Fe-based Soft Magnetic Composites Research Articles

Wide induction range analysis of DC magnetic properties and magnetization processes of Fe-based soft magnetic composites

The paper presents systematic analyses of a wide maximum induction range (0.001 T–1.4 T) DC magnetic properties of iron-based soft magnetic composite (SMC) materials by applying different methods to understand the specific features of magnetization reversal of this increasingly popular class of soft magnetic materials, including a hitherto less explored area of the Rayleigh region of very low magnetic fields, which has growing application potential in new, low-energy consuming electronic devices or ultra-low magnetic field shielding. The total permeability, coercive field and remanent magnetic induction were analysed in connection with the reciprocity factor and inner demagnetization factor and their relations to interparticle magnetic interaction, domain wall movability and predominance of individual magnetization processes. Their dependence on the magnetic induction and the properties of each sample were revealed and confirmed also by energy loss separation. The Rayleigh region analytical expressions for the coercive field, remanent magnetic induction, the ratio of irreversible to reversible magnetization changes and their percentages within the magnetizing cycle were used for SMCs for the first time.

Unprecedented heat resistance of Fe-based soft magnetic composites realized with tunable double insulation layer: Synergy of MgO diffusion barrier and void-filling SiO2 layer

Soft magnetic composites (SMCs) comprising surface-insulated Fe powders have attracted significant attention owing to their capability of producing innovative three-dimensional cores with high magnetic flux density and their potential utilization in various electrical machinery fields. The aim of this study is to fabricate SMCs with an inorganic double insulating layer, which can substantially enhance heat resistance and enable enhanced magnetic and mechanical performance through high-temperature annealing. Herein, SMCs with different inorganic coating materials (single layers of SiO2, MgO, and PO4 and double-layers of MgO and SiO2) were prepared by a sol–gel method and powder compaction. In particular, a certain double-layered SMC core (Fe@MgO@SiO2) exhibited retention of internal insulation matrix even after annealing at 900 °C and a significantly suppressed core loss owing to synergistic effects of a diffusion barrier in the primary layer and an electrical insulator in the secondary layer. As anticipated, high-temperature heat treatment at > 700 °C reduced coercivity, which enhances permeability and hysteresis loss of SMCs. The double-layered SMCs also showed an increase in flexural strength of 280% when the annealing temperature was increased from 600 to 900 °C.

High density Fe-based soft magnetic composites with nice magnetic properties prepared by warm compaction

The influences of compacting temperature (Tc), molding pressure (Pm), contents of lubricant (Cl) and binder (Cb) on the compacted density (ρc) and its comprehensive soft magnetic properties for the FeSiCr soft magnetic composites (SMCs) fabricated by warm compaction were systematically studied. Appropriate increase of Tc is beneficial to improve the surface lubrication effect of magnetic powders during the forming process of SMCs, thus giving rise to the increase of ρc and the decrease of porosity fraction for the SMCs. Under this situation, the resistance of domain rotation and domain wall displacement in the SMCs during magnetization process is reduced, which is finally in favor of the improvement of SMCs’s soft magnetic properties. The results of loss separation show that the Ph value plays a dominant role in the variation trend of Pcv value for the FeSiCr-SMCs in the test frequency range of 20–200 KHz, wherein the ratio of Ph/Pcv is large than 81 %. Under the optimized process parameters of Tc= 110 ℃, Pm= 600 MPa, Cl= 1.5 wt. % and Cb = 2.5 wt. %, the ρc of FeSiCr-SMCs increases by 8.14 % to 6.38 kg/m3, and the SMCs exhibit better comprehensive soft magnetic properties compared with those at Tc = 25 ℃. Hereinto, μe increases by 19.89 % to 45.8 @ 100 kHz, Pcv decreases by 26.11 % to 495.8 kW/m3@f= 100 kHz, Bm= 50mT, and μe % reached 85.5 % at H = 8000 A/m. These results indicated that the warm compaction process is one of the effective ways to further promote Fe-based SMCs to meet the development requirements of high-frequency, miniaturization and high-power of electronic equipment.

Low Core Losses of Fe-Based Soft Magnetic Composites with an Zn-O-Si Insulating Layer Obtained by Coupling Synergistic Photodecomposition

The major method used to reduce the magnetic loss of soft magnetic composites (SMCs) is to coat the magnetic powder with an insulating layer, but the permeability is usually sacrificed in the process. In order to achieve a better balance between low losses and high permeability, a novel photodecomposition method was used in this study to create a ZnO insulating layer. The effect of the concentration of diethyl zinc on the formation of a ZnO insulating film by photodecomposition was studied. The ZnO film was best formed with a diethyl zinc n-hexane solution at a concentration of around 0.40 mol/L. Combined with conventional coupling treatment processes, a thin and dense insulating layer was coated on the surface of iron powder in situ. Treating the iron powder before coating by photodecomposition led to a synergistic effect, significantly reduced core loss, and the effective permeability only decreased slightly. An iron-based soft magnetic composite with a loss value of 124 kW/m3 and an effective permeability of 107 was obtained at the frequency of 100 kHz and a magnetic field intensity of 20 mT.

Efficient synthesis of TiO2-coated layer for Fe-based soft magnetic composites and their regulation mechanism analysis on magnetic properties

Efficient synthesis of TiO2-coated layer for Fe-based soft magnetic composites and their regulation mechanism analysis on magnetic properties

High performance of Fe-based soft magnetic composites coated with novel nano-CaCO3/epoxy nanocomposites insulating layer

In this paper, a novel type of nano-CaCO3/epoxy nanocomposites insulating layer for the FeSiCr/carbonyl-iron soft magnetic composites (SMCs) has been successfully developed. The novel inorganic/resin nanocomposites can greatly reduce the core loss of the SMCs while maintain other excellent magnetic properties. By optimizing the content of insulating layer, the FeSiCr/carbonyl-iron SMCs exhibits the lowest core loss of 466.5 ​mW/cm3 at a maximum magnetic induction of 50 ​mT and frequency of 100 ​kHz, which is greatly reduced by 24.2%, compared with the sample only coated by epoxy resin. Meanwhile, the effective permeability and quality factor remains high. In addition, the production process of the novel nano-CaCO3/epoxy nanocomposites insulating layer exhibits the advantages of simplicity, convenience and low cost compared with other ceramic coatings (Al2O3, MgO, SiO2, etc.) and surface nitride coatings, which is more suitable for the industrialization of molded inductors, and therefore has a variety of industrial application prospects.

High permeability and low core loss Fe-based soft magnetic composites with Co-Ba composite ferrite insulation layer obtained by sol-gel method

To balance the core loss and permeability of soft magnetic composites (SMCs), a Co-Ba composite ferrite insulation layer was employed to clad the surface of reduced iron powder by sol-gel method. The successful preparation of the honeycomb-like Co-Ba composite ferrite coating layer was verified by scanning electron microscopy (SEM), the composition of the coating was determined by X-ray diffraction (XRD), and the magnetic properties were tested with a B-H curve analyzer. BSEM images of the polished cross-section and core loss separation results confirmed that an excessively high annealing temperature causes the composite ferrite insulation layer to fail. A high effective permeability of up to 121 at 300 kHz and low core loss (Pcv) of 129 kW/m3 at 100 kHz and 0.02 T were obtained in prepared samples at the optimized annealing temperature of 500 °C. Subsequently, simulation analysis based on the Clausius-Maxwell formula model was used to confirm the feasibility of the enhancement on effective permeability in Fe@Co-Ba composite ferrite theoretically. The agreement between simulation and experimental results further indicated that a good balance between the core loss and permeability of Fe-based SMCs was achieved by Co-Ba composite ferrite cladding.

Highly improved middle to higher frequency magnetic performance of Fe-based soft magnetic composites with insulating Co2Z hexaferrites

Single-phase Co2Z hexaferrite with excellent middle to higher frequency performance was synthesized via the sol–gel method, and then were mechanically mixed with Fe powders and compacted to form toroidal Co2Z hexaferrites/Fe soft magnetic composites (Co2Z/Fe SMCs). After characterization with XRD, SEM, EDS, VSM and B-H Analyzer, the influence of Co2Z hexaferrites on the microstructures, AC and DC magnetic performance were investigated in detail. Air gaps between Fe powders are filled with Co2Z hexaferrites at the optimized content and the density of Co2Z/Fe SMCs increases. Co2Z hexaferrites effectively improve the soft magnetic performance of Co2Z/Fe SMCs at middle to higher frequency. The permeability and DC bias performance of Co2Z/Fe SMCs increased with the Co2Z hexaferrites content up to the maximum for 1 wt% Co2Z/Fe SMCs, and then decreased. While the changing trend of the core loss is opposite to the permeability and reaches the minimum for 1 wt% Co2Z/Fe SMCs. Co2Z hexaferrites not only increase the resistance of Co2Z/Fe SMCs and reduce the eddy-current loss, but also improve the interface microstructures and optimize the magnetic circuit of Co2Z/Fe SMCs.

Enhanced AC magnetic properties of Fe-based soft magnetic composites coated with an electrically insulated SiO2–ZrO2 layer

Enhanced AC magnetic properties of Fe-based soft magnetic composites coated with an electrically insulated SiO2–ZrO2 layer

Pulsed Magnetic Field Experiments in SMM and SMC Materials: New Questions About Its Properties and Applications

This article analyzes the magnetization rotation behavior of Fe-based soft magnetic materials and soft magnetic composites (SMMs and SMCs, respectively) samples. Room temperature measurements of the complex permeability until frequencies near 20 MHz and isothermal M(H) magnetization curves obtained from room to low temperatures (down to 20 K) show very similar soft magnetic behavior for both type of samples. Pulsed magnetic fields have been used to test their behavior under extreme conditions. Even with a substantial increase of the field variation sweeping rate and the temperature reduction (from 20 to 300 K) both types of materials keep their pronounced non-hysteretic behavior. However, zero field cooled-field cooled (ZFC-FC) curves with an applied field lower than 7.5 kOe show full irreversibility below room temperature, which indicates the existence of a broad distribution of barrier heights and seems to be in full contradiction with the obtained complex permeability and M(H) results. In this article, we aim to clarify this new and unexpected dual behavior. We suggest the existence of pinning barrier heights which are very sensitive to the variation of the magnetic field allowing the magnetization rotation with no losses while there are other barrier heights which need high values for the magnetic static fields to be removed when the temperature changes.

Influence of processed parameters on the magnetic properties of Fe/Fe3O4 composite cores

Fe powders coated with Fe3O4 insulating layers were synthesized by in-situ oxidization method, and then the Fe/Fe3O4 composite cores were prepared by a powder metallurgy procedure. The formation of Fe3O4 on the surface of Fe powders can effectively reduce the magnetic loss and enhance the high-frequency performance of magnetic cores. With the increase of pressing pressure, the permeability increased firstly and then decreased, while the magnetic loss shows the opposite law. The residual stress of the composites can be released more sufficient by increasing the annealing temperature, which leads to the increase in permeability; however, Fe3O4 will decompose into FeO when the annealing temperature rises to 570 °C, thus destroying the magnetic properties of Fe-based soft magnetic composites. The composite compressed at 800 MPa and annealed in argon at 500 °C for 2 h exhibits excellent magnetic performance, which presents high permeability (μ) of 56 (1 KHz), high saturation magnetization (Ms) of 219.2 emu/g, and low magnetic loss (P) of 30.5 w/kg (20 mT, 100 kHz).

Hybrid Phosphate-Alumina Iron-Based Core-Shell Soft Magnetic Composites Fabricated by Sol-Gel Method and Ball Milling Method

Novel Fe-based soft magnetic composites (SMCs) with hybrid phosphate-alumina layers were prepared by both sol–gel and ball-milling methods. The effects of the fabrication methods and the addition of Al2O3 particles on the microstructure and the soft magnetic performance of SMCs were studied. The formation of the hybrid phosphate-Al2O3 shell not only leads to the decrease of the total core loss, but also results in the reduction of the permeability and saturation magnetization. However, the degree of decrease caused by the different methods were not identical. The sample with 8% Al2O3 prepared by the sol–gel method showed the best magnetic performance, exhibiting a high-amplitude permeability (μa) of 85.14 and a low total core loss (Ps) of 202.3 W/kg at 50 mT and 100 kHz. The hysteresis loss factor and the eddy current loss factor were obtained by loss separation. The results showed that the samples with the same Al2O3 content prepared by different methods exhibited almost the same total core loss. However, the contribution of the hysteresis loss and the eddy current loss showed an obvious difference in behavior because of the change of the particle shapes and the refinement of the particle size during the ball-milling process.

Magnetic properties of selected Fe-based soft magnetic composites interpreted in terms of Jiles-Atherton model parameters

The paper presents the Jiles-Atherton model application to selected Fe-based soft magnetic composites (of different types prepared with the intention of verifying the model), with inner demagnetizing fields consideration implemented. The model fits experimental anhysteretic magnetization curves with very good accuracy, obtaining parameters: the effective domain density, the interdomain coupling and the average magnetic moment of effective domain. The parameters are interpreted in comparison to maximum total and differential permeability, inner demagnetization factor and hysteresis losses. The denser effective domain structure with stronger interdomain coupling is found for the decreasing ferromagnetic filler content and mean particle size, together with higher inner demagnetizing fields, leading to lower number of active magnetic objects, reflected by magnetic properties worsening. The relation of magnetic properties to interdomain coupling strength and effective domain density is specific for each ferromagnetic component of composite. The parameters absolute values are found remarkably different from bulk ferromagnets values in literature, pointing out the specific magnetization reversal of composites.

Effects of compaction and heat treatment on the soft magnetic properties of iron-based soft magnetic composites

Iron-based soft magnetic composites (SMCs) are promising substitutes for laminate steels in electromagnetic applications due to their excellent magnetic properties and productivity. However, the preparation process is a key factor in deciding the magnetic performance of SMCs. In this work, the Fe-based soft magnetic composites with improved soft magnetic properties were achieved by optimizing the compaction and the annealing process. Results showed that the core–shell structure of powders which would directly have an impact on the permeability and the core loss of the SMCs could be affected by the compaction and the annealing process. In addition, the magnetic properties were enhanced by tuning the microstructure. As a result, the optimal magnetic performance of the compact with high permeability and low total core loss was obtained. The real part of the permeability of the soft magnetic composites could reach a maximal value of 336.8 and a rather low core loss of 2.5 W Kg−1 (measured at 50 mT and 5 kHz). Therefore, soft magnetic composites with enhanced magnetic properties were obtained by optimizing the powder metallurgy (PM) process in this study.

Structure and magnetic properties of Fe-based soft magnetic composites with an Li–Al–O insulation layer obtained by hydrothermal synthesis

In this paper, Fe-based soft magnetic composites (SMCs) hydrothermally coated with lithium aluminum oxide (Li–Al–O) with better magnetic properties and lower core losses than Al2O3 coated layers have be investigated. The microstructure and composition of the coating and magnetic properties of the composites were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and B–H curve analyzer. Those results revealed that when Li2CO3 was added to the aluminum nitrate solution, the originally formed Al2O3 coating layer converted to a layer with a mixture of several lithium aluminum oxides. Fe-based SMCs coated with lithium aluminum oxide showed lower core losses, higher and stable effective permeability as compared with iron rings coated with Al2O3, especially in high frequency range of 100–300 kHz.

Fe-based soft magnetic composites with high permeability and low core loss by in situ coating ZnFe2O4 layer

Fe powder particles were coated with ZnFe2O4 layer by in situ oxidation and then mixed with epoxy-modified silicone resin. Soft magnetic composites were prepared by compaction and annealing treatment of the coated powders. The coating layer was analyzed using Lorentz transmission electron microscopy, scanning electron microscopy and energy-dispersive spectroscopy X-ray analysis. Their magnetic properties were determined using a vibrating sample magnetometer and an auto-testing system for magnetic materials (SY8258B-H/m). The results show that the samples prepared at 1200 MPa and 550 °C exhibited distinguished magnetic properties, with low core loss of 497 W/Kg (100 kHz, 50 mT) and high amplitude permeability of 63 whose frequency stability is up to 170 kHz. The Fe SMCs with excellent soft magnetic properties provide great potential for application of various fields such as transformers, sensors and electromagnetic actuation devices.

Low-loss and high-induction Fe-based soft magnetic composites coated with magnetic insulating layers

Abstract We have provided a new and simple coating strategy to fabricate high-performance metal-based magnetic composites exhibiting both high magnetic inductions and decreased core loss. High-purity submicron FeCo particles have been dispersed into silicone resin to form a magnetic insulating film, which is then coated uniformly on the particle surface of high-purity Fe powders with a particle size of 170 μm to form new-type Fe-based soft magnetic composites (SMCs). These insulated magnetic layers containing submicron FeCo particles in these Fe-based SMCs can maintain very high saturated magnetization (209 A·m2·kg−1) for the composites, and also result in their low core loss. For traditional metal-based SMCs, the low core loss is often obtained accompanying with seriously decreased magnetic inductions. In present work, both high magnetic inductions and decreased core loss in company with high compacted density are achieved in these Fe-based SMCs coated with magnetic insulating coating layers. Specifically, the extremely low eddy current loss occurring in these new Fe-based SMCs enables their latent applications in low-loss and high-power magnetic devices.

Influence of heat treatment on microstructures and magnetic properties of Fe-based soft magnetic composites prepared by co-precipitation method

Abstract Fe/(NiZn)Fe2O4 soft magnetic composites (SMCs) were prepared by the co-precipitation method using pure atomised iron powder and chloride as raw materials. The morphology and element content of coated powders were analysed using scanning electron microscopy and energy dispersive spectroscopy. Moreover, we used electron probe micro-analyser, X-ray diffraction and Raman spectrum to systematically investigate the effect of heat treatment temperature in argon on the microstructure of SMCs, including O element distribution, phase formation and internal stress. The results show that by increasing heated temperature, the oxygen content at the boundary of the SMCs increased and the internal stress release of SMCs was more complete. Moreover, non-magnetic FeO would be generated in SMCs when the heat treatment temperature reached 550 °C. We also discussed the relationship of heat treatment temperature and atmosphere with AC magnetic properties of the samples, including permeability, core loss and coercivity. The results indicate that the SMCs annealed at 450 °C in argon had the optimum magnetic performance (µ = 55.8, P cv = 12.2 kw/m3, H c = 22.6 A/m). At the heat treatment temperature of 500 °C, the argon-annealed samples presented better magnetic properties and higher frequency stability than air-annealed samples.

In-situ formation of Fe3O4 and ZrO2 coated Fe-based soft magnetic composites by hydrothermal method

In this paper, the soft magnetic composite was prepared using a powder metallurgy method with the Fe3O4 and ZrO2 co-coated iron powder which was synthesized though the in-situ hydrothermal method. Energy dispersive spectroscopy (EDS) coupled with X-ray photoelectron spectroscopy (XPS) revealed that the Fe3O4 and ZrO2 were uniformly coated on the surface of iron powders. The addition of ZrO2 in the coating effectively improves the properties of the soft magnetic composite. ZrO2 can further improve the insulating properties, and enhance the thermostability of the coating simultaneously which will lead to resistivity increase and eddy current loss decrease. By controlling the additive amount of zirconium cation and annealing temperature, high magnetic induction of 1.002 T (measured at 8000 A/m), relatively high permeability of 83 (measured at 100 kHz), and low total core loss of 255.2 W/kg (measured at 100 kHz and 50 mT) were achieved. The Fe@ZrO2&Fe3O4 SMCs show high electrical resistivity and saturation induction, which may be widely used in high speed electric motor, transformer, inductance and switching power supply.

Properties of Ni<sub>0.5</sub>Zn<sub>0.5</sub>Fe<sub>2</sub>O<sub>4</sub>/Fe<sub>76</sub>Si<sub>9</sub>B<sub>10</sub>P<sub>5</sub> Bulk Soft Magnetic Composites by Annealing Treatment

Iron-based amorphous alloys have attracted technological and scientific interests due to their excellent soft magnetic properties. In the present study, Ni0.5Zn0.5Fe2O4/Fe76Si9B10P5 soft magnetic composites cylinder of 15 mm diameter and 3 mm thickness was prepared by spark plasma sintering at the temperature of 780 K. The amorphous Fe-based soft magnetic composites Ni0.5Zn0.5Fe2O4/Fe76Si9B10P5 exhibited good magnetic properties after annealing treatment at temperature ranging from 643 K to 743 K. The beneficial effects of treatment under different temperatures were discussed in terms of the improved magnetic performance of Ni0.5Zn0.5Fe2O4/Fe76Si9B10P5 soft magnetic composites.