Iron-based Soft Magnetic Composites Research Articles

Influence of Polytetrafluoroethylene Content, Compaction Pressure, and Annealing Treatment on the Magnetic Properties of Iron-Based Soft Magnetic Composites.

To improve the magnetic properties of iron-based soft magnetic composites (SMCs), polytetrafluoroethylene (PTFE) with excellent heat resistance, electrical insulation, and extremely high electrical resistivity was chosen as an insulating coating material for the preparation of iron-based SMCs. The effects of PTFE content, compaction pressure, and annealing treatment on the magnetic properties of Fe/PTFE SMCs were investigated in detail. The results demonstrate that the PTFE insulating layer is successfully coated on the surface of iron powders, which effectively reduces the core loss, increases the resistivity, and improves the frequency stability and the quality factor. Under the combined effect of optimal PTFE content, compaction pressure, and annealing treatment, the iron-based SMCs exhibit a high effective permeability of 56, high saturation magnetization of 192.9 emu/g, and low total core losses of 355 mW/cm3 and 1705 mW/cm3 at 50 kHz for Bm = 50 mT and 100 mT. This work provides a novel insulating coating layer that optimizes magnetic properties and is advantageous for the development of iron-based SMCs. In addition, it also provides a comprehensive understanding of the relationship between process parameters and magnetic properties, which is of great guiding significance for scientific research and industrial production.

Preparation and Magnetic Properties of Low-Loss Soft Magnetic Composites Using MgO-Phenolic Resin Coating.

Optimizing the interface between a magnetic powder matrix and an oxide-insulating layer is an effective method to improve the permeability and lower eddy current loss of iron-based soft magnetic composites. In this study, in order to improve the bonding strength of the substrate and insulation layer, soft magnetic composites were prepared by pressing and heat treating with reduced iron powder as a magnetic matrix, high-temperature MgO nanoparticles as insulating coating, and phenolic resin as an adhesive. The effects of MgO content on the microstructure and magnetic properties of the composites were investigated. The results of a scanning electron microscopy and an energy-dispersive spectrometer analysis corroborate that the results obtained regarding the frequency characteristics and the resistivity of the iron powder agree with the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis and confirm their improvement by the presence of an insulating layer of MgO. The resistivity of the sample coated with 4 wt.% MgO is nearly 45 times higher than that of the uncoated sample under the same conditions. The MgO-insulating film formed on the surface of iron powder makes the coated sample have low effective grain size, high resistivity, and low magnetic loss at a high frequency. At 1 kHz, the magnetic loss of the 4 wt.% MgO-coated sample is reduced by 77.3%, and the magnetic loss is only 5.8% compared with the uncoated sample at 50 kHz. This magnetic loss separation study shows that the addition of MgO insulation material can effectively reduce the eddy current loss of the magnetic powder core. The 4 wt.% MgO-coated sample has the lowest hysteresis loss factor and relatively low eddy current loss factor, so it can be determined that the addition of 4 wt.% MgO is the optimum content to attain a low magnetic loss.

MHz cut-off frequency and permeability mechanism of iron-based soft magnetic composites

Abstract The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments. Here, a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported. The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring, the distribution of particles, and the particle size. The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect. An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data. This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.

Improved permeability and core loss of iron-based soft magnetic composites prepared by interface diffusion of nitrogen atoms

The magnetic properties of SMCs are typically challenging to further enhance, after compaction into a specific shape. However, in this study, a gas-nitriding process is employed to diffuse nitrogen atoms into iron-based magnetic toroidal after being prepared, resulting in an improvement in effective permeability and reduction in core losses. The results indicate that the saturation magnetization decreases with increasing nitriding time, reaching its minimum value at a nitriding time of 24 h, where Ms measure at 199.8 emu/g. The sample nitrided for 12 h exhibits superior effective permeability, high-frequency stability, DC-bias property, and total core loss, indicating its suitability for high-frequency applications. The gas-phase nitride process can further enhance the performance of the prepared soft magnetic composites, which is of significant value in scientific applications.

Hydroxyethylidene-1,1-diphosphonic acid surface treatment as insulation technology for iron based soft magnetic composites

In this study, we employed HEDP surface treatment as an insulation coating technology for the preparation of iron-based soft magnetic composites. The coating layer primarily comprises metal chelate, alongside minor quantities of iron oxides and hydroxides. The influence of treatment time on the microstructure, corrosion resistance and electromagnetic properties of the soft magnetic composites is investigated. The findings indicate a substantial enhancement in the corrosion resistance of iron powder treated with HEDP, and the iron powder subjected to a 90-minute treatment exhibited the most uniform and dense coating, yielding optimal magnetic properties. Notably, the sample's loss after a 90-minute treatment is recorded at 360.6 mW/g, indicating a remarkable reduction of 66.88 % when compared to the untreated sample. This research offers a straightforward and cost-effective approach for the industrial-scale production of soft magnetic composite materials with exceptional magnetic characteristics.

Design, fabrication, and magnetic properties of iron-based soft magnetic composites with La2NiMnO6 ferromagnetic insulation layer

In this work, La2NiMnO6, which exhibits a remarkably unique combination of ferromagnetic properties and high resistivity, was employed as an insulation coating to improve the magnetic properties of iron-based soft magnetic composites (SMCs). La2NixMn2-xO6 (x = 0.4–1.6) were synthesized via the sol-gel method at different temperatures (500–700 °C). The optimal crystallinity and magnetic properties were observed at 700 °C with x = 1, thus La2NiMnO6 synthesized under these specific conditions was utilized as an insulation coating medium. With the increase of La2NiMnO6, the saturation magnetization of La2NiMnO6/Fe SMC gradually decreases; however, this decrease is minimal due to the inherent ferromagnetic properties of La2NiMnO6. As La2NiMnO6 increases, the effective permeability of La2NiMnO6/Fe SMC initially increases and then decreases, while the core loss initially decreases and then increases. The highest effective permeability and lowest core loss are achieved at a coating amount of 1.2 wt%. As the operating temperature increases from −40 °C to 100 °C, the permeability gradually increases while losses decrease, making it suitable for use as a power device.

Preparation and Magnetic Properties of AlN/Phenolic Resin-Coated Iron-Based Soft Magnetic Composites

Preparation and Magnetic Properties of AlN/Phenolic Resin-Coated Iron-Based Soft Magnetic Composites

Energy loss and hysteresis of reversible magnetization processes in iron-based soft magnetic composites

The paper focuses on investigation of the hysteresis originating from the reversible magnetization processes and the quantification of the corresponding energy dissipation, on soft magnetic composite materials differing in various parameters so exhibiting different proportions of magnetization processes types during quasi-static magnetizing reversal under different maximum inductions. It was confirmed that reversible magnetization processes show hysteresis too and generate energy losses. These losses come from frictional effects accompanying local rotations of spins at the microscopical view of all magnetization processes including the reversible ones. It was found that the area of a hysteresis loop obtained by the integration of reversible permeability reveals approximately the proportion of reversible magnetization vector rotations, which produce energy loss much more than reversible domain wall displacements.

Magnetic properties of Fe/parylene soft magnetic composites prepared via chemical vapor deposition

Iron-based soft magnetic composites with different contents of parylene were prepared by chemical vapor deposition (CVD), though this method, the edges and spikes can be coated with parylene. The morphology and magnetic properties of the materials are investigated. The self-lubricating parylene forms a thin and uniform insulating layer on the surface of iron particles, which reduces the magnetic loss of soft magnetic composite materials. The 4% parylene coated iron powder has high compression density, low hysteresis loss, excellent insulation performance, high resistivity and low eddy current loss. Compared with silicone resin and epoxy resin, the insulating layer formed by prylene has fewer holes and gaps, and the magnetic core loss is smaller.

Effect of Various Metal Oxide Insulating Layers on the Magnetic Properties of Fe-Si-Cr Systems

Iron-based soft magnetic composites (SMCs) are the key components of high-frequency electromagnetic systems. Selecting a suitable insulating oxide layer and ensuring the integrity and homogeneity of the heterogeneous core–shell structure of SMCs are essential for optimizing their magnetic properties. In this study, four types of SMCs—Fe-Si-Cr/ZrO2, Fe-Si-Cr/TiO2, Fe-Si-Cr/MgO, and Fe-Si-Cr/CaO—were prepared via ball milling, followed by hot-press sintering. The differences between the microscopic morphologies and magnetic fproperties of the Fe-Si-Cr/AOx SMCs prepared using four different metal oxides were investigated. ZrO2, TiO2, MgO, and CaO were successfully coated on the surface of the Fe-Si-Cr alloy powders through ball milling, forming a heterogeneous Fe-Si-Cr/AOx core–shell structure with the Fe-Si-Cr alloy powder as the core and the metal oxide as the shell. ZrO2 is relatively hard and less prone to breakage and refinement during ball milling, resulting in a lower degree of agglomeration on the surface of the composites and prevention of peeling and collapse during hot-press sintering. When ZrO2 was used as the insulation layer, the magnetic dilution effect was minimized, resulting in the highest resistivity (4.2 mΩ·cm), lowest total loss (580.8 kW/m3 for P10mt/100kHz), and lowest eddy current loss (470.0 kW/m3 for Pec 10mt/100kHz), while the permeability stabilized earlier at lower frequencies.

Improved permeability and decreased core loss of iron-based soft magnetic composites with YIG ferrite insulating layer

In this study, single-phase yttrium iron garnet (YIG) ferrite was synthesized by sol-gel method, which was firstly used as the insulating layer to prepare Fe/YIG soft magnetic composites (SMCs). It was demonstrated that the Fe powders were uniformly coated with the YIG ferrite for the Fe/YIG SMCs. The influence of the YIG content on the soft magnetic properties of the Fe/YIG SMCs were investigated in detail, the results showed that the total core loss (Pcv) of all Fe/YIG SMCs were smaller than pure Fe. The Pcv firstly decreased with increase of the YIG content up to 1.0 wt% (Pcv=2460 mW/cm3, 4 mT/590 kHz), then increased with the increase of YIG from 1.0 wt% to 5.0 wt%. What’s more, the effective permeability (μe) of the Fe/YIG SMCs with YIG from 1.0 wt% to 3.0 wt% were higher than that of Fe, confirming both decreased core loss and improved permeability were accomplished in the Fe/YIG SMCs, which demonstrated that the YIG ferrite has good application prospects as new coating layer for SMCs used in medium to high frequency environments.

Effect of annealing on magnetic properties of iron-based soft magnetic composites with iron oxide insulator

This study introduces a closed oxidation system for forming an oxide insulating film on the surface of pure-iron powder, using an oxygen concentration analyzer to monitor the progress of the reaction. The closed system is designed such that all the supplied oxygen completely reacts to form an oxide film at 500 ℃. It is established that the oxide-film thickness can be controlled by the quantity of oxygen supplied. XRD analysis indicates that the oxide film is mostly composed of the Fe3O4 phase. The TEM oxygen mapping image shows that the oxide film is uniformly and completely formed on the surface of pure-iron powder. Further, toroidal cores are fabricated by compacting the pure-iron powder coated with an oxide insulating film. To relieve the strain generated during compaction, annealing is performed in the 400–700 ℃ range. At annealing temperatures below 550 ℃, the change in the core loss is not considerable (85.0 W/kg at room temperature (23 ℃) and 94.8 W/kg at 550 ℃). However, above 550 ℃, sudden increase in the core loss is observed (505.9 W/kg at 700 ℃). The Fe3O4 in the oxide film reacts with the Fe phase to form FeO above 570 ℃, which is the eutectoid temperature. This phase transformation damages the insulation of the oxide film, resulting in a sharp increase in the eddy current loss. The hysteresis loss decreases from 71.2 W/kg to 43.9 W/kg with the increase in the annealing temperature. It is determined that the pure-iron powder core coated with an oxide insulating film is heat-resistant up to a temperature of 550 ℃.

Preparation of FeNiMo/SiO<sub>2</sub> composite core and regulation of soft magnetic properties

Nowadays, metal soft magnetic materials are mainly used in electronic components such as high-frequency inductors. Since all the elements in the soft magnetic alloys are transition metals, dense oxide layer is easily formed on their surfaces, which can affect the regulation of soft magnetic properties. In order to solve the problems, in this work, an innovative high-temperature pretreatment process in H<sub>2</sub>/Ar mixture is adopted to pretreat FeNiMo raw powders. We confirm that the high temperature treatment in reducing atmosphere can effectively remove metal oxides from the FeNiMo material surface and increase the content of elemental states, thereby further significantly improving the effective permeability of FeNiMo raw powders. The pretreated FeNiMo powder is evenly coated with SiO<sub>2</sub> layers, forming the FeNiMo/SiO<sub>2</sub> soft magnetic composites. Compared with the untreated FeNiMo powder coated with SiO<sub>2</sub>, the FeNiMo/SiO<sub>2</sub> pretreated with H<sub>2</sub>/Ar mixture gas at high temperatures has high effective permeability and low loss. Our FeNiMo/SiO<sub>2</sub> cores prepared by the synergistic effect of high-temperature pretreatment process in H<sub>2</sub>/Ar mixture and insulation coating process have more excellent soft magnetic properties than other iron-based soft magnetic composites. Therefore, the insulation coating after being pretreated at high temperature in reducing atmosphere can greatly improve the permeability and reduce the core loss of soft magnetic composites. This will provide a new strategy for enhancing the soft magnetic properties of the composite cores.

Improved Permeability and Decreased Core Loss of Iron-Based Soft Magnetic Composites with Yig Ferrite Insulating Layer

Improved Permeability and Decreased Core Loss of Iron-Based Soft Magnetic Composites with Yig Ferrite Insulating Layer

Iron-Based Soft Magnetic Composites Fabricated by Laser Additive Manufacturing

Iron-Based Soft Magnetic Composites Fabricated by Laser Additive Manufacturing

Improved magnetic properties of iron-based soft magnetic composites with a double phosphate-SiO2 shells structure

Improved magnetic properties of iron-based soft magnetic composites with a double phosphate-SiO2 shells structure

Improved high-frequency performance of iron-based soft magnetic composites with Co2Z-type hexaferrites

Co2Z-type hexaferrites were synthesized with sol–gel method, and then were composited with pure iron powders to form a new type of iron-based soft magnetic composites (SMCs). The morphology, components and magnetic properties of all samples were characterized by XRD, SEM, EDS, B-H Analyzer and DC Current Source. All results indicate that Co2Z-type hexaferrites are well dispersed in the SMCs and play the role of insulation. Fe/Co2Z SMCs with the high Ms and low Hc present the higher effective permeability, lower core loss at high frequencies and more stable D-C bias characteristics than the pristine Fe SMCs. All results indicate that Co2Z hexaferrites with the high resistance could effectively improve the high-frequency performance of Fe/Co2Z SMCs.

Magnetic and Mechanical Properties of Iron-Based Soft Magnetic Composites Coated with Silane Synergized by Bi2O3

Magnetic and Mechanical Properties of Iron-Based Soft Magnetic Composites Coated with Silane Synergized by Bi2O3

Magnetic properties of iron-based soft magnetic composites prepared via phytic acid surface treatment

In this study, phytic acid (PA) surface treatment was used to prepare iron-based soft magnetic composites (SMCs). The composition and microstructure of the SMCs were analyzed to assess changes in the magnetic properties. As the treatment time increased, the insulating layer on the powder surface gradually thickened, changing the internal morphology and conductive path of the annular samples after compacting. The changes in the magnetic properties and core loss were attributed to the increased resistivity and enhancement of the magnetic dilution effect. The optimal soft magnetic performance (μm = 389, Pt = 235.1 mW/g measured at 100 kHz and 50 mT) was obtained by adjusting the processing time. This reduces the loss by 52.96% compared to the untreated sample and improves the application potential of soft magnetic composites at medium and high frequencies.

Communication—Magnetic Properties of Fe/Na2SiO3/Fe3O4 Soft Magnetic Composite by Two-Stage Ball Milling

Iron-based soft magnetic composites (SMCs) were prepared by two-step ball milling with sodium silicate and ferroferric oxide. The presence of the precoated silicate layer has increased the resistivity of the powder surface, which also improved the agglomeration of ferroferric oxide. The addition of magnetic ferroferric oxide improves the dilution effect. Combining the advantages of both sodium silicate and ferroferric oxide, the prepared soft magnetic composite material has excellent performance. After annealing at 400 °C, the core loss is 214.5 W Kg−1 (1 T, 1000 Hz), and the saturation magnetic induction is 1.33 T.