放电等离子烧结制取的Nd-Fe-Co-V-B系交换弹簧磁体

交换弹簧磁体是由纳米尺寸的硬磁相和软磁相混合组成的复合磁体。由于软磁相与硬磁相的交换耦合而阻碍了软磁相的磁化反转 ,因而可发挥如同单一硬磁相磁体同样的效果 ,所以有可能获得磁性能很高的磁体。如果在硬磁相的结晶具有一定的取向性时 ,就有可能获得在理论上磁特性优越的Ｎｄ Ｆｅ Ｂ系烧结磁体。实际上交换弹簧磁体可望获得最高磁特性的组合 ,当前主要研究了以Ｎｄ2 Ｆｅ14 Ｂ相为硬磁相和以α Ｆｅ或Ｆｅ3Ｂ为软磁相的各相同性磁体。为了获得这种交换弹簧磁体所特有的纳米晶粒组织 ,当前最常用的方法是采取熔体急冷法首先得到非晶…     

纳米复合磁体

α—Fe是具有极高饱和磁化强度的软磁相,而Nd2Fe14B则是具有高度结晶磁各向异性的硬磁相,这两相以纳米尺寸周期性组合成一体的复合材料即称之为纳米复合磁体。这种软磁相与硬磁相通过交换耦合作用而形成具有很高饱和磁化强度和矫顽力的单一相,在理论上可得到前所未有的高磁能积。例如由软磁相Fe45Co35与硬磁相Sm2Fe13N3所组成的纳米复合磁体,     

熔体旋淬的Pr2Fe14B/α-Fe纳米复合磁体

由硬磁相和软磁相两相混合组成的纳米复合磁体具有优越的磁性能 ,很有可能成为一类重要的实用永磁体。纳米复合磁体的磁性能与其显微组织密切相关 ,其软磁相尺寸要比硬磁相畴壁宽度为了在硬磁相与软磁相之间获得最佳的交换耦合重要得多。为获得最佳性能的纳米复合磁体的最佳显微组织 ,是由平均晶粒直径约为 10ｎｍ的软磁相与平均直径约为 2 0ｎｍ的硬磁相所组成。但是为了获得理想的双相显微组织是不可能的。为了由快淬非晶合金得到α Ｆｅ细晶 ,可添加Ｎｄ和Ｚｒ之类元素作为在晶化退火时阻止α Ｆｅ晶粒长大的抑制剂 ,但这又会导致纳米磁…     

厚度减薄对Fe_(81)B_(13.5)Si_(3.5)C_2非晶薄带磁各向异性和磁矩取向分布的影响

急冷法制备的非晶软磁材料的实用磁性与其磁各向异性和磁矩取向分布密切相关。大量研究表明,急冷状态的过渡金属-类金属非晶合金薄带里的磁畴结构和磁矩取向主要取决于淬火急冷内应力。Becker通过磁化测量发现,表面层去除和厚度减薄对急冷内应力系统没有影响。Takahashi等的磁转矩研究表明,急冷态非晶薄带2个表面附近的磁各向异性最大。对急冷态非晶薄带的Moss-bauer研究表明,磁矩取向主要分布在薄带平     

Nd—Fe—B—Cr纳米晶复合磁体的磁性能

以Nd2Fe14B为基础的稀土永磁体具有大磁化强度、高居里温度和高磁各向异性．尽管进行了大量研究，但没有找到磁性超过Nd2Fe14B的新型永磁材料．目前，大量的注意力集中在有可能超过Nd2Fe14B烧结磁体的交换耦合纳米晶复合磁体，这种磁体是由纳米尺度的软磁和硬磁化合物晶粒组成的．在Nd－Fe－B系统中，t－Fop、Fop和肝Fe为软磁相，Nd2Fe14B为硬磁相．纳米品复合磁体具有由软磁相造成的大过饱和磁化强度和硬磁相产生的高桥涵磁力，因此，这种材料的进性依赖于复合相的种类和技量．同时，深加少量的元素（AISt，y，CrGa，An，蛇等）…     

纳米复相永磁材料交换耦合作用的评述

对比纳米复相永磁材料一维到三维的不同交换耦合作用模型,交换耦合作用会抑制软磁相的磁化反转,不同交换耦合作用模型对矫顽力影响不同。Henkel曲线δM峰值越高表明晶粒间交换耦合作用越强,一阶翻转曲线(first order reversal curve,FORC)峰值对应交换耦合作用强弱。纳米复相永磁材料有效各向异性K_eff随晶粒尺寸减小而下降,当晶粒尺寸一定时,软磁相体积分数越高K_eff越低。为了得到最大磁能积高并且K_eff不低的纳米复相永磁材料,软磁相晶粒尺寸应在10nm左右,软磁相体积不能超过50%。     

Nb-Fe-B系纳米晶复合磁体的磁特性

Ｎｂ－Ｆｅ－Ｂ系纳米晶复合磁体的磁特性纳米晶复合磁体是指由２０ｎｍ左右微细晶粒的软磁相与硬磁相组成的磁体。Ｎｂ－Ｆｅ－Ｂ系纳米复合磁体是软磁相ｔ－Ｆｅ３Ｂ、Ｆｅ２Ｂ、α－Ｆｅ和硬磁相Ｎｄ２Ｆｅ１４Ｂ组成，其磁特性在颇大程度上取决于软磁相和硬磁相的种类...     

不同相厚度下对SrFe12O19/α-Fe纳米复合双层膜的微磁学模拟

采用三维模拟软件OOMMF对铁氧体纳米复合双层膜SrFe₁₂O₁₉/α-Fe进行微磁学模拟研究。结果显示,固定硬磁相厚度分别为10、15和20 nm,逐渐增大软磁相厚度,复合材料均表现出剩磁增强效应,计算(BH)_max分别在软磁相厚度L_s=5 nm,6 nm和6 nm时取得最大值165.57,136.39和117.32 kJ/m³,是目前单相锶铁氧体的(BH)_max(40 kJ/m³)的3~4倍左右。在软磁相厚度相同的条件下,随着硬磁相厚度的增加,复合材料的剩磁、最大磁能积逐渐减小,矫顽力略有增大,最佳的(BH)_max在硬磁相厚度为10 nm时取得。磁矩反转过程随着硬磁相厚度的变化而表现出不同的特点。     

纳米复合永磁体

烧结Ｎｄ磁体已广泛用于电脑、核磁共振诊断装置、马达、通讯音响机器等方面,这种磁体是以主相Ｎｄ２Ｆｅ１４Ｂ的高磁晶各向异性为基的结晶组织。而新发展起来的纳米复合磁体,则是由硬磁相与软磁相所组成的微细双相组织,它利用了硬碰相的高磁晶各向异性与软磁相的高饱和磁化强度微细构造的两相交换相互作用,而发挥出高的磁特性。硬磁相常用Ｎｄ２Ｆｅ１４Ｂ而软磁相为Ｆｅ或Ｆｅ３Ｂ,作为合金成分以Ｎｄ、Ｆｅ、Ｂ为主,为提高居里点而添加微量Ｃｏ,为提高矫顽力而加入微量Ｎｂ、Ｖ和Ｍｏ等。纳米复合永磁的制造方法不同于烧结Ｎｄ磁…     

Nd-Fe-B/α-Fe系纳米复合薄膜的磁性

纳米复合磁体由纳米级混合的软磁相与硬碰相构成，由于软磁相-碰相间的交换耦合而阻止软磁相的磁化反转，如果能形成理想的复合构造将有可能获得超越Ｎｄ－Ｆｅ－Ｂ磁体磁性能的纳米复合磁体。这种磁体的磁特性对于其微结构（软磁相和硬磁的晶粒粒径，结晶取向，体积比）的依赖关系很大，通常用急冷法等工艺难以系统地控制其微结构，然而薄膜法却能够通过变化膜厚和基板温度等制备条件来控制其微结构。根据这一观点，近年来已广泛研究了Ｎｄ－Ｆｅ－Ｂ／Ｆｅ系、ＳｍＣｏ／Ｆｅ系等多层膜纳米复合磁体。在这类多层膜系中，通过改变软磁层与…     

Effects of applied stress on coherent precipitates via a discrete atom method

Morphological evolution of coherent precipitates under an applied stress is analyzed by means of a discrete atom method, which is predicated upon Hookean atomic interactions and Monte Carlo diffusion, and mates no assumption of a specific shape. Precipitates having elastic constants different from those of the matrix phase art treated in dislocation-free, anisotropic elastic systems under a plane strain condition with a purely dilatational misfit. Under an applied tensile stress, soft particles with a positive misfit strain tend to become plates perpendicular to the applied stress axis, while hard particles elongate along the stress direction. If the elastic interaction between the applied stress and the coherency strain is strong enough, precipitates often split into smaller particles and then follow coarsening. Even in the absence of a coherency strain, particles are shown to undergo morphological evolution through Eshelby’s inhomogeneity effects. A particle shape depends on the following variables: the sign and magnitude of the coherency strain, the sense and magnitude of the applied stress, its stiffness relative to the matrix phase, and the magnitude of the interfacial energy.     

软磁薄带（丝）的巨磁阻抗效应及其应用

介绍了居磁阻抗效应的来源，综述了它和样品的磁各向异性，驱动电流的频率，样品的电导率及厚度的关系，并简要介绍了它的应用。     

Micromagnetic simulation of Au interlayer in L1_0-FePt nanocomposite recording medium

Owing to the epitaxial inducement of Au atom,Au interlayer was introduced to increase the perpendicular anisotropy and the coercivity in L1_0-FePt nanocomposite film.Micromagnetics can be used to reveal the relationship between microstructure and magnetic properties of materials,and give the information of the perpendicular anisotropy and coercivity.In this work,the effect of the Au interlayer on annealed[Fe(0.5 nm)/Pt(0.5 nm)/Au(d nm)]_(10) nanocomposite recording medium by a micromagnetic model was studied.The model contains three phases:hard magnetic phase,soft magnetic phase,and nonmagnetic phase.The calculated result shows that perpendicular orientation degree of the texture and proportion of a hard magnetic phase to the total phase in the annealed film are both enhanced by increasing Au interlayer thickness.This result can be conducive to the improvement of the perpendicular anisotropy and the coercivity of the FePt nanocomposite film in the experiments.     

熔体温度对快淬法制备纳米晶复合Nd_(8.5)Fe_(77)Co_5Zr_3B_(6.5)合金微观结构和磁性能的影响

将Nd_(8.5)Fe_(77)Co_5Zr_3B_(6.5)(at%)合金熔化至不同温度后,以18 m/s的甩带速度快淬,对淬态条带进行了退火处理,分析了其微观结构和磁性能的变化。结果表明,熔体温度对淬态及其退火态合金的微观结构和磁性能可以产生重要影响,熔体温度为1210℃时制备的快淬条带由Nd_2Fe_(14)B相和部分非晶相组成,具有一定的硬磁性;随着快淬时熔体温度的升高,淬态条带中非晶相的质量分数逐渐增加,其磁性逐渐转变为软磁性。几种合金经退火处理后均由大量Nd_2Fe_(14)B相与少量软磁相组成,熔体温度较低的合金退火后其晶粒尺寸较小,磁性能较好。熔体温度为1210℃时制备的合金退火后磁性能最佳,内禀矫顽力Hci为559.2 kA/m,剩余磁化强度Br为0.98 T,最大磁能积(BH)_(max)为127.8 kJ/m~3。     

带厚对FeSiB非晶铁芯软磁性能的影响

研究了带材厚度对非晶环形铁芯软磁性能的影响,铁芯由标称成分为Fe91.7Si5.3B3.0(质量分数),分别为带厚22μm,25μm和26μm的带材制成。铁芯在氮气保护下经过653~723K保温1h进行热处理。在5~30kHz以及200~1 000mT(Bm)范围内测试铁芯软磁性能。研究表明,带材厚度影响铁芯软磁性能,随着带材厚度的减小,铁芯动态损耗值、矫顽力和剩磁都逐渐减小,带厚22μm带材绕制的铁芯可以获得最优的软磁性能。     

Electroplated Bimagnetic Microwires: From Processing to Magnetic Properties and Sensor Devices

Multilayer microwires with biphase magnetic behavior are revisited in this work. They are fabricated by the combination of ultrarapid solidification and electroplating techniques, and they are composed by ferromagnetic nucleus, intermediate glass layer, and ferromagnetic outer shell. Different magnetic configurations have been explored: soft/hard (CoFeSiB/CoNi and FeSiB/CoNi), soft/soft (CoFeSiB/FeNi), and hard/soft (FePtSi/FeNi). Their magnetic properties are mainly determined by the magnetic interactions between both magnetic phases: (I) a magnetoelastic coupling that arises from the mechanical stresses induced during the growth of the external magnetic shell and (II) a magnetostatic bias field that arises from uncompensated magnetic charges of the hard layer. Most outstanding static (i.e., low-field hysteresis loops) and dynamic (i.e., magnetoimpedance and ferromagnetic resonance) properties are reviewed in this article. The possibility to tailor the magnetization reversal of the soft phase through the tuning of those magnetic couplings places multilayer biphase microwires in a very competitive position as functional sensing elements suitable for a number of technological applications. In particular, we focus on their use in multifunctional sensor devices and fluxgate applications.     

BEHAVIOUR OF BUFFER LAYER IN JOINING OF SIALON CERAMICS TO STEEL 40Cr

The buffer layer material itself may be influential to the bond strength between active brazingfiller and ceramics.For Ag_(57)Cu_(38)Ti_5 filler metal,Cu or Ta is excellent buffer layer material,but Kovar or Ni-15Cr-15Co is worse.It was important to design a layer of soft buffer,suchas Cu,to relax interfacial stress rather than hard buffer layer,such as Mo,to avoid stress.There is an optimum thickness range of soft buffer layer,saying h/L=0.02—0.1. It was agood solution to the interfacial stress problem to use soft/hard buffer layer to increasemetal/ceramics joint strength.Finally,an idea of designing gradual materials as buffer layerbetween metal and ceramics was suggested.     

Fe44Co20Nd7Nb4B25大块非晶合金磁性及热稳定性研究

采用铜模吸铸法制备了Fe44Co20Nd7Nb4B25大块非晶合金,利用差示扫描量热仪(DSC)、X射线衍射仪(XRD)、高分辨透射电镜(HRTEM)和振动样品磁强计(VSM)研究了该合金的结构、非晶形成能力、热稳定性及磁性能.结果表明:该合金为完全非晶结构,在室温下表现为良好的软磁性,并具有较好的非晶形成能力和热稳定性,晶化激活能Ep为642 kJ/mol.退火后该合金表现为硬磁性,退火温度为1003 K时,内禀矫顽力iHc达到最大值,为l164kA/m;退火温度为963 K时,剩余磁感应强度研和最大磁能积(BH)max的值最大,分别为0.27 T和15.79 kJ/m3.     

Preparation and Magnetic Properties of Anisotropic SmCo_5/Co Composite Particles

Anisotropic SmCo_5/Co nanocomposite powders have been prepared by electroless Co deposition on commercial SmCo_5 powders with hydrazine as reducer. The Co particles are mainly in the range of 8–27 nm and form dense/continuous soft magnetic coatings on the surface of SmCo_5 powders. Exchange coupling happened between the coated Co soft magnetic particles and the SmCo_5 hard phase. As a result, SmCo_5/Co nanocomposite powders with remanence of73.58 emu/g and energy product of 13.74 MGOe were obtained in the optimum condition, as compared with those of70.52 emu/g and 13.40 MGOe for uncoated SmCo_5 powders. The effects of Co adding amount on Co particle size, coating morphology, and magnetic properties of SmCo_5/Co products were investigated.