高性能软磁合金的研究进展EI北大核心CSCD

软磁材料是一种极为重要且应用十分广泛的能源材料,近年来,随着磁性元件的日益高频化和小型化,以及节能环保的号召,开发和研究高性能软磁材料具有重要意义。本工作概述了软磁合金的发展历史,重点归纳出各类软磁合金(包括传统软磁合金、非晶/纳米晶软磁合金、高熵软磁合金)的成分、微观组织、磁性能以及应用范围,并总结出不同软磁合金的优、缺点;指出典型合金的微观组织对合金软磁性能(尤其矫顽力)具有关键性的主导作用,进而探讨了影响软磁合金矫顽力的因素及其微观机制,发现控制晶粒尺寸(或纳米粒子尺寸)是获得低矫顽力的关键,并描述了矫顽力的微观影响机制在高熵软磁合金中的发展;最后,展望了高熵软磁合金因多主元混合的成分特性带来的组织多样化,更有利于实现对合金性能的调控,并有望作为新一代高温软磁体材料。     

纳米硬磁晶粒间的交换耦合相互作用和有效各向异性

以纳米Nd2Fe14B永磁材料为例,研究了硬磁晶粒间交换耦合相互作用对磁体有效各向异性的影响。结果表明晶粒间交换耦合相互作用随晶粒尺寸的减小而增强,材料的有效各向异性常数Keff随晶粒尺寸的减小而逐渐下降,Keff随晶粒尺寸的变化与矫顽力的变化规律相似。纳米单相永磁材料有效各向异性的减小是矫顽力降低的主要原因,交换耦合系数口aex实际上是各向异性的减小量。为保证纳米Nd2Fe14B材料具有较高的各向异性和矫顽力,晶粒尺寸应不小于30nm。     

Structural,electrical, and magnetic properties of R-Fe-Ge (R = Y,La, Sc) films

The structural, electrical, and magnetic properties of thin R-Fe-Ge (R = Y, La, Sc) films have been studied in relation to preparation conditions (annealing temperature and the action of an external electric field on molecular vapor), film thickness, and the size of the crystallites formed in the amorphous matrix. The resistivity and coercivity of the films have been measured at temperatures from 77 to 500 K,. The results are of practical interest because the films are potentially attractive as soft-magnetic nanocrystalline materials.     

Nanocrystalline materials for high temperature soft magnetic applications: A current prospectus

Conventional physical metallurgy approaches to improve soft ferromagnetic properties involve tailoring chemistry and optimizing microstructure. Alloy design involves consideration of induction and Curie temperatures. Significant in the tailoring of microstructure is the recognition that the coercivity, (H _c) is roughly inversely proportional to the grain size (D _g) for grain sizes exceeding ∼0·1−1 μm (where the grain size exceeds the Bloch wall thickness,δ). In such cases grain boundaries act as impediments to domain wall motion, and thus fine-grained materials are usually harder than large-grained materials. Significant recent development in the understanding of magnetic coercivity mechanisms have led to the realization that for very small grain sizesD _g<∼100 nm,H _c decreases sharply with decreasing grain size. This can be rationalized by the extension of random anisotropy models that were first suggested to explain the magnetic softness of transition-metal-based amorphous alloys. This important concept suggests that nanocrystalline and amorphous alloys have significant potential as soft magnetic materials. In this paper we have discussed routes to produce interesting nanocrystalline magnets. These include plasma (arc) production followed by compaction and primary crystallization of metallic glasses. A new class of nanocrystalline magnetic materials, HITPERM, having high permeabilities at high temperatures have also been discussed.     

High coercivity in nanostructured Co-ferrite thin films

Three methods including sol-gel, rf sputtering and pulsed laser deposition (PLD) have been used for the fabrication of high coercivity Co-ferrite thin films with a nanocrystalline structure. The PLD method is demonstrated to be a possible tool to achieve Co-ferrite films with high coercivity and small grain size at low deposition temperature. High coercivity, over 10 kOe, has been successfully achieved in Co-ferrite films with a thickness of ∼ 100 nm deposited using PLD with a substrate temperature at 550°C. The Co-ferrite films prepared by PLD at over 300°C on different substrates including amorphous glass, quartz and silicon exhibits an obvious (111) textured structure and possesses perpendicular anisotropy. Our study has also shown that the high coercivity is related with a large residual strain, which may induce an additional magnetic anisotropy (stress anisotropy) and at the same time serve as pinning centres, which can restrict the domain wall movement and therefore, increase the coercivity.     

Structural and Mössbauer effect investigations of amorphous FeCuNbSiB alloys nanocrystallized (VITROPERM) in magnetic field

Melt-spun amorphous ribbons of nominal composition Fe73Cu1Nb3Si16B7, annealed at 560-580 degrees C for 1 hour in a magnetic field (H) applied along the width in the ribbon plane, develop uniaxial magnetic anisotropy with easy axis along H and exhibit several novel attributes. The samples labelled as S20 and S150 are nanocomposites consisting of ferromagnetic nanocrystalline grains (volume fraction approximately equal to 84% and 81%) of mean size d = 13(2) nm embedded in a ferromagnetic amorphous matrix and possess a magnetic permeability as large as 20,000 and 150,000, respectively. While nearly 55% of the nanocrystalline grains have a cubic DO3 Fe3Si-like structure with actual Si concentration of about 22 at.%, the remaining 45% nanocrystalline grains have tetragonal Fe3B and hexagonal Fe2Si structure. Since the crystalline volume fraction of Fe3B and Fe2Si nanocrystals is more in the sample S20, this sample exhibits stronger local magnetic anisotropy and hence lower permeability.     

Structural evolution and magnetic properties of mechanically alloyed metastable Fe–Ni–Zr–B system

Present investigation focuses on synthesizing metastable Fe₅₂Ni₂₆B₁₈Zr₄ (at.%) soft magnetic material through mechanical alloying. Mechanical alloying was employed to achieve nanocrystalline phase under optimized milling parameters such as milling speed, milling time, composition, etc. The effects of milling time on structural evolution and magnetic properties of Fe₅₂Ni₂₆B₁₈Zr₄ powders were analyzed using x-ray diffraction (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). Nano crystallization was achieved during the early stages of milling. The crystallite size of Fe₅₂Ni₂₆B₁₈Zr₄ was decreased with increasing milling time. The minimum grain size was found to be about 6 nm. The appreciable magnetic softening, in terms of coercivity values, observed as the milling progresses in amorphous phase at 25 h milling.     

Using GA–ANN algorithm to optimize soft magnetic properties of nanocrystalline mechanically alloyed Fe–Si powders

In this investigation a theoretical model based on artificial neural network (ANN) and genetic algorithm (GA) has been developed to optimize the magnetic softness in nanocrystalline Fe–Si powders prepared by mechanical alloying (MA). The ANN model was used to correlate the milling time, chemical composition, milling speed, and ball to powders ratio (BPR) to coercivity and crystallite size of nanocrystalline Fe–Si powders. The GA–ANN combined algorithm was incorporated to find the optimal conditions for achieving the minimum coercivity. By comparing the predicted values with the experimental data it is demonstrated that the combined GA–ANN algorithm is a useful, efficient and strong method to find the optimal milling conditions and chemical composition for producing nanocrystalline Fe–Si powders with minimum coercivity.     

Dual magnetic phases in Nd-based bulk metallic glass

Numerous nanocrystals dispersed homogenously in an amorphous matrix were observed in the die-cast cylindrical Nd₅₅Fe₂₈Al₉Ni₈ bulk metallic glass. Most of the nanocrystals are less than 5 nm in size. At room temperature, only one magnetically hard phase was observed. But below room temperature, another magnetically hard phase was also detected. The appearance of the phases was associated with the different exchange coupling effect of the nanocrystalline grains and the amorphous matrix, and the coercivity of the alloy was related to the size of the nanocrystals. It was shown that nanocrytals with a size larger than 1.3 nm might contribute to a larger coercivity of the alloy.     

Effect of the current annealing (without and with tensile stress) on the soft magnetic behaviour of Fe73.5-x(Co0.5Ni0.5)xSi13.5B9Nb3Cu1 alloy ribbons (x = 2.5, 5 and 10)

Experimental data on microstructural (crystalline volume fraction, grain size) and magnetic (coercive field) properties in amorphous and nanocrystalline Fe73.5-x(Co0.5Ni0.5)xSi13.5B9Nb3Cu1 alloy ribbons (x = 2.5, 5 and 10) are presented. Nanocrystalline structure was developed by annealing the precursor amorphous ribbons by current annealing (CA) and stress-current-annealing (SA). Microstructural analysis of the treated ribbons using X-ray Diffraction showed a high content of amorphous phase in the bulk. In addition, substantial changes in the crystalline state such as grain size of the samples annealed at different conditions were observed. The alloy composition also affects greatly the grain size,: increasing the (Co,Ni) content leads to higher values of the average grain size. The evolutions of the coercive field with the two kinds of thermal treatment were analysed, allowing us to conclude that the addition of (Co,Ni) tends to reduce the magnetic softness character of the original material, while the treated SA samples show higher coercivities higher than those treated without by CA.     

Phase Stability in Nanostructures

Nanostructured materials provide access to tailor‐made materials properties by microstructural design. Excellent mechanical properties such as high strength or wear resistance are often found in nanocrystalline materials. For magnetic materials, the design of nanostructured composites offers advantages if the structural scales match the intrinsic magnetic length scales. In some cases, as in the new nanocrystalline soft magnetic alloys, the combination of amorphous and nanocrystalline phases is necessary to obtain the desired properties. This rises the question of the limiting size for a stable crystalline structure, especially in contact with an amorphous phase. These considerations, which have been of interest for basic research in the context of the microcrystalline model for amorphous materials, are of technical importance for the optimization of nanostructured composites. Recent model experiments about the stability of thin Fe‐based glass forming alloy films are reviewed. A relationship between phase stability, composition, and interface density has been established. The implications of the results for the design of nanostructured alloy systems are discussed.     

Structure and magnetic properties of nanocrystalline mechanically alloyed Fe–10% Ni and Fe–20% Ni

The mechanical alloying technique has been used to prepare nanocrystalline Fe–10 and Fe–20 wt.% Ni alloys from powder mixtures. The structure and magnetic properties were studied by using X-ray diffraction and hysteresis measurements, respectively. For both alloys studied, a disordered body centered cubic solid solution forms after 24 h milling time. The higher the milling time, the larger the lattice parameter. The steady-state grain size is ≈10 nm. The reduction of the grain size increases the saturation magnetization and decreases the coercivity. Nanocrystalline Fe–10 and Fe–20 wt.% Ni have been shown to exhibit a soft magnetic behavior.     

Microstructure and magnetic properties of nano-sized Ba-Al ferrite particles by high energy ball milling

The magnetic nano-structured Ba-Al ferrite powders were prepared by high energy ball milling under the conditions of various rotation rates and milling times. The micro structure was characterized by SEM, XRD and TEM, and the magnetic properties were obtained by VSM. As the rotation rate and milling time increased, the size of nano-sized particles gradually decreased. The high energy ball milling for 5 h without relation to the rotation rate drastically reduced the coercivity as a consequence of the formation of nano-sized particle with the amorphous structure. However, the coercivity gradually decreased with increasing the milling time, resulting from the decrease of particle size with maintaining the crystal structure.     

Properties,Benefits, and Application of Nanocrystalline Structures in Magnetic Materials

The magnetic properties of nanocrystalline hard magnetic and soft magnetic are summarized. When the grain size becomes of the order f the magnetic exchange length exchange coupling occurs. The different concepts of exchange coupling in these materials are discussed. Exchange coupling leads in isotropic hard magnetic materials to a remanence enhancement. Soft magnetic materials exhibit due to exchange coupling a lower coercivity, lower losses and consequently also improved properties.     

Anisotropic Magnetoresistance Effect in Amorphous and Nanocrystalline Fe(Cu,Nb)-Si-B Alloys

1. IntroductionRecent works on the properties of Fe-basednanocrystalline alloys have generated considerable interest in the filed of materials because of their excellent soft magnetic characteristi.s[1'21. As a newlydeveloped material, the origin of the excellent softmagnetic characteristics was not clear yet. H..z.r[3]et al. have suggested that smaller magnetic crystallineanisotropy is one of the most important factors whichdominate the excellent soft magnetic characteristics,but the explanat…     

Bulk Nanocrystalline SmCo6.6Nb0.4 Sintered Magnet With TbCu7-Type Structure Prepared by Spark Plasma Sintering

We prepared bulk nanocrystalline SmCo_6.6Nb_0.4 sintered magnet material by spark plasma sintering technique. X-ray diffraction patterns show that the magnet exhibits a stable TbCu₇ structure. Transmission electron microscopy indicates that the microstructure of the magnet is composed of SmCo_6.6Nb_0.4 single-phase grains with an average grain size of 30 nm. Magnetic measurement shows that under a 7 T magnetic field, the coercivity of the magnet reaches as high as 2.8 T; the saturation magnetization and the remanence are 69.6 and 51.4 emu/g, respectively. The magnet exhibits good thermal stability with the coercivity of 0.48 T at 773 K, and the coercivity temperature coefficient beta of -0.169%/K.     

Crystallization of cobalt amorphous alloys under field annealing

Crystallization of Co-rich amorphous ribbons annealed under a 10 Oe external magnetic field at the early 30 minutes from their glassy status to supercooled liquid status is investigated by high-resolution transmission microscope (HR-TEM), Selected Area Fourier Transform (SA-FT), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results indicate that the short-rang ordering feature can be refined very well in specimen annealed under temperatures about 87.4 degrees C below their glass transition (Tg), showing refined salt-pepper morphologies with a mean length changing from 1.2 +/- 0.8 nm to 0.8 +/- 0.2 nm and a mean width shifting from 0.5 +/- 0.2 nm to 0.3 +/- 0.1 nm. When the amorphous ribbons are field-annealed at temperature near to Tg (i.e., 450 degrees C), ultra-fine nanocrystalline structures can be formed on the top surface of ribbons with size of 3.5 +/- 0.5 nm and inter-grain spacing of about 0.4 +/- 0.2 nm even though the inner parts of the ribbons are still in amorphous phases. The nanocrystalline areas are featured by the formation of doped hcp cobalt phase orientated along the c-axis, with the inter-plane spacing ranging from 4 A to 6 A. When the annealing temperature is above Tg, the grain sizes are increased dramatically with multi-phased nanocrystals precipitating from the amorphous substrate, and finally reaching almost complete crystallization at 600 degrees C, causing greatly coarsening of the nanocrystal structures.     

The effect of annealing on single-layer CoCrPtNb thin films

The effect of Nb addition on grain size segregation and intergranular coupling of ternary CoCrPt alloys prepared by annealing of crystalline samples and crystallization of the Nb-rich (more than 4.6 at.%) amorphous films is investigated. Mean surface roughness as a function of Nb addition decreased for Nb contents of up to 2.7 at.% and then increased. The size and distribution of magnetic clusters were significantly affected by Nb addition. Vacuum annealing of the ternary and quaternary films (2.7 at.% Nb) increased the coercivity of the films from 53.71 kA/m and 52.09 kA/m to about 61.14 kA/m and 105 kA/m, respectively. Film with 12.1 at.% Nb was also produced and then annealed at different times and temperatures. Increasing the temperature to 700 °C caused the recrystallization of the 12.1 at.% Nb amorphous film. The observed magnetic properties are discussed in terms of composition, crystallographic orientation of deposited layer and oxidation of elements during annealing.     

Annealing effect on the magnetic properties of Fe-Co-Zr alloy flakes

The Fe-Co-Zr alloy flakes were prepared from gas atomized powders and then annealed at various temperatures under vacuum. The products were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Furthermore, their magnetic properties, saturation flux density and coercivity, as well as the real (μ′) and imaginary (μ″) parts of complex permeability within 2-12.4 GHz were measured. The results indicate that the average grain size increase while the internal strain decreases with the increase of annealing temperature. The annealed samples show a minor decrease of saturation flux density and a significant reduction of coercivity. The μ′ of annealed sample shows larger values in comparison with the as-milled one, meanwhile, the maximum μ″ increases with the increasing temperature. The present study demonstrates that a proper annealing temperature is helpful to improve the microwave properties of metallic flakes.     

Dependence of Structure and Magnetic Properties on Annealing Temperature in Fe72.5Cu1Nb2V2Si13.5B9 Alloy

The magnetic properties of Fe72.5 Cu1Nb2V2Si13.5B9 alloy are investigated from an amorphous to a nanocrystalline and complete crystalline state.The sample annealed at 550℃ for 0.5h shows a homogeneous nanocrystalline structure and presents excellent soft magnetic properties.When the specimens were annealed at a temperature above 600℃,the magnetic properties are obviously deteriorated because the grain size grows up,exceeding the exchange length.