Hopkinson Effect in Soft Magnetic Materials

1. IntroductionIt is well known that the initial permeability ofmany ferromagnetic materials increases with increasing temperature and appears a sharp peak just before the Curie point, and then drops off to a verysmall value. The peak is called the Hopkinson peakand the phenomenon is normally called the Hopkinson effectll]. Since this effect is valid for all the ferromagnetic materials, it has been used as a methodto measure the Curie temperature. However, in ourresearch work of nanocrystall…     

铁基纳米晶软磁合金的研究

本文主要评述了铁基纳米晶软磁合金的晶化过程、组织结构及其与磁性能之间的关系,分析了优异磁性能的起源,并详细论述了解释其优异磁性能的各向异性模型,提出了目前在该模型上存在的问题.此外,还介绍了纳米晶软磁材料的制备方法,并在最后对纳米晶软磁材料的应用及发展趋势作了展望.     

纳米晶软磁材料的磁性能

介绍了纳米晶软磁材料所具有的独特结构和优异的磁性能。从纳米晶软磁材料的微观组织结构和宏观磁特性紧密相关的角度,探讨了铁基纳米晶合金的结构与磁性之间的依赖关系。     

Variations of the permeability with annealing conditions for Fe-based nanocrystalline alloys

Considering the effective magnetic anisotropy of Fe-based nanocrystalline alloys contributed by the structure anisotropy and the induced anisotropy, an improved model of permeability was proposed within the framework of the random anisotropy theory. The dependence of permeability on the annealing time and temperature was analyzed, especially the peak value of permeability as a function of annealing time were explained by using this improved model. It is shown that the optimization annealing carried out at higher temperatures is more efficient and brings better soft magnetic property. The theoretical values were compared with the experimental data of a series of Fe-based nanocrystalline alloys. The results show that the theoretical analyzes are in excellent agreement with existing experiments.     

Microforging Effect on the Microstructure and Magnetic Properties of FeSiB-based Nanoflakes

The effect of microforging on the processing of nanocrystalline FeSiB alloy flakes was studied in terms of microstructure and magnetic properties. The flakes microforged from amorphous precursor showed submicron thicknesses with the crystal size of about 15 nm. The crystallite size during microforging was primarily deter- mined by plastic deformation rather than fracturing and agglomeration. Unlike the general trend of coercivity reduction with annealing, the coercivity of the nanocrystalline flakes was slightly increased with increasing an- nealing temperature, which can be explained with the diffusion anisotropy of the magnetic moments resulting from the formation of Fe-atoms pairs. The magnetic remanence (Mr) of the planar nanocrystalline flakes was measured to be about 26% of the saturation magnetization (Ms), a significant increase from 2% of the initial amorphous precursor.     

磁粉芯的研究进展

磁粉芯具有良好的软磁性能和频率特性,广泛应用于电感元件和变压器.分类介绍了纯铁粉芯、坡莫合金粉芯、铁硅铅粉芯、非晶和纳米晶粉芯的成分组成及其磁性能,重点阐述了粉末制备、绝缘包覆、压制成型和热处理等工艺参数对磁粉芯软磁性能的影响,最后指出新制备工艺的开发和相关理论模型的构建将成为未来磁粉芯研究的热点.     

The excellent soft magnetic properties and corrosion behaviour of nanocrystalline FePCCu alloys

The effects of the addition of Cu on the crystallisation behaviour, soft magnetic properties, and corrosion behaviour of Fe_84-xP₉C₇Cu_x (x = 0–1.15) alloys were investigated. The experimental results demonstrate that the glass-forming ability of this alloy was improved and the soft magnetic properties of the alloy system were enhanced by proper Cu addition. FePCCu nanocrystalline alloys with a dispersed α-Fe phase were obtained by appropriately annealing the melt-spun ribbons at 693 K for 2 min. The Fe_83.25P₉C₇Cu_0.75 nanocrystalline alloy exhibited a high saturation magnetic flux density, B _s , of 1.64 T; a low coercivity, H _c , of 3.9 A/m; and a high effective permeability, μ _e , of 21,000 at 1 kHz. These characteristics are superior to corresponding properties of FePC alloys. Furthermore, the corrosion resistance of this nanocrystalline alloy increases when elevating the annealing temperature and was confirmed to be improved with respect to the corresponding amorphous alloy. These results indicate that this alloy is a promising soft magnetic material.     

Pressure dependence of magnetoresistance for Fe/Cr multilayers

The magnetoresistance (MR) in Fe/Cr magnetic multilayers (MML) has been measured under high pressure up to 2.5 GPa. It is found that the spin-dependent scattering plays an important role in the pressure dependence of MR ratio. In the present work, for [Fe(20/spl Aring/)/Cr(10 /spl Aring/)]/sub 20/ MML with antiferromagnetic (AF) state, the pressure coefficient of saturation field H/sub s/ is (1/H/sub s/)(/spl part/H/sub s///spl part/P)=3.3/spl times/10/sup -2/ GPa/sup -1/ between 0.1 and 2.5 GPa. We found that the (1/|J|)(/spl part/|J|//spl part/P) for AF-Fe/Cr MML with polycrystalline structure is opposite in sign to that with epitaxial one. For [Fe(20 /spl Aring/)/Cr(22/spl Aring/)]/sub 20/ MML with ferromagnetic (F) state, anisotropic magnetoresistance (AMR) decreases with increasing pressure. It is suggested that the anisotropy constant decreases with weakening spin-orbit interaction at high pressure. At high field, the AMR is easily suppressed by applying pressure while the giant magnetoresistance around H/sub s/ increases slightly with increasing pressure for polycrystalline Fe/Cr MML.     

Improving the Bs and soft magnetic properties of Fe-based amorphous ribbons by manipulating the surface crystallization behavior

A novel amorphous structure coupling with ultra-fine nano α-Fe grains in the surface crystallization layer was fabricated successfully through composition regulation and proper quenching conditions. The microstructure of the newly formed surface crystallization layer and its effects on soft magnetic properties of FeMnCuMoCPSiB amorphous alloy were investigated systematically. The FeMnCuMoCPSiB amorphous alloy with surface α-Fe crystallization layers exhibits an excellent comprehensive performance of soft magnetic properties (SMPs) with high B_s of 1.67 T, low H_c of 1.6 A/m, and high μ_i of 9.3?×?10³ at 1 kHz. The SMPs of the amorphous alloy is considerably superior to that of widely used commercial soft magnetic materials METGLAS 2605, promising a potential engineering application. It is noteworthy that a nanoscale surface precipitation was found in the alloy, which favors SMPs of the alloy.

     

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.     

放电等离子烧结制备块体非晶合金研究进展

非晶合金又称“金属玻璃”,是由于超快速冷却凝固导致无法有序排列结晶,从而得到的一种长程无序结构。这种非晶合金与存在晶界和位错的普通合金相比,具有更加优异的力学及物化性能。由于粉末状或条状非晶合金在尺寸和性能等方面的限制,因而大尺寸、优异力学性能及软磁性能卓越的块体非晶合金的制备受到了大量关注与探究。放电等离子烧结技术以温度低、效率高、时间短及冷却速率快等优点,被认为是一种具有广阔发展前景的制备方法。对Fe基、Zr基、Al基及Ti基本身的特点,以及通过放电等离子烧结技术制备不同体系块体非晶合金的物理及化学性能的研究进行了较为全面的综述。概述了放电等离子烧结技术的原理及在制备块体非晶合金方面的优势;分析了放电等离子烧结技术和制备的块体非晶合金材料存在的问题,以及采用该技术制备块体非晶合金的发展前景。重点介绍了在采用该制备不同体系的块体非晶合金时,如何通过改变放电等离子烧结参数,或通过再加工、本身粉末添加元素等方法获得大尺寸、优异性能的块体非晶合金。     

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。     

Si含量对纳米晶Fe_(87-x)Cu_1Nb_3Si_xB_9合金磁性能的影响

研究了Si含量对Fe87-xCu1Nb3SixB9合金经不同方式退火后磁性能的影响。结果表明:随Si含量的增加,Fe87-xCu1Nb3SixB9合金经普通退火后软磁性能逐渐得到优化;经磁退火后可感生出单轴磁各向异性,且磁退火特征随Si含量的增加而逐渐明显。根据横磁退火实验结果计算出的感生磁各向异性值Ku,则由26.7J/m3(Si=9.5at%)降低至14.1J/m3(Si=13.5at%)。由实验数据的分析认为Fe87-xCu1Nb3SixB9合金在高Si含量时经普通退火或纵磁退火后呈现优异的软磁特性,归因于析出的α-Fe(Si)相晶粒具有小的磁晶各向异性K1,从而导致合金具有更低的有效磁各向异性常数K所至。     

Cobalt-Based Heusler Alloys for Spin-Injection Devices

Co₂MnGa and Co₂MnIn are ideal half-metallic materials for spin-injection in nanostructured semiconductor devices.Magneto-optical Kerr effect and electrical transport measurements demonstrate that although these alloys can be integrated with semiconductor devices, the metallic phase dominates over the intrinsic, minority spin phase of the alloy. Co₂MnGa : GaAs(001) has a weak uniaxial magnetic anisotropy with the easy axis along the [0,–1,1] in-plane direction. Co₂MnIn : GaAs(001) has no in-plane anisotropy. Metallic behavior is concomitant with ferromagnetic behavior, as the anisotropic magnetoresistance tends to zero at the same film thickness (100 Å) that the residual resistivity ratio extrapolates to 1. Co₂MnIn has an AMR of 0.5%, however, an AMR as large as 6% is observed in Co₂MnGa at 300 K. This demonstrates the potential for nanostructured devices, although the first 100 Å of alloy growth will determine the spin-injection efficiency.     

Magnetoelastic properties of an amorphous ferromagnetic alloy annealed by electric current

The magnetoelastic wave propagation velocity and the magnetic-field-induced change in the elastic modulus (ΔE effect) have been studied as functions of the magnetic field strength in thin stripes of an amorphous ferromagnetic alloy (Fe₆₄Co₂₁B₁₅) annealed by direct electric current of variable density. It is shown that such treatment is an effective method for obtaining amorphous ferromagnetic alloy ribbons with uniaxial anisotropy and high magnetoelastic characteristics.     

电脉冲快速退火Fe73.5Cu1Mo3Si13.5B9合金的组织与磁性能

采用电脉冲快速退火实现了非晶合金Ｆｅ７３．５Ｃｕ１Ｍｏ３Ｓｉ１３．５的纳米晶化。显微组织分析与磁性能测定结果表明,该合金经适当工艺的脉冲电流处理可得到较常规法晶粒密度更高、晶粒尺寸更小、软磁性能更优的纳米晶材料。基于随机无规磁各向异性模型,阐明了该合金的软磁性能与其显微结构的关系。     

电脉冲快速退火Fe_(73.5)Cu_1Mo_3Si_(13.5)B_9合金的组织与磁性能

采用电脉冲快速退火实现了非晶合金Ｆｅ７３．５Ｃｕ１Ｍｏ３Ｓｉ１３．５Ｂ９的纳米晶化。显微组织分析与磁性能测定结果表明,该合金经适当工艺的脉冲电流处理可得到较常规法晶粒密度更高、晶粒尺寸更小、软磁性能更优的纳米晶材料。基于随机无规磁各向异性模型,阐明了该合金的软磁性能与其显微结构的关系     

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.     

铁钴镍基非晶态软磁材料的研究

研究了１０钟以铁钴镍为基的非昌态软磁材料，对非晶态合金的成分，熔点，晶化温度，居里温度及一些磁性能作了分析比较、将将材料制成元件装到电子镇流器上试验，研究结果表明，铁磁元素铁钴镍的含量比例，是影响非晶态磁性的主要因素；类金属元素对软磁材料的磁性能也有一定的影响，含磷的非晶态合金的熔点，晶化温度及居里温度比含碳的较高。     

Giant magnetoresistance, microstructure, and application characteristics of amorphous CoNbZr-based pseudo-spin valves

We have fabricated pseudo-spin-valve (PSV) multilayers with amorphous CoNbZr alloy as a soft magnetic layer and a buffer layer by magnetron sputtering. We investigated the multilayers' giant magnetoresistance (GMR), microstructure,thermal annealing effects, and application characteristics. Our results show that the film microstructure, consequently the magnetostatic coupling effect and the magnetization reversal process, strongly depends on the CoNbZr thickness. We observed antiparallel magnetization alignments in the samples with a 2-4nm CoNbZr layer and a measured maximum GMR ratio of 6.5%. The PSV with 4 nm CoNbZr has a superior thermal stability to 400 /spl deg/C as a result of the dense and homogeneous Cu spacer. After patterning with a 6 /spl mu/m/spl times/1 /spl mu/m elliptic stripe, the structure forms a single domain. The dynamic GMR behavior under a 10 kHz sinusoidal magnetic field indicates the patterned stripe has a linear and stable GMR response. We therefore believe that PSVs with amorphous CoNbZr have good potential for spintronic devices.