The influence of FeNi nanoparticles on the microstructures and soft magnetic properties of FeSi soft magnetic composites

In this work, a new type of FeSi/FeNi soft magnetic powder core (SMPC) was successfully fabricated by coating FeNi nanoparticles on the surface of FeSi micrometer powder. The effects of different contents of FeNi nanoparticles on the micromorphology, internal structures, and soft magnetic properties of SMPCs were studied. The results show that FeNi nanoparticles adhere to the surface of FeSi powder, which can effectively fill the air gap between FeSi powder and is beneficial to the compaction of the powder cores during the pressing process. Thus, the density of the SMPCs is increased. Compared to FeSi SMPCs, the comprehensive soft magnetic properties of FeSi/FeNi SMPCs have been greatly improved. When adding 15 wt% FeNi nanoparticles, the SMPCs exhibit excellent magnetic properties with high effective permeability (increased by 43.8 %) and low core loss (decreased by 22.1 %). The high performance FeSi/FeNi SMPCs prepared in this work are expected to be widely used in power choke coils, uninterruptible power supplies, and boosts and inverter inductors.     

Structural studies, magnetic properties and loss separation in iron–phenolicsilane soft magnetic composites

In this work, six different series of iron based soft magnetic composites are produced and studied: (1) passive iron powder; (2) passive iron powder-0.7% resin with coupling agent; (3) passive iron powder-0.7% resin without coupling agent; (4) passive iron powder-1.5% resin with coupling agent; (5) passive iron powder-1.5% resin without coupling agent; (6) pure iron-1.5% resin. The specimens were shaped as cylindrical rods and characterized by fourier transform infrared spectrometer (FTIR), energy dispersive analyzer (EDX), X-ray diffraction (XRD) and indutance capacitance resistance (LCR) meter. The results show that the hysteresis loss coefficient is close to each other for all the samples (0.0011 < k₂ < 0.0019), but the eddy current loss coefficient is higher for the passive-0.7% resin sample without coupling agent (k₃ = 0.005) in comparison with the other samples.     

Effect of magnetic properties in FeSi soft magnetic composites by low melting glass powder as adhesive and insulating agent

Journal of Materials Science: Materials in Electronics - FeSi/1wt% glass soft magnetic composites are prepared by mechanically mixing, compacting, and annealing, their morphology is examined by...     

Microstructure evolution and soft magnetic properties of Fe-based nanocrystalline soft magnetic composites coated with lubricant

Here, the influence of zinc stearate on the microstructure and soft magnetic properties of the Finemet nanocrystalline soft magnetic composites (NSMCs) was systematically investigated. The results demonstrate that the core loss (P_cv) decreases and the effective permeability (μ_e) increases of the NSMCs with increasing zinc stearate from 0 wt% to 2.0 wt%, which can be attributed to the reduction of residual stress during compaction. Further increasing zinc stearate up to 3.0 wt%, the P_cv increases sharply, while the μ_e shows a decreasing trend. It can be considered that the addition of excess lubricant decomposes to CO₂ during annealing, which deteriorates the magnetic properties. After annealing at 560 °C, a thin hybrid layer of only about 53.6 nm containing iron phosphate, ZnO, and SiO₂ is formed in the NSMCs with 2.0 wt% zinc stearate, which exhibits excellent soft magnetic properties such as low P_cv of 174 kW/m³ and high μ_e of 66.7 at B_m = 0.1 T for 50 kHz. In addition, loss separation has been carried out and suggests that the addition of lubricant mainly affects hysteresis loss in the total energy loss of NSMCs.     

Effects of processing upon the properties of soft magnetic composites for low loss applications

We have investigated the effects of processing variables and methods on the density, structure and magnetic properties of soft magnetic composite (SMC) materials primarily for use in low loss applications. Two commercially available SMC materials from Höganäs AB, Sweden were used throughout the study. The materials differed only in terms of the solid state lubricant incorporated in the powder. This was sufficient to affect the density of pressed samples. Both monotonic and cyclic pressing regimes were used to compact the materials, with pressures sufficiently large to control the bulk mechanical properties of the samples produced (Hardness typically 1.6 GPa). Samples were heat-treated to both relieve any stresses imposed during pressing, and to control the final composition through oxidation or non-oxidation processes. Magnetic properties were observed using a vibrating sample magnetometer and Barkhausen noise analyser and electrical properties determined using a micro-ohmmeter. Both magnetic and electrical properties were observed to be strongly dependent on sample density and heat treatment.     

Highly enhancing electromagnetic properties in Fe-Si/MnO-SiO2 soft magnetic composites by improving coating uniformity

Fe-Si/MnO-SiO₂ soft magnetic composites (SMCs) are prepared by sintering ball milled Fe-Si/MnO₂ core–shell structured composites. The correlation between the coating uniformity and electromagnetic properties have been investigated via adjusting ball milling parameters in detail. The results indicate that uniform MnO₂ coating can be transformed into MnO-SiO₂ composite coatings with high insulation due to the high temperature reaction between MnO₂ and Si. Agate ball is more effective than stainless steel ball to improve the uniformity of MnO₂ coating as well as the electromagnetic properties such as significantly higher resistivity, lower core loss and better frequency stability of permeability. Moreover, increasing the ball milling time from 4 h to 24 h can obviously improve the coating uniformity and thus result in the remarkable increase of the resistivity from 2.4 mΩ·cm to 356.9 mΩ·cm. And the core loss and dynamic loss decrease rapidly while the M_s shows a slight decline. When the ball milling time reaches 24 h, the Fe-Si SMCs exhibits superior magnetic properties such as high M_s (181.0 emu/g), very low core loss (361.5 kW/m³ at 100 kHz) and good frequency stability of permeability (65) from 50 Hz to 1000 kHz.     

镍锌铁氧体薄膜的显微结构和低温磁性质

通过溶胶凝胶甩膜工艺,在抛光的硅晶片(100)基底上制备出Ni0.5Zn0.5Fe2O4(NZF)薄膜并对其结构和磁性的测量结果进行了分析。薄膜表面平整,具有较好的单相结构,其颗粒平均粒径约30nm。制备的NZF薄膜厚度分别约90、120和180nm。实验结果表明,薄膜在低温下表现出自旋玻璃态行为。当外加磁场为7.96×103A/m时,NZF薄膜自旋冻结温度大约在Tf=140K,自旋冻结程度随薄膜厚度增加而降低。在40~300K之间,薄膜饱和磁化强度和矫顽力都随着温度增加而降低。NZF薄膜在T=40K处存在最大磁化强度。较薄薄膜在40K以下饱和磁化强度的降低是因为磁性颗粒表面自旋被部分冻结而导致的磁性离子相互间自旋耦合作用减弱的结果。     

Eddy current and total power loss separation in the iron–phosphate–polyepoxy soft magnetic composites

This work investigates the magnetic properties of iron–phosphate–polyepoxy soft magnetic composite materials. FTIR spectra, EDX analysis, distribution maps, X-ray diffraction pattern and density measurements show that the particles surface layer contains a thin layer of nanocrystalline/amorphous phosphate with high coverage of powders surface. In this paper, a formula for calculating the eddy current loss and total loss components by loss separation method is presented and finally the different parts of power losses are calculated. The results show that, the contribution of eddy current in the bulk material for single coating layer (k_b = 0.18) is higher in comparison with double coating layer (k_b = 0.09). Moreover, iron–phosphate–polyepoxy composites (P = 0.000004f²) have lower power loss in comparison with iron–phosphate composites (P = 0.00002f²).     

Formation mechanism and magnetic performance of Fe-Si soft magnetic composites coated with MnO-SiO2 composite coatings

Fe-Si soft magnetic composites (SMCs) coated with MnO-SiO₂ composite coatings were fabricated via sintering the ball milled Fe-Si/MnO₂ composite powders. The transformation mechanism from MnO₂ coating to MnO-SiO₂ composite coatings was studied. The effect of MnO₂ content on the microstructure and magnetic properties of Fe-Si soft magnetic composites has also been investigated systematically. The analysis results indicated that MnO₂ would be reduced to MnO by Si in the Fe-Si particles at 780.1 ℃. When the temperature reached 985.8 ℃, the generated MnO and SiO₂ would further combine to form 2MnO·SiO₂, finally forming the MnO-SiO₂ composite coatings. With the increase of the MnO₂ content from 0.0 wt% to 10.0 wt%, the MnO-SiO₂ composite coatings became thicker, thus the saturation magnetization and permeability decreased gradually. However, exorbitant MnO₂ content above 5.0 wt% would result in excessive in-situ Fe existed in the composite coatings and obvious reduction of Si content in the Fe-Si particles due to the above solid-state reactions. Therefore, the increasing trend of the resistivity was weakened. And the 5.0 wt% MnO₂ coated Fe-Si SMCs exhibited superior comprehensive performance such as high saturation magnetization (186.5 A·m²/kg), good permeability (71), low total core loss (362.6 mW/cm³ at 50 kHz).     

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

Herein a double shells structure was proposed to overcome the drawbacks such as poor heat resistance, incomplete insulation and high core loss coating of iron-based soft magnetic composites (SMCs) with single shell structure. The surface of the iron powder was coated with a double shells structure composed of an inner phosphate coating and an outer SiO₂ coating through phosphating and hydrolysis successively. Subsequently, the effects of different SiO₂ addition amount on the microstructure of iron powder and magnetic properties of SMCs were studied. The introduction of SiO₂ in the double shells structure inhibited the decomposition and failure of phosphating layer after being annealed at a high temperature. The iron powder coated with the phosphate-SiO₂ insulating layer was still effective after annealing in a N₂ atmosphere at 570 °C, achieving the purpose of eliminating residual stress and improving magnetic properties. The optimal process parameters were set at 0.2 wt% phosphoric acid and 0.5 wt% tetraethyl orthosilicate to fabricate the phosphate-SiO₂ double shells. The iron-based SMCs presented excellent magnetic properties with B_s of 1.29 T and P_s of 169.2 W/kg (measured at 1 T and 1 kHz). In addition, the core loss of SMCs introduced with SiO₂ is 83% lower than that of SMCs produced by the phosphating process. This paper provides a feasible method for improving the magnetic properties of SMCs.

     

高能球磨法合成纳米晶NiZn铁氧体的结构和磁性

报告了作者利用机械球磨方法成功制备纳米晶NiZn铁氧体软磁材料的实验结果。实验样品具有很好的单相结构,所形成材料典型晶粒尺度为10～50nm。结合纯Fe3O4球磨样品,初步估算其样品的合成效率大约为27%～44%,这一结果可利用两步合成及中间纳米颗粒的高活性给予理解。对本实验利用球磨方法直接获得的NiZn铁氧体样品表现出较低的磁化强度σm和较大的矫顽力Hc,其典型值为43Am2kg-1和377×103(4π)-1A/m。从实用化角度而言,必要的热处理将是必要的。实验进一步证明,除了传统的机械合金化制备纳米晶软磁合金材料以外,利用高能球磨制备纳米晶NiZn软磁铁氧体也将是一种有效可行的新方法。     

磷化工艺对铁基软磁复合材料电磁性能的影响

研究了磷化工艺对铁基软磁复合材料电磁性能的影响。XRD、SEM、EDS分析和元素面分布结果表明,合适的磷化工艺能在铁粉表面生成1层很薄的非晶或纳米晶结构磷酸盐,并且包覆完整均匀。磁性能测量结果表明,室温条件下用0.01g/mL磷酸对铁粉进行磷化30min,所得到的磷化铁粉磁芯具有优异的综合电磁性能。随着磷酸浓度的增大,磷化时间的增长和磷化温度的提高,软磁复合材料磁芯的电阻率增大,中高频磁损耗不断降低,同时磁导率也有一定程度的降低。     

交换耦合软/硬磁双层膜体系磁动力学性质的研究

基于Laudau-Lifshitzt方程,在一维原子链模型的框架内研究了交换耦合软/硬磁双层膜体系的磁动力学性质,得到了软磁层在磁反转前处于一致磁结构和交换弹性磁反转过程中处于螺旋磁结构时的本征自旋波模式的频率及其空间分布特点,以及自旋波色散关系曲线。研究表明,软磁层的反磁化机制与自旋波的软模现象有密切关系,一阶自旋波模式的软化诱导了软磁层的磁反转,且磁反转的形式与一阶自旋波模式的空间分布状态相关。由磁动力学方法得到的磁反转临界场与近似的解析解得到的结果一致。     

Structure and magnetic properties of soft organic ZnAl-LDH/polyimide electromagnetic shielding composites

The imidization mechanism, structure, and magnetic properties of organic modified Zinc-aluminum layered double hydroxides/polyimide composites are investigated. During imidization, organic modified Zinc-aluminum layered double hydroxides lose the hydroxyl group and sodium dodecyl sulfate modifier decomposes partly resulting in a loose contact between PI and oxidized Zinc-aluminum layered double hydroxides. The thermal properties of composites are slightly decreased with increasing organic modified Zinc-aluminum layered double hydroxides but the wettability varies oppositely. Comparing to organic modified Zinc-aluminum layered double hydroxides, the saturated magnetization of heated organic modified Zinc-aluminum layered double hydroxides is enhanced slightly due to structural improvement in Fe₃O₄ crystalline domain. Therefore, the magnetic properties are not affected by imidization procedure. The soft magnetic composites have large potential in electromagnetic shielding.     

Crystallization mechanism and its correlation with structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys

Correlation of crystallization mechanism with the structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys has been investigated on the basis of Johnson–Mehl–Avrami kinetic model, transmission electron microscopy, and extended random anisotropy model. Pre-existent α-Fe clusters in melt-spun alloys with a size much smaller than critical nucleus size crystallize at a steadily increasing nucleation rate owing to the chain effect of rising constituent fluctuation. This unique crystallization mechanism leads to the formation of fine and uniform nanocrystallites and therefore superior soft magnetic properties. In contrast, pre-existent α-Fe clusters with a size approximate to the critical nucleus size nucleate gradually at the initial stage of crystallization process driven by thermal activation over the energy barrier of nucleation, and pre-existent α-Fe nanocrystallites with a size larger than critical nucleus size grow directly at the initial stage of crystallization process. Grains formed at the initial stage enlarge further in the subsequent crystallization process, which gives rise to a continuous decrease of the nucleation rate and the deterioration of soft magnetic properties.     

The improved magnetic properties of FeSi powders cores composed with different size particles

Journal of Materials Science: Materials in Electronics - FeSi powder cores are prepared by cold pressing the mixture of 200 mesh and 400 mesh FeSi powders, the influence of 400 mesh powder (fine...     

Magnetic properties of sputtered soft magnetic Fe–Ni films with an uniaxial anisotropy

The microstructure and magnetic properties of polycrystalline Fe_100−xNi_x films have been studied by X-ray diffraction (XRD) and magnetic moment measurements. In the XRD pattern of Fe–Ni films, the values of area ratio, A(1 1 1)/A(2 0 0) for the XRD peaks, in the thickness dependence decrease rapidly with increasing film thickness in the films with a bias field applied parallel to the plane in order to introduce uniaxial anisotropy, but the values for the films without the field are nearly constant. The coercivity vs. thickness analyzed by using Néel's formula show that the values for the films with the bias field follow Néel's formula within the thickness range of 40–100 nm, except the range of 10–40 nm. This result indicates that there is a change in domain wall type at the thickness of 40 nm. From the results of thickness and temperature dependence of magnetization analyzed by using some theoretical models, the values of interaction strength between magnetic ions were determined. The electrical resistivity of films is found to be consistent with the Mayadas–Shatzkes model.     

Evolution of coating layers during high-temperature annealing and their effects on magnetic behavior of Fe(Si) soft magnetic composites

Low-loss Fe(Si) soft magnetic composites (SMCs) with atomic-layer-deposition coated layer were successfully prepared in this work. The continuous, compact and uniform Al₂O₃ layer is found to form tight bonding with the powder base. Evolution of the coating layers has been investigated under different annealing temperatures and closely linked to the magnetic performance of the composites. Results indicate that 1100 °C was the optimal annealing temperature, at which the Fe(Si) SMCs showed lowest core loss of 1237 mW/cm³ and the highest permeability of 99.7 simultaneously (100 mT/100 kHz). Integrity of the coating layer ensures the maximum grain growth and stress removal of powder particles at the highest possible temperature, so as to reduce the hysteresis loss. Formation of high resistivity oxides and silicates (Al₂O₃, Fe₂SiO₄ and 3Al₂O₃·SiO₂) after annealing result in a low inter-particle eddy current loss. Besides, high temperature vacuum annealing is helpful to eliminate impurity atoms and decrease the anomalous eddy current loss. The improvement in effective permeability caused by high-temperature annealing is mainly attributed to the relaxation of residual stresses and the reduction of defects. While excessive temperature leads to the decomposition and destruction of the insulation layer, resulting in a significant increase in hysteresis loss, inter-particle and anomalous eddy current loss.     

Structure and magnetic properties of ZrO2-coated Fe powders and Fe/ZrO2 soft magnetic composites

Fe particles were coated with ZrO₂ nanopowders using mechanical milling method combined with high temperature recovery annealing process. The effect of milling time on particle size, phase structure and magnetic properties of the core-shell structure powders was studied. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) revealed that the surfaces of the composite powders comprised thin and uniform layers of ZrO₂ insulating powders after milling. Also, the SEM images showed the morphology of micro-cellular structured compacts with cell-body of Fe particles and indicated that Fe particles were well separated and insulated by thin ZrO₂ layers. The Fe/ZrO₂ soft magnetic composites displayed much higher electrical resistivity, lower core loss than that of the pure Fe powder cores without ZrO₂ layers at medium and high frequencies. The preparation method of ZrO₂-insulated Fe powders provides a promising method to reduce the core loss and improve the magnetic properties for soft magnetic composite materials.     

Magnetic barrier--A new concept in magnetic separation

Particles can be separated according to their mass magnetic susceptibilities by using a magnetic energy gradient barrier. When a stream of particles with different magnetic susceptibilities is fed to the barrier at an angle, a continuous separation can be obtained. The particles having susceptibilities higher than a predetermined value are deflected and guided by the magnetic barrier to a releasing region, where they pass through the barrier. Particles with lower susceptibilities which penetrate the barrier follow a different path from the more magnetic fraction and are separately collected.