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High entropy alloy nanopowders were successfully prepared by liquid-phase reduction methods and their applications were preliminarily discussed. The prepared high entropy alloy nanopowders consisted of FeNi alloy spherical powders and NiFeCoCrY alloy spherical powders with a particle size of about 100 nm. The powders have soft magnetic properties, the saturation magnetization field strength were up to 5000 Qe and the saturation magnetization strength Ms was about 17.3 emu/g. The powders have the excellent property of low high-frequency loss in the frequency range of 0.3-8.5 GHz. When the thickness of the powders coating was 5 mm, the powders showed excellent absorption performance in the Ku band; and when the thickness of the powders coating was 10 mm; the powders showed good wave-absorbing performance in the X band. The powders have good moulding, and the powders have large specific surface area, so that the magnetic powder core composites could be prepared under low pressure and without coating insulators, and the magnetic powder cores showed excellent frequency-constant magnetization and magnetic field-constant magnetization characteristics. In the frequency range of 1~100 KHz; the µm of the magnetic powder core heat-treated at 800 °C reached 359, the µe was about 4.6 and the change rate of µe with frequency was less than 1%, meanwhile; the magnetic powder core still maintains constant µe value under the action of the external magnetic field from 0 to 12,000 A/m. The high entropy alloy nanopowders have a broad application prospect in soft magnetic composites.
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High-performance soft magnetic materials are important for energy conservation and emission reduction. One challenge is achieving a combination of reliable temperature stability, high resistivity, high Curie temperature, and high saturation magnetization in a single material, which often comes at the expense of intrinsic coercivity-a typical trade-off in the family of soft magnetic materials with homogeneous microstructures. Herein, a nanostructured FeCoNiSiAl complex concentrated alloy is developed through a hierarchical structure strategy. This alloy exhibits superior soft magnetic properties up to 897 K, maintaining an ultra-low intrinsic coercivity (13.6 A m-1 at 297 K) over a wide temperature range, a high resistivity (138.08 µΩ cm-1 at 297 K) and the saturation magnetization with only a 16.7% attenuation at 897 K. These unusual property combinations are attributed to the dual-magnetic-state nature with exchange softening due to continuous crystal ordering fluctuations at the atomic scale. By deliberately controlling the microstructure, the comprehensive performance of the alloy can be tuned and controlled. The research provides valuable guidance for the development of soft magnetic materials for high-temperature applications and expands the potential applications of related functional materials in the field of sustainable energy.
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It is well known that the annealing process plays a key role in tuning the properties of Fe-based amorphous soft magnetic alloys. However, the optimal annealing process for a particular amorphous alloy is often difficult to determine. Here, Fe81.4B13.2C2.8Si1.8P0.8 and Fe82.2B12.4C2.8Si1.8P0.8 amorphous alloys (denoted as Fe81.4 and Fe82.2) were prepared to systematically study the effects of the annealing temperature and time on the soft magnetic properties. The results show that the optimum annealing temperature ranges of the Fe81.4 and Fe82.2 amorphous alloys were 623 K to 653 K and 593 K to 623 K, and their coercivity (Hc) values were only 2.0-2.5 A/m and 1.3-2.7 A/m, respectively. Furthermore, a characteristic temperature Tai was obtained to guide the choosing of the annealing temperature at which the dBs/dT begins to decrease rapidly. Based on the theory of spontaneous magnetization, the relationship between Tai and the optimum annealing temperature ranges was analyzed. When the annealing temperature was higher than Tai, the effect of the internal magnetic field generated by spontaneous magnetization on the relaxation behavior was significantly reduced, and the alloys exhibited excellent soft magnetic properties. It is worth indicating that when annealed at 603 K (slightly higher than Tai), the Fe82.2 amorphous alloys exhibited excellent and stable soft magnetic properties even if annealed for a long time. The Hc of Fe82.2B12.4C2.8Si1.8P0.8 amorphous alloys was only 1.9 A/m when annealed at 603 K for 330 min. This value of Tai is expected to provide a suggestion for the proper annealing temperature of other amorphous soft magnetic alloys.
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In this work, the electromagnetic properties of Ni0.22Cu0.31Zn0.47Fe2O4 (NiCuZn) ferrites doped with 0.3 wt% Bi2O3 + xCuO flux (x = 0.2, 0.4, 0.6, and 0.8 wt%) were studied. Doping resulted in a reduction in the sintering temperature to 900 °C. The doped ferrites were synthesized via the solid-state method. XRD patterns revealed that the prepared ferrites had a cubic spinel structure; thus, a moderate addition of flux did not change the crystal structure. The SEM images, as well as the density and grain size distribution of the samples, showed that the NiCuZn ferrites had densified, homogenized, and contained fully grown grains for x = 0.6 wt%. The sample exhibited good soft magnetic properties, with µ' reaching the maximum value of 245.4 for x = 0.6 wt% and ε', Ms, and Hc reaching the maximum values of 23.1, 28.06 emu/g, and 45.86 Oe for x = 0.8 wt%, respectively. Furthermore, the ferrites exhibited good gyromagnetic properties, with 4πMs reaching the maximum value of 1744 Gauss for x = 0.8 wt% and ΔH reaching the minimum value of 228 Oe for x = 0.6 wt%. NiCuZn ferrites were successfully sintered at a lower temperature (900 °C) by adding Bi2O3-CuO flux through LTCC technology and exhibited good soft magnetic properties and gyromagnetic properties. We envisage that these ferrites could be used in multilayer devices.
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FeSiAl is a commonly used soft magnetic material because of its high resistivity, low core loss, and low cost. In order to systematically study the effect of epoxy resin (EP) on the insulated coating and pressing effect of FeSiAl magnetic powders, six groups of composite powders and their corresponding soft magnetic powder cores (SMPCs) were prepared by changing the content of EP, and the soft magnetic properties of the powders and SMPCs were characterized. The results showed that FeSiAl powders exhibited good sphericity and morphology. The Ms of FeSiAl/EP composite powders was between 117.4-124.8 emu·g-1 after adding (0.3, 0.5, 0.7, 1, 1.5, and 2 wt. %) EP. The permeability µe of SMPCs increased first and then decreased with the increase in EP content. Among them, when the EP content was 1 wt. %, the corresponding SMPCs had the highest µe and excellent DC bias performance (63%, 100 Oe). In the whole test frequency range (50~1000 kHz), SMPCs with 1 wt. % EP content had the lowest core loss (1733.9 mW·cm-3 at 20 mT and 1000 kHz). After that, the loss separation study in the low-frequency range (50~250 kHz) was conducted, and the hysteresis loss and eddy current loss of SMPCs with 1 wt. % EP content were also the lowest. In addition, SMPCs also exhibited the best overall performance when the EP content was 1 wt. %. The results of this study can guide the design of composite insulation coating schemes and promote the development of soft magnetic materials for medium and high frequency applications.
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The effect of laser irradiation and tensile stress on the microstructure and soft magnetic properties of the FeSiBNbCu nanocrystalline alloy prepared using a continuous laser has been investigated. The experimental results indicate that a decreased laser scanning speed provides more thermal energy to induce nanocrystals and encourage grain growth. When the scanning speed is excessively high, the crystallization process will cease due to a lack of energy to drive diffusion phase transitions. Nevertheless, the introduction of tensile stress could significantly promote crystallization in FeSiBNbCu alloy samples irradiated at these high laser scanning speeds. This phenomenon can be attributed to the augmentation of compressive thermal stress at the interface between the laser-treated track and the untreated region. This heightened compressive stress promotes the diffusivity of atoms, and, as a result, the transformation from amorphous to crystalline states can be enhanced. As the applied tensile stress increases, both grain size and crystalline volume fraction exhibit a proportional augmentation. Consequently, these changes manifest in the soft magnetic properties. The crystalline volume fraction can reach 62%, and the coercivity is 2.9 A/m at the optimized scanning speed; these values correspond to 54% and 3.3 A/m under specific tensile stress loading.
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Droplet manipulation has garnered significant attention in various fields due to its wide range of applications. Among many different methods, magnetic actuation has emerged as a promising approach for remote and instantaneous droplet manipulation. In this study, we present the bidirectional droplet manipulation on a magnetically actuated superhydrophobic ratchet surface. The surface consists of silicon strips anchored on elastomer ridges with superhydrophobic black silicon structures on the top side and magnetic layers on the bottom side. The soft magnetic properties of the strips enable their bidirectional tilting to form a ratchet surface and thus bidirectional droplet manipulation upon varying external magnetic field location and strength. Computational multiphysics models were developed to predict the tilting of the strips, demonstrating the concept of bidirectional tilting along with a tilting angle hysteresis theory. Experimental results confirmed the soft magnetic hysteresis and consequential bidirectional tilting of the strips. The superhydrophobic ratchet surface formed by the tilting strips induced the bidirectional self-propulsion of dispensed droplets through the Laplace pressure gradient, and the horizontal acceleration of the droplets was found to be positively correlated with the tilting angle of the strips. Additionally, a finite element analysis was conducted to identify the critical conditions for dispensed droplet penetration through the gaps between the strips, which hinder the droplet's self-propulsion. The models and findings here provide substantial insights into the design and optimization of magnetically actuated superhydrophobic ratchet surfaces to manipulate droplets in the context of digital microfluidic applications.
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In this experiment, the rare earth Gd element was added to Finemet alloy to observe the microstructure and soft magnetic properties. The experimental results showed that the samples with the addition of 0.5% Gd and 1.0% Gd can be quenched and cast normally, and the MS of Fe73Cu1Nb3Si13.5B9Gd0.5 alloy was 10.41% higher than that of Finemet. After annealing, crystal grains of about 10 nm were formed. The µi and µm values of Fe73Cu1Nb3Si13.5B9Gd0.5 alloy were 25.51% and 22.23% higher, respectively, and the coercivity HC was reduced by 12.19% compared to Finemet. At 1 kHz, the µe value of Fe73Cu1Nb3Si13.5B9Gd0.5 alloy at room temperature was 14.57% higher than that of Finemet, while the µe reached 162.34 k and 142.42 k at 90 °C and 150 °C (24% and 29.51% higher, respectively). The Fe72.5Cu1Nb3Si13.5B9Gd1.0 alloy had the best performance at 100 kHz, with higher µe values than Finemet across the ambient temperature range of 30 °C to 150 °C. After tension annealing, the µe values of Fe72.5Cu1Nb3Si13.5B9Gd1.0 alloy were 20-30% higher than those of Finemet.
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In order to decrease and control electromagnetic pollution, absorbing materials with better electromagnetic wave absorption properties should be developed. In this paper, a nanocrystalline alloy ribbon with the composition of Fe73.2Si16.2B6.6Nb3Cu1 was designed and prepared. Nanocrystalline alloy powder was obtained by high-energy ball milling treatment. The effects of ball milling time on the soft magnetic properties, microstructure, morphology, and electromagnetic wave absorption properties of alloy powder were investigated. The results showed that, as time increased, α-(Fe, Si) gradually transformed into the amorphous phase, and the maximum saturation magnetization (Ms) reached 135.25 emu/g. The nanocrystalline alloy powder was flakelike, and the minimum average particle size of the powder reached 6.87 µm. The alloy powder obtained by ball milling for 12 h had the best electromagnetic absorption performance, and the minimum reflection loss RLmin at the frequency of 6.52 GHz reached −46.15 dB (matched thickness was 3.5 mm). As time increased, the best matched frequency moved to the high-frequency direction, and the best matched thickness decreased, while the maximum effective absorption bandwidth ΔfRL<−10 dB was 7.22 GHz (10.78−18 GHz).
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Multiprincipal-element alloys (MPEAs), including high-entropy alloys, are a new class of materials whose thermodynamical properties are mainly driven by configuration entropy, rather than enthalpy in the traditional alloys, especially at high temperatures. Herein, the design of a novel soft-magnetic nonequiatomic, quaternary MPEA is described, via tuning its chemical composition to deliberately manipulate its microstructure, such that it contains ultrafine ferromagnetic body-centered-cubic (BCC) coherent nanoprecipitates (3-7 nm) uniformly distributed in a B2-phase matrix. The new alloy Al1.5 Co4 Fe2 Cr exhibits high saturation magnetization (MS = 135.3 emu g-1 ), low coercivity (HC = 127.3 A m-1 ), high Curie temperature (TC = 1061 K), and high electrical resistivity (ρ = 244 µΩ cm), promising for soft magnets. More importantly, these prominent soft-magnetic properties are observed to be retained even after the alloy is thermally exposed at 873 K for 555 h, apparently attributable to the excellent stability of the coherent microstructure. The versatility of the magnetic properties of this new alloy is discussed in light of the microstructural change induced by tuning the chemical composition, and the enhanced performance of the alloy is compared directly with that of the traditional soft-magnetic alloys. The perspective is also addressed to design high-performance soft-magnetic alloys for high-temperature applications.
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The lack of strength and damage tolerance can limit the applications of conventional soft magnetic materials (SMMs), particularly in mechanically loaded functional devices. Therefore, strengthening and toughening of SMMs is critically important. However, conventional strengthening concepts usually significantly deteriorate soft magnetic properties, due to Bloch wall interactions with the defects used for hardening. Here a novel concept to overcome this dilemma is proposed, by developing bulk SMMs with excellent mechanical and attractive soft magnetic properties through coherent and ordered nanoprecipitates (<15 nm) dispersed homogeneously within a face-centered cubic matrix of a non-equiatomic CoFeNiTaAl high-entropy alloy (HEA). Compared to the alloy in precipitate-free state, the alloy variant with a large volume fraction (>42%) of nanoprecipitates achieves significantly enhanced strength (≈1526 MPa) at good ductility (≈15%), while the coercivity is only marginally increased (<10.7 Oe). The ordered nanoprecipitates and the resulting dynamic microband refinement in the matrix significantly strengthen the HEAs, while full coherency between the nanoprecipitates and the matrix leads at the same time to the desired insignificant pinning of the magnetic domain walls. The findings provide guidance for developing new high-performance materials with an excellent combination of mechanical and soft magnetic properties as needed for the electrification of transport and industry.
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Microwave radar absorbing materials have been the focus of the radar stealth research field. In this study, ceramic structured porous honeycomb-like Al2O3 film was prepared by anodic oxidation, and an Ni layer was deposited on the Al2O3 film via electrodeposition in a neutral environment to form a flower- and grain-like structure in a three-dimensional (3D) network Ni/Al2O3/Ni film. The films both have a through-hole internal structure, soft magnetic properties, and absorb microwaves. The dielectric loss values of two films were little changed, and the maximum microwave absorption values of flower- and grain-like Ni/Al2O3/Ni film were -45.3 and -31.05 dB with relatively wide effective bandwidths, respectively. The porous ceramic structure Al2O3 interlayer prevented the reunion of Ni and isolated the eddy current to improve the microwave absorption properties. The material presented in our paper has good microwave absorption performance with a thin thickness, which indicates the potential for lightweight and efficient microwave absorption applications.
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In this paper, a single phase ε-Fe(Si)3N powder was successfully synthesized through the salt bath nitriding reaction method. The flaky FeSi alloy powder was used as the iron source, and non-toxic CO(NH2)2 was used as the nitrogen source. The nitridation mechanism, the preparation technology, the soft magnetic properties, and the magnetization temperature dependence of the powder were studied. The research result showed that ε-Fe(Si)3N alloy powders were synthesized in a high temperature nitrification system after the surface of flaky FeSi alloy powders were activated by a high-energy ball mill. The optimum nitriding process was nitridation for 1 h at 550 °C. The ε-Fe(Si)3N powder had good thermal stability at less than 478.8 °C. It was shown that ε-Fe(Si)3N powder has good soft magnetic properties, and the saturation magnetization of the powder was up to 139 emu/g. The saturation magnetization of ε-Fe(Si)3N powder remains basically constant in the temperature range of 300â»400 K. In the temperature range of 400â»600 K, the saturation magnetization decreases slightly with the increase of temperature, indicating that the magnetic ε-Fe(Si)3N powder has good magnetization temperature dependence.
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High-entropy alloys (HEAs) with soft magnetic properties are one of the new candidate soft magnetic materials which are usually used under an alternating current (AC) magnetic field. In this work, the AC soft magnetic properties are investigated for FeCoNixCuAl (1.0 ≤ x ≤ 1.75) HEAs. The X-ray diffraction (XRD) and scanning electron microscope (SEM) show that the alloy consists of two phases, namely a face-centred cubic (FCC) phase and a body-centred cubic (BCC) phase. With increasing Ni content, the FCC phase content increased. Further research shows that the AC soft magnetic properties of these alloys are closely related to their phase constitution. Increasing the FCC phase content contributes to a decrease in the values of AC remanence (AC Br), AC coercivity (AC Hc) and AC total loss (Ps), while it is harmful to the AC maximum magnetic flux density (AC Bm). Ps can be divided into two parts: AC hysteresis loss (Ph) and eddy current loss (Pe). With increasing frequency f, the ratio of Ph/Ps decreases for all samples. When f ≤ 150 Hz, Ph/Ps > 70%, which means that Ph mainly contributes to Ps. When f ≥ 800 Hz, Ph/Ps < 40% (except for the x = 1.0 sample), which means that Pe mainly contributes to Ps. At the same frequency, the ratio of Ph/Ps decreases gradually with increasing FCC phase content. The values of Pe and Ph are mainly related to the electrical resistivity (ρ) and the AC Hc, respectively. This provides a direction to reduce Ps.
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Herein, we demonstrate the successful synthesis of novel Fe80Si9B(11−x)Px (x = 0, 1, 3, 5, 7) ultra-thick amorphous ribbons by planar flow casting. The influence of P alloying on glass forming ability (GFA), microstructure, thermal stability, soft magnetic properties, and ductility has been systematically investigated. The results reveal that introduction of P into Fe80Si9B11 alloy can remarkably enhance the GFA and increase critical thickness (tc) of the alloy from 45 to 89 um. Furthermore, the annealed FeSiBP amorphous alloys exhibited excellent soft magnetic properties, including high saturation magnetic flux density of 1.54 T, the low coercivity of 1.5 A/m, and low core losses of 0.15 W/kg. In addition, the representative Fe80Si9B8P3 ultra-thick amorphous alloy demonstrate excellent ductility even after annealing at 400 °C for 10 min, which indicates the superior performance of P-doped FeSiB alloys as compared to the commercial Fe78Si9B13 (Metglas 2605 S2) alloy. The combination of high GFA, excellent ductility, and low core losses of newly developed FeSiBP amorphous soft magnetic alloys makes them attractive candidates for magnetic applications in the high-frequency and high-speed electric devices.
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The soft magnetic properties of Fe-based nanocrystalline alloys are determined by their grain size. In the present article, the (Fe0.4Co0.6)79Nb3B18 nanocrystalline alloys have been successfully prepared by isothermal annealing. The variation of soft magnetic properties as a function of annealing temperature and incubation time is investigated in detail. Two distinct crystallization behaviors were found for the (Fe0.4Co0.6)79Nb3B18 alloys. The initial nanocrystallization products comprise a mixture of α-Fe(Co), Fe2B, and Fe23B6-type crystalline metastable phases, and the final crystallization products are composed of α-Fe(Co), Fe2B, and Fe3B crystalline phases. The grain size decreases first and then increases with the increasing annealing temperature in the range of 764â»1151 K, and a fine grain size with mean grain size of 12.7 nm can be achieved for alloys annealed at 880 K. As the annealing temperature increases from 764 K to 1151 K, the saturation magnetization increases first and then decreases without a significant increase of the coercivity. The alloys annealed at 880 K exhibit the optimized soft magnetic properties with high Ms of 145 emu g-1 and low Hc of 0.04 Oe.