FeSiAl Soft Magnetic Composites Research Articles

MHz High Performance of Soft Magnetic Composite with Ordered Domain Structure for Efficient Conversion of Electrical Energy

AbstractSoft magnetic materials are a core element of power electronics and electrical machines. However, none of the soft magnetic materials is able to exploit the full potential of wide bandgap semiconductors, which operate above MHz frequency for efficient energy conversion in power electronic systems. Here, a high‐performance Fe–Si soft magnetic composites with a 2D ordered domain structure are reported, enabling efficient energy conversion at MHz frequencies. By transforming spherical particles into flakes and arranging them in layers, 2D magnetic domains are created within the composite. This leads to a 90% increase in permeability and a tenfold decrease in loss at 3 MHz compared to composite made with spherical particles. The significantly increased cut‐off frequency indicates that the ordered flaky particles are suitable for MHz applications, unlike the disordered spherical particles. These findings provide an effective approach for fabricating high performance soft magnetic composites from traditional spherical particles and miniaturizing magnetic devices for efficient power electronics operation.

Significantly improved magnetic properties of FeSiAl soft-magnetic composites by adding FeSi fine particles and regulating annealing temperature

In this work, the effects of adding FeSi fine particles and regulating temperature on the magnetic properties of FeSiAl soft magnetic composites (SMCs) are studied. It shows that the addition of FeSi fine particles can effectively fill the pores among FeSiAl particles, reducing the content of non-magnetic substances and improving the density of the SMCs. Meanwhile, the saturation magnetization and DC-bias characteristics are enhanced. And the optimal particle mixture structure and best magnetic properties of SMCs are achieved when doping with 30 wt% FeSi fine particles. Additionally, increasing the annealing temperature to 700 °C is beneficial to eliminate the residual stress and structural defects, which further optimizes the magnetic properties of the SMCs. However, when the annealing temperature is increased to 800 °C, the insulation layer is severely destroyed, resulting in the deteriorated frequency stability and increased core loss.

Research on loss characteristic of soft magnetic composites under nonsinusoidal excitations with DC bias field

Choosing a suitable core loss model and accurately predicting energy loss are crucial in designing magnetic devices with high efficiency based on soft magnetic composites (SMCs). In this work, FeSiAl and FeSi SMCs with a uniform insulating layer were fabricated by a phosphating process. The effects of excitation waveform and DC bias field on core loss have been investigated in depth. The results show that different remagnetization rates of SMC under ideal sinusoidal and square waves result in different core losses at the same frequency and flux density. The improved general Steinmetz equation and the modified Steinmetz equation were shown to be suitable for calculating core loss under square excitation waves without DC bias field. When the DC bias field is applied, the core loss of FeSiAl and FeSi SMCs was found to increase significantly due to the magnetization state gradually approaching saturation. Interestingly, the variation tendency of core loss can be accurately predicted using the waveform coefficient Steinmetz equation under square excitation conditions with a DC bias environment. This work not only provides deep insights into core loss under different excitation waveforms and DC bias fields but also determines the application scope of different core loss models.

Insulation coating via hydrothermal oxidation for high-frequency FeSiAl soft magnetic composites

Soft magnetic composites (SMCs) play a crucial role in electronic devices owing to their high saturation magnetization. However, conventional insulation methods employed in SMCs exhibit inadequate insulation reliability, thereby restricting their further application in high frequencies. In this study, hydrothermal oxidation is introduced for insulation coating in the preparation of FeSiAl SMCs. When treated at 150 ℃ for 2 h, an insulation layer comprising of Al2O3, SiO2, Fe3O4 and Fe2O3 is formed on the surface of FeSiAl. The most optimal sample is achieved with saturation magnetization of 134.3 emu/g, presenting no significant reduction in saturation magnetization compared to the untreated sample. Cut-off frequency exceeding 300 MHz, and power loss of 503.7 kW/m3 (@7 MHz, 5 mT) are also obtained. This study suggests that hydrothermal oxidation could be a dependable method for fabricating high-frequency SMCs.

Potassium phosphate modulation of the microstructure and its influence on the magnetic properties of FeSiAl soft magnetic composites

FeSiAl soft magnetic composites (SMCs) with phosphate-silicone resin as the insulating layer were prepared by phosphating FeSiAl powder with K3PO4 solution. The effects of K3PO4 content on the microstructure and composition of the insulation coating were investigated. Further, the soft magnetic properties of SMCs were analyzed in detail. It is revealed that the annealed inorganic coating layer which predominantly consists of Al(PO3)3, Al2O3, and P2O5 exhibits a high resistivity, high temperature resistance and thin thickness, significantly reducing the eddy current loss. The outstanding magnetic properties of a power loss of 118.6 kW/m3 (100 kHz, 0.1 T) and permeability of 63.8 were achieved for this high-quality thin insulation coating. Moreover, the magnetic loss was separated into hysteresis, eddy current and excess part, and the mechanism was analyzed in detail. The reduced total loss can be ascribed to the suppression of the eddy current. The novel SMCs coating with K3PO4 are particularly suitable for applications in high frequency and high DC bias situations for switching power supplies, photovoltaic inverter boost inductors and other applications.

Ultralow-loss soft magnetic composites with temperature-resistant and insulated Al2O3/SiO2 layers through pyrolysis

Soft magnetic composites (SMCs) with low power loss are urgently needed to meet the increasing demand for high frequency and miniaturized inductors and transformers. Ultrathin cladding with good insulation and high temperature resistance is the key to achieve low-loss SMCs. In this study, we used MQ silicon resin as precursor to produce in-situ grown Al2O3/SiO2 composite insulating layer in FeSiAl SMCs through pyrolysis process and high-temperature reaction. The morphologies, microstructures and compositions of the coatings on the surface were characterized by SEM, TEM, EDS, TG, XRD, FTIR and XPS, and the results show FeSiAl powders are evenly and entirely covered with an inner Al2O3 and outer SiO2 composite insulating layer. The results of powder resistivity show that the insulating layer still maintains very high resistance after annealing at 750 °C. The composite insulating layer had high resistivity and reduced eddy current loss, while the high temperature annealing process reduced stress and defects and resulted in low hysteresis loss. The best magnetic properties were obtained from samples coated with 2.0 wt% MQ and annealed at 750 °C, with an effective permeability of 76 and the lowest power loss of 72.2 mW/cm3 at 50 mT/100 kHz, 88.5 mW/cm3 at 100 mT/50 kHz and 304.1 mW/cm3 at 100 mT/100 kHz.

Low core loss and high DC bias performance of FeSiAl soft magnetic composites cores with hybrid insulating layers of MgO/SiO2

Soft magnetic composites (SMCs) play an indispensable role in electromagnetic conversion, transmission, and storage. However, in order to achieve miniaturization, energy conservation, and meet the application requirements of premagnetisation in direct-current (DC) components, SMCs are required to have low core loss and high DC bias performance. In this work, FeSiAl SMCs with hybrid insulating layers of MgO/SiO2 have been successfully prepared by the decomposition of magnesium acetate tetrahydrate and silicone resin. The presence of MgO and SiO2 insulating layers can effectively compensate for each other's coating defects, thereby forming complete insulating layers on the surface of FeSiAl powders to reduce the core loss. Finally, the FeSiAl@MgO/SiO2 SMC gets remarkable comprehensive magnetic properties with a low core loss (Pcv) of 163.7 mW/cm3 at 50 mT/100 kHz, a high DC bias performance of 53.7 % at 100 Oe, and an effective permeability (μe) of 46, which is promising for high-frequency and high-power applications.

Structure and magnetic properties of FeSiAl-based composites with the compound passivation agent

FeSiAl soft magnetic composites (SMCs), which are widely used in electromagnetic applications, have good electromagnetic characteristics. To reduce their core loss, the current research focuses on improving the properties of insulating coating materials. In this work, different contents of phosphoric acid and chromic acid compound passivating agents are used to prepare the insulation coating of FeSiAl powder. The results revealed that the surface film layer of the powder coating with the compound passivation agent is relatively smooth, and the film layer is too thin to be detected by XRD. With the increase of the amount of passivating agent, the permeability of powder decreases gradually and the performance of anti-DC-Bias loading improved. The core loss shows a trend that it decreases first and then increases with the increase of passivating agent dosage. If the amount of passivator is too much, the core loss will increase rapidly. When a 2% passivator is used, the magnetic permeability of the powder is 72, the DC-Bias characteristic is 51.3% with 100 Oe, and the core loss is 57 mW cm−3 at 100 kHz and 50 mT.

Design and evolution of Fe–Si–Al soft magnetic composites doped with carbonyl iron powders: Overcoming the restrictive relation between permeability and core loss

Herein, Fe–Si–Al-based soft magnetic composites (SMCs) doped with carbonyl iron powders (CIPs) at different concentrations were successfully prepared. The reaction between CIPs and core–shell Fe–Si–Al/SiO2 heterogeneous composite powders, induced by the high temperature and concentration gradient during heat treatment, was investigated. The effect of doping CIPs at different concentrations on the microstructure and magnetic properties of Fe–Si–Al-based SMCs was also studied. During heat treatment, the Fe–Si–Al/SiO2 powders inside the SMCs exhibited a complex reaction with the doped CIP. The reaction involved multidirectional migration of Al and Si, evolution of an Al2O3 + SiO2-composite insulating layer and formation of composite ferromagnetic phases. Furthermore, the density, saturation magnetisation, permeability and core loss of Fe–Si–Al-based SMCs were improved by doping the composites with moderate amounts of CIPs. The Fe–Si–Al-based SMCs doped with 8-wt% CIPs exhibited the best comprehensive magnetic properties (permeability = 43.5, saturation magnetisation = 160.1 emu/g and core loss = 481.7 kW/m3 at 10 mT and 100 kHz). Compared with undoped Fe–Si–Al-based SMCs, the permeability and saturation magnetisation increased by 40.3% and 24.0%, respectively, and the core loss decreased by 18.8%. Thus, the proposed method can effectively address the restrictive relation problem between permeability and energy loss in these composites.

High-performance Fe–Si soft magnetic composites with controllable silicate/nano-Fe composite coating

The design of magnetic insulation coating structure has always been a challenge for high-performance soft magnetic composites (SMCs). In this work, we prepared Fe–Si SMCs with silicate/nano-Fe composite coating successfully by in-situ oxidation method combined with spark plasma sintering (SPS). The formation mechanism of the composite coating and its effect on the electro-magnetic properties of Fe–Si SMCs were investigated. The results showed that a uniform Fe2O3 coating can be obtained by reactions between Fe and H2O/O2 during in-situ oxidation process, and became thicker with the increased oxidation time. After sintering, the oxide coating was transformed into a composite coating composed of Fe2SiO4 with excellent insulation and nano-Fe with high ferromagnetism, which resulted from the interfacial reaction between Fe2O3 coating and Fe–Si core. The increased oxidation time led to the gradually thicker composite coating, and resulted in a linear decrease in saturation magnetization, indicating good controllability of the coating. However, excessive oxidation time led to the increased eddy current loss as well as the core loss due to the weakened resistivity. Thus, the Fe–Si SMCs exhibited high saturation magnetic induction (1.66T) and very low core loss (643.9 kW/m3 at 0.1 T/50 kHz) especially when the oxidation time was 1 h.

High-performance FeSiAl soft magnetic composites achieved by confined solid-state reaction

Soft magnetic composites (SMCs) consisting of insulated metallic magnetic particles are critical materials in modern electronics. However, the simultaneous optimization of power loss and permeability for SMCs remains challenging due to the vulnerable insulation layer inside. Here, we succeed in fabricating FeSiAl SMC by confined solid-state reaction between TiO2 and FeSiAl matrix, which leads to the formation of homogeneous and lattice-matched Al2O3 layer and brings about effective electrical insulation of FeSiAl particles. TiO2 can progressively release O atoms and confine the solid-state reaction strictly within the interfacial region. Meanwhile, itself becomes ferromagnetic with deficient oxygen, resulting in alleviated magnetic dilution. Fast domain wall displacement and small hysteresis loss are directly observed by in-situ Lorenz transmission electron microscopy. The obtained FeSiAl SMC exhibits low power loss of 130 mW·cm−3 (50 mT, 100 kHz) and high effective permeability of 143, which is desired in energy-saving and high-efficiency devices. This work relates the interfacial behavior with magnetic properties and highlights a new strategy for fabricating high-performance SMCs.

Microstructure and magnetic properties of the FeSiAl soft magnetic composite with a NiFe2O4-doped phosphate insulation coating

Novel FeSiAl soft magnetic composites (SMCs) with a phosphate insulation coating doped with magnetic NiFe2O4 nanocrystalline particles were prepared. They exhibited high permeability, ultra-low loss, and high thermal stability. The saturation magnetization of the FeSiAl SMC increased, while the coercivity decreased due to the exchange coupling of the magnetic nanocrystalline particles. The total loss of the novel SMC decreased to 139.93 kW/m3 at 100 mT and 100 kHz, which is only one-third of that of common commercially available Sendust composites, while the permeability was up to 62 for the reduced demagnetization field. Furthermore, three-dimensional loss separation was performed based on the nonlinear regression method, and the complex permeability was separately addressed as the domain-wall movement and spin resonance parts. The minimum total loss was ascribed to the significantly reduced hysteresis loss and the slightly reduced eddy current loss, corresponding to the low coercivity (Hc = 0.341 Oe) and high impedance (|Z| = 67.1 MΩ). This was attributed to the improved magnetic properties and resistance of the insulation coating, which was related to the magnetic nanoparticles embedded in the insulation coating. The permeability was mainly derived from the spin resonance due to the complete insulation coating and ultrafine particles. This novel SMC with a phosphate insulation coating doped with magnetic NiFe2O4 nanocrystalline particles provides a high-efficiency, high-frequency, and high-saturation soft magnetic device for switching power supplies, photovoltaic inverter boost inductors, and other applications.

Improvement in core losses for FeSiAl soft magnetic composites induced by powder annealing treatment

In this study, low-loss FeSiAl soft magnetic composites (SMCs) were prepared through atomic layer deposition coating and high temperature annealing for FeSiAl ferromagnetic powder, combined with subsequent bonding, pressing and sintering processes. Microstructural analysis indicated that a thin, dense, and continuous Al2O3 coatings deposited onto the FeSiAl surfaces could withstand an annealing temperature of up to 1000 °C, and high temperature annealing for powder has been proved to improve the magnetic properties of SMCs effectively. The hysteresis loss of FeSiAl SMCs was significantly improved because the integrity of the coating layer facilitated grain growth and stress relaxation at high temperatures. Meanwhile, the coating layers with high resistivity confined eddy currents inside the powders and reduced eddy current loss. What's more, the permeability was also improved due to the relaxation of residual stresses and the reduction of structural defects. Compared with that of raw FeSiAl SMC, the permeability of the SMC prepared via powders annealing at 1000 °C increased from 69.27 to 73.48, and its core loss decreased from 261.9 to 145.7 mW/cm³ (100 mT/50 kHz). However, for the SMC annealed at 1100 °C, the eddy current losses increased sharply because of the partially decomposed Al2O3 coating. Notably, the magnetic performance (principally core loss) of the FeSiAl SMCs could be modulated by varying the annealing temperature. This study provides a novel strategy for reducing the core loss of FeSiAl SMCs through powder annealing.

Sodium Nitrate Passivation as a Novel Insulation Technology for Soft Magnetic Composites

Sodium nitrate passivation has been developed as a new insulation technology for the production of FeSiAl soft magnetic composites (SMCs). In this work, the evolution of coating layers grown at different pH values is investigated involving analyses on their composition and microstructure. An insulation coating obtained using an acidic NaNO 3 solution is found to contain Fe 2 O 3 , SiO 2 , Al 2 O 3 , and AlO(OH). The Fe 2 O 3 transforms into Fe 3 O 4 with weakened oxidizability of the NO 3 – at an elevated pH, whereas an alkaline NaNO 3 solution leads to the production of Al 2 O 3 , AlO(OH), and SiO 2 . Such growth is explained from both thermodynamic and kinetic perspectives and is correlated to the soft magnetic properties of the FeSiAl SMCs. Under tuned passivation conditions, optimal performance with an effective permeability of 97.2 and a core loss of 296.4 mW∙cm −3 is achieved at 50 kHz and 100 mT.

Soft magnetic composites FeSiAl/MoS2 with high magnetic permeability and low magnetic loss

Choosing Two-Dimensional (2-D) layered semiconductor material MoS2 as the insulator, FeSiAl/MoS2 composites were synthesized by mixing MoS2 and aerosolized FeSiAl in a certain mass ratio. The structure, morphology and magnetic properties of FeSiAl/MoS2 composites were measured by XRD, SEM, XPS, VSM and B-H analyzer. The SEM results show that high-speed ball milling breaks the binding of weak Van der Waals force between MoS2 layers, and nano-thick MoS2 micron flakes wrapped on the FeSiAl spherical surface. The results of magnetic properties show that not only the FeSiAl/MoS2 composite achieves a higher magnetic permeability due to the thin MoS2 flakes clinging to the FeSiAl particle surface, but also the eddy current between the metallic particles is blocked, resulting in a great reduction of eddy current loss. The permeability results show that the relaxation frequency of FeSiAl/MoS2 composites exceeds 1 MHz, which is suitable for application at high frequency. The magnetic loss of FeSiAl/1 wt%MoS2 composite reaches 454kWm−3 under the condition of f= 0.1 MHz and B= 0.1 T, which is about three quarters of that of FeSiAl soft magnetic composites for commercial application.

Over 100 MHz cut-off frequency mechanism of Fe-Si soft magnetic composites

Soft magnetic composites of spherical Fe-5wt%Si particles insulated by epoxy resin are studied. The cut-off frequency increases from 7 MHz to 110 MHz by changing particle size from 116 μm to 24 μm. By applying a DC field to remove the displacement of domain wall and reversal magnetization of domain, the mechanism of cut-off frequency and permeability is discussed. Combining with the extended effective medium theory, the cut-off frequency and permeability in the range of MHz comes from the nature resonance modulated by eddy current. Weaking the effect of eddy current in magnetic particle is an effective way to increase the cut-off frequency of soft magnetic composites.

Reduction of core loss for FeSi soft magnetic composites prepared using atomic layer deposition-based coating and high-temperature annealing

Using atomic layer deposition and high-temperature annealing to fabricate coatings for Fe-6.5 wt%Si powder reduce the hysteresis losses of the resultant composites drastically without sacrificing the permeability properties, and keep the eddy current losses at a relatively low value. The core loss of annealed FeSi SMCs is 39.67% lower than that of composites prepared using raw Fe-6.5 wt%Si powder, meanwhile the permeability remains at relatively high value (at B = 100 mT, f = 50 kHz). The decreasing of the core loss is mainly attributed to hysteresis loss reduction caused by grain growth. And the low eddy current loss is guaranteed by the uniform, complete, compact coating layer formed the surface of FeSi particles, which transforms to a protective and insulating layer containing silicate and metal oxide after annealing. On the premise of ensuring the integrity of the insulation layer, the annealing temperature of powder is significantly increased by surface modification, so as to reducing the hysteresis loss meanwhile controlling the eddy current loss. • Low core loss Fe-Si soft magnetic composites were prepared. • Nano-Al 2 O 3 was deposited on the surfaces of Fe-Si powders by ALD. • A protective and insulating layer formed at the interface after annealing. • Hysteresis loss reduced obviously due to the grain growth. • Decline of hysteresis loss dominates the dramatic reduction of total loss.

Ultra-low core loss FeSiAl-based soft magnetic composites with ultra-thin MoO3 composite insulating layer

In this work, core/shell structured FeSiAl/MoO3 (spherical FeSiAl covered by ultra-thin MoO3 composite insulating layer) soft magnetic composites (SMCs) have been fabricated by a two-step heat treatment process. The influences of ammonium molybdate (AHM) content, first-step annealing temperature and second-step annealing temperature on magnetic, mechanical properties and electrical resistivity (ρ) have been comprehensively investigated. It is shown that the coating integrity and the thickness of MoO3 nanoparticles layer can be regulated by the content of AHM, leading to the improvement of ρ. Moreover, composite insulating layer with the thickness of 47 ± 8 nm is formed and completely coated on FeSiAl particles with 15 wt% AHM, resulting in the fact that the highest radial crushing strength (K = 62.3 MPa) and lowest core loss (Pcv = 128.8 mW/cm3) is obtained. In addition, Pcv is separated into two components: hysteresis loss component and eddy current loss component. Further studies display that eddy current loss is only half of hysteresis loss. As a result, the FeSiAl SMCs with 47 ± 8 nm MoO3 composite insulating layer possess the lowest core loss of 128.8 mW/cm3 at 50 mT/100 kHz. The low core loss of the FeSiAl/MoO3 SMCs with ultra-thin composite insulating layer has a great potential in the fields of conversion and power transmission.

Multifunctional FeSiAl Soft Magnetic Composites with Inorganic–Organic Hybrid Insulating Layers for High Mechanical Strength, Low Core Loss and Comprehensive Anti-Corrosion

Multifunctional FeSiAl Soft Magnetic Composites with Inorganic–Organic Hybrid Insulating Layers for High Mechanical Strength, Low Core Loss and Comprehensive Anti-Corrosion

Enhanced magnetic properties of FeSiAl soft magnetic composites prepared by utilizing phosphate: PSA as insulating layer

Enhanced magnetic properties of FeSiAl soft magnetic composites prepared by utilizing phosphate: PSA as insulating layer