increasing the applied pressure [22].

Similarly, heat treatment temperature is a fundamental factor in NMPC optimization [23]. Heat treatment induces various physical and chemical transformations, such as grain growth, phase transitions, and stress relaxation [24,25]. These changes significantly impact the magnetic, mechanical, and thermal stability of NMPCs [26]. Therefore, selecting an appropriate heat treatment temperature is essential for achieving optimal performance [27,28].

In our previous study [29], we developed FeSiBCuNb/FeNi NMPCs by incorporating 50 wt.% FeNi powder into FeSiBCuNb nanocrystalline powder and compacting the mixture into cores. This approach resulted in significant improvements, including an effective permeability (μ_e) of 59.3, a DC-bias performance of 65.6% at 100 Oe, and a core loss (P_cv) of 99.8 kW/m³ at 100 kHz under 50 mT. These enhancements were attributed to FeNi particles filling interstitial voids, thereby improving the soft magnetic performance of NMPCs.

Several studies have investigated the effects of compaction pressure and heat treatment on NMPC properties. For instance, Zhang et al. [30] analyzed the influence of the carbonyl iron powder (CIP) mass ratio and compaction pressure on Fe-based amorphous soft magnetic composites, reporting that increased compaction pressure enhances μ_e while having minimal impact on P_cv. Li et al. [31] studied the effects of annealing duration on FeBPCCu nanocrystalline alloys and found that prolonged annealing facilitates residual stress relaxation but also leads to excessive grain growth, increasing H_c while reducing μ_e. Furthermore, Li et al. [15] demonstrated that higher gas-atomization pressure results in greater amorphous content and smaller crystallite size in FeSiBCuNb powders, improving soft magnetic performance, particularly after annealing at 550 °C for 60 min. Tian et al. [16] systematically evaluated the effects of heat treatment and compaction pressure on FeSiBNbCu/SiO₂ soft magnetic composites, showing that optimal annealing conditions produced an NMPC with a μ_e of 84 and P_cv of 174 kW/m³ at 50 kHz under 0.1 T. Pan et al. [19] also optimized compaction and annealing processes to enhance the soft magnetic properties of iron-based composites.

Despite extensive research on the influence of compaction pressure and heat treatment temperature on NMPC properties, existing studies often report varying optimal parameters due to differences in material composition and processing methods. A comprehensive and systematic investigation to establish optimal processing conditions is still lacking. Therefore, this study aims to systematically examine the effects of compaction pressure and heat treatment temperature on the soft magnetic properties of FeSiBCuNb/FeNi NMPCs. Through systematic identification of optimal processing parameters, this research establishes a performance-driven optimization framework for NMPC controllers, demonstrating measurable efficiency improvements that support practical implementation in high-frequency power conversion devices and data transmission networks.

2. Experimental Details

2.1. Preparation of FeSiBCuNb/FeNi NMPCs

In this research, commercial atomized FeSiBCuNb nanocrystalline powder (D₅₀ = 25 μm) was sourced from Epson Atmix Corporation (Hirosaki, Japan), with a composition of 13.5 at.% Si, 9 at.% B, 1 at.% Cu, 3 at.% Nb, and a balance of Fe. The FeNi powder (D₅₀ = 3 μm) was provided by Hunan Hualiu New Material Co., Ltd. (Changsha, China), with a composition of 50 at.% Ni and 50 at.% Fe. Two groups of powder cores were prepared to investigate the influences of compaction pressure and heat treatment temperature on the soft magnetic properties of NMPCs.

Firstly, the FeSiBCuNb nanocrystalline powder was mixed with 50 wt.% FeNi powder. Subsequently, 3 wt.% of silicon resin adhesive (99.9%; Penghui Magnetic Material Co., Ltd., Dongguan, China) was mixed into ethanol (99%; Jiangyin Jianghua Microelectronic Materials Co., Ltd., Jiangyin, China) and vigorously stirred for 10 min to ensure complete dissolution of the resin. The mixed powders were introduced into the solution and agitated until complete evaporation of the ethanol. The resultant mixtures were subsequently dried in a vacuum oven at 60 °C for one hour.

Secondly, the samples were divided into 2 groups: in group 1, toroidal FeSiBCuNb/FeNi NMPCs with an outer diameter of 10.2 mm and an inner diameter of 5.1 mm were produced via cold pressing under uniaxial pressures between 800 MPa and 1800 MPa at room temperature. Subsequently, the NMPCs were annealed at 450 °C for 8 h in an argon atmosphere to relieve internal stresses and improve the mechanical strength of the magnetic powder cores. In group 2, the toroidal FeSiBCuNb/FeNi NMPCs with identical dimensions were produced by cold pressing under a uniaxial pressure of 1800 MPa at room temperature and then annealed at temperatures ranging from 450 °C to 550 °C in an argon atmosphere, with all other conditions matching those of group 1.

2.2. Experimental Materials

A scanning electron microscope (SEM, JSM-6490LV, JEOL Ltd., Tokyo, Japan) was used to meticulously examine the surface morphologies of the FeSiBCuNb nanocrystalline powder and FeNi powder. An X-ray diffractometer (XRD, Rigaku D/max-2200PC, Rigaku Corporation, Tokyo, Japan) was used to characterize the structural properties of these powders. In addition, a laser particle size analyzer (Bettersize 2000, Bettersize Instruments Ltd., Dandong, China) was used to examine the raw powders’ particle size and distribution (PSD). A vibrating sample magnetometer (VSM, Lakeshore 7404-s, Lake Shore Cryotronics, Ltd., Westerville, OH, USA) was used to measure the magnetic characteristics of the NMPCs, the Archimedes displacement method was used to determine the density of the NMPCs, and an AC/DC/IR Hipot Tester (model 19073, Chroma ATE Inc., Taoyuan, China) analyzed the resistance of the NMPCs. Furthermore, a B-H curve analyzer (SY-8218, IWATSU ELECTRIC CO., Ltd., Tokyo, Japan) was used to analyze the AC magnetic properties of the NMPCs, and an Agilent 4285A LCR tester (Agilent 4285A, Agilent Technologies Inc., Santa Clara, CA, USA) was used to measure the effective permeability μ_e and DC-bias performance of the NMPCs. Error bars in all experimental procedures, figures, and tables were derived from three samples prepared under each condition. These methods provided a detailed understanding of the physical and magnetic characteristics of the materials under study.

The μ_e of the NMPCs was calculated based on the inductance using Equation (1) [32]:

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

(1)

In this equation, L is the measured inductance, l_e denotes the effective magnetic circuit length of the NMPCs, ${\mu }_0$ is the permeability of the vacuum, N is the number of turns of insulated copper wire coiled around the core, and $A_{\mathrm{e}}$ is the effective cross-section area of the NMPCs.

3. Results and Discussion

3.1. Characteristics of Raw Powders

The PSD of the FeSiBCuNb and FeNi powder are depicted in Figure 1a,b. The D₅₀ of the FeSiBCuNb and FeNi powder are 25 μm and 3 μm, respectively, and the parameter D₅₀ indicates that 50% of the particles in the sample are smaller than this value. Significantly, the reduced size of FeNi powders compared to FeSiBCuNb powders facilitates their effective filling of the spaces between larger particles. As shown in Figure 1a,b, the surface characteristics of the FeSiBCuNb and FeNi powders differ significantly. Most FeSiBCuNb particles are spherical with smooth surfaces, with only a few exceptions being pliable. On the other hand, the surfaces of the smaller FeNi particles are comparatively rough. Figure 1c,d displays the XRD patterns of the FeSiBCuNb and FeNi powders. The results show that the nanocrystalline powders are mainly composed of α-Fe(Si), as demonstrated by the clear diffraction peaks at 45.17°, 65.86°, and 83.30°, corresponding to the (110), (200), and (211) planes of α-Fe(Si). Similarly, the FeNi powders exhibit firm diffraction peaks at 43.68°, 50.91°, and 74.80°, which correspond to the (110), (200), and (220) planes of α-Fe(Ni) [33].

Using the Scherrer equation based on the XRD patterns [9], the average grain sizes of α-Fe(Si) in FeSiBCuNb and α-Fe(Ni) in FeNi were determined, as shown in Equation (2):

$$D={\displaystyle \frac{K\lambda }{Bcos\theta }}$$

(2)

In this equation, K is the Scherrer constant, λ is the X-ray wavelength, and with a selected value of 0.154056 nm in this paper, B is the full width at half maximum (FWHM), and θ is the Bragg angle. According to the results, the average particle size of α-Fe(Si) is roughly 13 nm, and that of α-Fe(Ni) is about 28 nm.

3.2. Impact of Compaction Pressure on Soft Magnetic Properties of NMPCs

3.2.1. Coercivity and Saturation Magnetization

Figure 2a shows the hysteresis loops of NMPCs with different compaction pressures, and the corresponding saturation magnetization and coercivity are demonstrated in Figure 2b. VSM measurements were performed over a magnetic field range from −20,000 Oe to 20,000 Oe. The hysteresis loops of all the samples displayed a narrow, S-shaped profile characteristic, suggesting high saturation magnetization (M_s) and low coercivity (H_c) [34]. Such characteristics highlight the outstanding soft magnetic performance of the samples. Since the crystal structure of NMPCs becomes denser and the atomic spacing decreases with increasing pressure, this effect strengthens the exchange coupling between atoms, resulting in a modest increase in saturation magnetization. As shown in Figure 2b, the saturation magnetization showed an upward trend as the compaction pressure increased. The change was not apparent before 1300 MPa and showed a clear upward trend after 1300 MPa. This is mainly because as the compaction pressure increases, the contact between the grains becomes tighter, the non-magnetic interface is reduced, the magnetic domain structure is optimized, and more magnetic moments are neatly arranged under the external magnetic field.

Furthermore, as depicted in Figure 2b, the coercivity decreases until a compaction pressure of 1300 MPa and then increases with higher compaction pressures. The lowest coercivity value, 5.24 Oe, is recorded at a compaction pressure of 1300 MPa. Coercivity in magnetic materials is typically linked to defects [35]. During magnetization, the movement and reorientation of magnetic domain walls are oriented in the direction of the applied magnetic field. However, defects will constrain the magnetic domain walls, making it difficult to rotate, thus increasing coercivity. At lower compaction pressures, grain boundaries and defects hinder the movement of magnetic domain walls, which causes an increase in coercivity. Nevertheless, when the pressure reaches about 1300 MPa, the coercivity may be the lowest due to the redistribution of stress and the temporary stability of the magnetic domain structure. Subsequently, as the compaction pressure increases, new pinning points are formed, or the grain boundary effect is intensified, and the coercivity rises again. These phenomena result from the interaction between grains, the variation in magnetic domain structure, and the stress effect [36].

3.2.2. Effective Permeability

Figure 3a shows the variation in μ_e, density, and resistance of the NMPCs with respect to frequency under different compaction pressures, ranging from 100 to 1000 kHz. Across this frequency band, the μ_e values of all samples remained stable at 1000 kHz, indicating their suitability for high-frequency applications. Increasing compaction pressure leads to an increase in μ_e, as higher pressure causes the powder particles to become more densely packed, reducing porosity and increasing density. This densification results in a smoother magnetic path, stronger magnetic domain interactions, and a corresponding increase in magnetic permeability. Figure 3b displays the variations in the density and resistance of NMPCs under different compaction pressures. The density increases as the compaction pressure rises, while the resistance trend is opposite. The significant rise in the density can be attributed to enhanced particle rearrangement and tighter packing within the NMPCs. When pressure is applied, the soft magnetic particles are forced into closer proximity, thereby reducing inter-particle voids and leading to a more compact structure, which results in increased density [37]. Meanwhile, the trend in density is consistent with μ_e.

Equation (3) [38] illustrates the relationship between density and permeability:

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

(3)

In this equation, ρ′ is the density of NMPCs, m′ is the weight of the NMPCs, and v is the volume of NMPCs. When the material remains constant, the permeability directly correlates with density. Therefore, as the compaction pressure increases, the enhancement of μ_e is mainly attributed to the increase in density.

Conversely, the observed decrease in resistance with increasing compaction pressure is associated with improved electrical conductivity. In a more densely packed structure, the distance between conductive particles decreases, allowing electrons to travel more easily through shorter conductive paths between adjacent particles. This reduction in path length, combined with the increased contact area between particles under higher compaction pressure, significantly enhances electrical conductivity and reduces overall resistance.

3.2.3. DC-Bias Performance

Inductors typically operate under alternating current. However, a certain amount of direct current dispersion is inevitable within alternating current. Applying a DC-bias field can give rise to magnetic saturation of the composite materials, thereby reducing permeability, inductor malfunction, and potential accidents. Therefore, ensuring that the NMPCs have excellent DC-bias performance is vital. Figure 4a shows that the percentage variation in permeability for NMPCs under various compaction pressures is depicted at 100 kHz. The percentage permeability decreases with the increase in the DC magnetizing field and compaction pressure for all the samples. Figure 4b illustrates the percentage permeability of NMPCs subjected to various compaction pressures in a DC magnetizing field of 100 Oe to better clarify the relationship between DC-bias performance and compaction pressures. It is noted that when the compaction pressure rises from 800 MPa to 1800 MPa, the DC-bias performance of NMPCs decreases from 68.57% to 62.48%. The observed change can be primarily linked to the magnetization properties. Materials exhibiting lower saturation magnetization and higher permeability generally reach saturation more readily in a DC-bias magnetic field [39].

3.2.4. Core Loss

The core loss plays a crucial role in determining the energy conversion efficiency and the lifespan of electronic devices. Consequently, reducing core loss is vital for improving the high-frequency performance of electronic components. Figure 5a depicts the core loss P_cv at 50 mT across different compaction pressures, plotted against frequency for NMPCs. The P_cv of NMPCs rises substantially as the magnetic field frequency increases. At the same frequency, the performance was slightly different under different frequencies. Taking 100 kHz as an example, with the rise in compaction pressure, P_cv exhibits an initial downward trend followed by a subsequent upward, and the lowest value is 91.69 kW/cm³ when the compaction pressure is 1600 MPa. The trend is the opposite at 1000 kHz to that at 100 kHz.

A loss separation study investigated the underlying physical mechanisms driving the observed loss changes. Following the loss separation framework outlined in earlier studies, the P_cv is composed of hysteresis loss (P_hv), eddy current loss (P_ev), and residual loss (P_rv), as described by Equation (4) [40]:

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

(4)

P_rv, which commonly stems from magnetic aftereffects or frequency dispersion, usually has a considerably smaller magnitude than P_hv and P_ev in power applications [41]. It is widely recognized that residual losses only become significant at high-frequency ranges, such as above several megahertz. Moreover, nanocrystalline magnetic powder cores and FeNi powder cores exhibit low magnetostriction, resulting in minimal residual loss. Figure 5b displays the P_cv/f profiles for NMPCs with varying compaction pressures. The nearly linear relationship between P_cv/f and f also implies that the P_rv is negligible under these conditions. Consequently, similar studies [28,35] generally omit residual losses. For practical purposes in the power sector, P_rv was neglected in this study. P_ev predominates at high frequencies and is described by Equation (5) [42]:

$$P_{\mathrm{e}\mathrm{v}}={\displaystyle \frac{C{B}^2{d}^2{f}^2}{\rho }}$$

(5)

In this equation, C is the proportionality factor, B is the magnetic flux density, d is the material thickness, f is frequency, and ρ is resistivity. The value of P_ev rises with the square of the frequency and falls with higher resistivity. This distinct mathematical relationship is reliable for assessing material behavior at different frequencies.

Figure 5c,d clearly shows the P_hv and P_ev values. The findings indicate a clear pattern: the P_hv value decreases when compaction pressure rises from 800 MPa to 1300 MPa, followed by an increase as the compaction pressure continues to rise from 1300 MPa to 1800 MPa, while the trend of P_ev is opposite to that of P_hv. This trend, mirroring the variations in coercivity, highlights a direct link between hysteresis loss and coercivity. The connection is rooted in the fact that hysteresis loss is determined by the energy expended in moving magnetic domain walls and rotating domains during magnetization. Coercivity, representing a material’s resistance to alterations in magnetization, is influenced by its microstructure and magnetic attributes. P_ev is related to the powders’ adequate particle size and the NMPCs’ resistivity. The particle size of the powders remains unaffected by variations in compaction pressure. Under the condition of 800 MPa to 1300 MPa, as compaction pressure rises, the space between powder particles reduces, decreasing the porosity and lowering the resistivity of the magnetic core, so the eddy current loss increases. When the pressure exceeds 1300 MPa, the resin’s fluidity improves under high pressure, resulting in a more uniform and denser organic insulating coating on the powder surface, which reduces eddy current losses.

3.3. Impact of Heat Treatment Temperatures on Soft Magnetic Properties of NMPCs

3.3.1. Coercivity and Saturation Magnetization

Figure 6a illustrates the hysteresis loops of NMPCs subjected to varying heat treatment temperatures within a magnetic field ranging from −20,000 Oe to 20,000 Oe. The hysteresis loops for all samples exhibit a narrow, S-shaped profile, which signifies their excellent soft magnetic characteristics. Figure 6b presents the variation in saturation magnetization and coercivity of NMPCs across different heat treatment temperatures. As the temperature increased, the saturation magnetization and coercivity gradually declined, with the lowest values observed at 550 °C. That is because the increase in heat treatment temperature causes a decrease in internal stress, which leads to a reduction in coercivity.

3.3.2. Effective Permeability

Figure 7a illustrates how the μ_e of NMPCs varies with frequency at different heat treatment temperatures between 100 kHz and 1000 kHz. Across all tested frequencies, the μ_e of the samples remained consistent, and these findings suggest that NMPCs are especially suitable for applications requiring high frequencies. At the same time, we can see that the μ_e of NMPCs increases with the temperature and reaches its highest at 550 °C, with an average of 71.66. The reason may be that as the temperature of the heat treatment rises, the grain boundary of the NMPCs may be reduced, the internal residual stress is released, and the resistance to magnetic domain wall motion is decreased; then, the permeability is increased. It is clear that an increase in heat treatment temperature substantially impacts the enhancement of effective permeability. Figure 7b illustrates the trends in the density and resistance of NMPCs at various heat treatment temperatures. As the temperature increases from 450 °C to 550 °C, the density of NMPCs decreases first and then increases, while the trend for resistance is the opposite. It can be concluded that when the temperature is below 500 °C, due to the slower rate of atomic diffusion, some elements may aggregate in local areas, resulting in uneven local composition, which in turn causes a decrease in local density; at this time, the electron scattering is enhanced, the atomic arrangement at the grain boundary is more disorderly, and the resistance of electrons across the grain boundary is increased, and then the resistance is increased. As the temperature rises, the atom diffusion rate is accelerated, the element diffusion is more uniform, and the composition inside the material tends to be consistent, which helps to eliminate the difference in density caused by the uneven composition so that the overall density tends to stabilize and increase; meanwhile, the increase in temperature promotes the diffusion of atoms, so that the impurities are evenly distributed, the scattering of electrons is reduced, the carrier is released from the trap, and the carrier concentration is increased. These factors work together to reduce the resistance [43].

3.3.3. DC-Bias Performance

Figure 8a illustrates the relationship between the DC-bias performance of NMPCs, subjected to various heat treatment temperatures at 1 V/100 kHz, and the DC magnetic field ranging from 20 Oe to 100 Oe. Figure 8b illustrates the percentage permeability of NMPCs subjected to various heat treatment temperatures in a DC magnetizing field of 100 Oe to better clarify the relationship between DC-bias performance and heat treatment temperatures. It is evident that the DC-bias performance of NMPCs gradually declines as both temperature and magnetic field strength increase. However, even at an applied field of 100 Oe, the performance remains above 56.84%, sufficient to meet the requirements for devices with significant current density. This may be caused by the acceleration of atomic diffusion at high temperatures, the more orderly internal structure of the NMPCs, the reduction in defects, and the further reduction in hysteresis loss. These factors make the NMPCs more easily magnetized under the external magnetic field, gradually reducing DC-bias.

3.3.4. Core Loss

Figure 9 illustrates how the core loss of NMPCs varies with temperature across a frequency range of 100 kHz to 1000 kHz under 50 mT. As the temperature increases, it is evident that the P_cv shows a downward trend, as shown in Figure 9a. Figure 9b displays the P_cv/f profiles for NMPCs with varying heat treatment temperatures. The nearly linear relationship between P_cv/f and f also implies that the P_rv is negligible under these conditions. Figure 9c,d, respectively, shows the separated losses of NMPCs at different temperatures and the extracted P_hv and P_ev. With the temperature increase, the P_hv decreases, and the P_ev shows a downward trend. Higher temperatures are believed to promote a more compact structure with decreased porosity, which diminishes the pinning effect of magnetic domains. Consequently, this leads to a reduction in the P_hv value. Meanwhile, the variation in P_hv is closely related to coercivity [44]. As for the changing trend of P_ev, the variation in which is closely associated with the resistance of NMPCs, the P_ev is inversely proportional to the resistance. The decrease in resistance may lead to an increase in P_ev.

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

Samples	μe 100 kHz	Pcv (kW/m3)		DC Bias (%) 100 Oe	References
		50 mT/ 100 kHz	20 mT/ 1000 kHz
FeSiBCuNb/50 wt.% FeNi (550 °C,1800 Mpa)	71.9	86.3	351.5	56.8	This work
FeSiBPCNbCu	51.5	107	/	52	[13]
FeSiBCuNb	33.32	/	/	85	[15]
FeSiBCuNb	49.1	135.6	/	60.3	[45]
FeSiBCuNb	29.38	/	786	67.28	[46]
FeSiBCuNb/CIP	35.3	281.8	915.2	/	[35]
FeSiBCuNb/CIP	74.8	/	607	/	[36]
FeSiBCuNb/CIP	/	/	748.4	>94	[47]

compares the electromagnetic properties of the FeSiBCuNb/FeNi powder cores investigated in this study with those of Fe-based powder cores studied in previous research. Adjusting the compaction pressure and heat treatment temperatures made it possible to produce FeSiBCuNb/FeNi powder cores with significant permeability and minimal core loss, aligning with the trend towards smaller, more efficient power electronic devices suitable for high-frequency operation.

4. Conclusions

In summary, this study systematically investigated the impacts of compaction pressures and heat treatment temperatures on the magnetic properties of FeSiBCuNb/FeNi composite cores. We examined important high-frequency electromagnetic characteristics, including effective permeability (μ_e), core loss (P_cv), and DC-bias performance. When the heat treatment temperature is 450 °C, as compaction pressures increase, the coercivity initially decreases and then slightly increases, while μ_e showed an apparent rise; meanwhile, DC-bias performance declines, but the trend for P_cv is less distinct; the overall performance is optimal when compaction pressure is 1800 MPa. Under 1800 MPa compaction pressure, when heat treatment temperatures increase from 450 °C to 550 °C, the coercivity and DC-bias of NMPCs decrease, the μ_e rises significantly, and the core loss P_cv shows a downward trend; the best overall performance is achieved at a heat treatment temperature of 550 °C. When the compaction pressure is 1800 MPa and heat treatment temperature is 550 °C, the NMPCs display outstanding magnetic properties with a low H_c of 6.32 Oe, high μ_e of 71.9, a low P_cv of 86.3 kW/m³ at 50 mT and 100 kHz, and 351.5 kW/m³ at 20 mT and 1000 kHz. Therefore, suitable compaction pressure and heat treatment optimization could optimize the soft magnetic properties of FeSiBCuNb nanocrystalline composites.