共查询到19条相似文献,搜索用时 203 毫秒
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以软磁性相α—Re和硬磁性相Nd2Fe14B为例,研究了软—硬磁性晶粒间的交换耦合相互作用和有效各向异性随晶粒尺寸和软、硬磁性晶粒尺寸比(Ds:Dh)的关系,软—硬磁性晶粒间的有效各向异性常数可以用软、硬磁性相的平均各向异性常数的统计平均值表示,当晶粒尺寸大于其铁磁交换长度时,晶粒分为有、无交换耦合两部分,无交换耦合部分的各向异性常数为通常的K1,而耦合部分的各向异性常数随到晶粒表面的距离而变化,研究结果表明:软—硬磁性晶粒间的有效各向异性随晶粒尺寸的减小而下降,随着软、硬磁性晶粒尺寸比值(Ds:Dh)的减小而增加,为使软—硬磁性晶粒间的有效各向异性常数Keff保持较高的值,应控制硬磁性晶粒大于35nm,软磁性晶粒尺寸为10nm左右。 相似文献
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以Nd2Fe14B/α—Fe为例,研究了晶粒之间交换耦合相互作用对纳米复合永磁体有效各向异性的影响。纳米复合永磁体的有效各向异性常数可用软—软、硬—硬、软—硬三种不同晶粒界面对应有效各向异性常数的统计平均值表示。计算结果表明:材料的有效各向异性常数Keff随软磁性相成分的增加而降低;在相成分比例一定的条件下,随软、硬磁性相晶粒尺寸比值的增加而增加。 相似文献
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Nd2Fe14 B/α-Fe纳米复合永磁材料的有效各向异性 总被引:2,自引:0,他引:2
Nd2Fe14B/α-Fe纳米复合永磁材料中存在软-软、软-硬、硬-硬3种不同磁性晶粒界面。不同晶粒间的交换耦合相互作用使其有效各向异性常数Keff减小。Keff可以用这3种不同有效各向异性的统计平均值表示。计算结果显示:如随晶粒尺寸D的减小和软磁性成分的增加而降低。当D减小到4nm时,Keff减小为通常各向异性常数值的1/3∽1/4。当软磁性相体积分数为50%时,Keff的值下降为硬磁性相对应值的1/2左右。有效各二向异性与矫顽力的变化规律基本相同。 相似文献
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采用热压/热变形工艺制备纳米复合Nd9Fe84.5Co1B5.5永磁体,研究了热变形过程中的变形量对磁体平均晶粒尺寸的影响以及由此带来的晶间相互作用和矫顽力的变化。结果表明变形量54%的磁体中的硬、软磁性相的平均晶粒尺寸分别为61.0和51.8nm,与其热压状态时的两相平均晶粒尺寸(52.1和54.0nm)接近;而变形量74%的磁体中的硬、软磁性相的平均晶粒尺寸则分别显著减小至19.2和22.4nm。随着两相晶粒尺寸的显著细化,磁体中的晶间相互作用由以静磁耦合作用为主转变为以晶间交换耦合作用为主,这导致其矫顽力提高了64%。 相似文献
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用真空快淬法制备Nd12Fe84B6非晶态薄带,经700℃真空退火处理,获得Nd2Fe14B/α-Fe双相纳米晶复合永磁材料.用中子衍射的方法对两种不同退火时间的样品进行室温相结构分析,并根据尺寸效应引起的衍射线展宽得到了晶粒的平均尺寸.研究结果表明:对退火时间为20min和90min的样品, Nd2Fe14B硬磁性相的平均晶粒大小分别为52.1nm和55.3nm,α-Fe软磁性相的平均晶粒大小分别为61.5nm和66.2nm;软、硬磁性相的晶粒大小几乎没有变化.随着退火时间的增加,Nd2Fe14B硬磁性相的体积分数增加,而α-Fe软磁性相的体积分数则减少.磁性测量及剩磁分析表明:90min的样品磁性能优于20min的样品,90min样品软、硬磁性相晶粒之间的交换耦合作用>20min的样品. 相似文献
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Nd3Fe14B/α—Fe纳米晶复合永磁材料的中子衍射结构分析及磁性研究 总被引:1,自引:1,他引:0
用真空快淬法制备Nd12Fe84B6非晶态薄带,经700℃真空退火处理,获得Nd2Fe14B/α-Fe双相纳米晶复合永磁材料.用中子衍射的方法对两种不同退火时间的样品进行室温相结构分析,并根据尺寸效应引起的衍射线展宽得到了晶粒的平均尺寸.研究结果表明:对退火时间为20min和90min的样品, Nd2Fe14B硬磁性相的平均晶粒大小分别为52.1nm和55.3nm,α-Fe软磁性相的平均晶粒大小分别为61.5nm和66.2nm;软、硬磁性相的晶粒大小几乎没有变化.随着退火时间的增加,Nd2Fe14B硬磁性相的体积分数增加,而α-Fe软磁性相的体积分数则减少.磁性测量及剩磁分析表明:90min的样品磁性能优于20min的样品,90min样品软、硬磁性相晶粒之间的交换耦合作用>20min的样品. 相似文献
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《功能材料》2016,(2)
纳米复合磁体的磁能积能得到大幅度提高,前提是晶粒之间存在良好的交换耦合作用,而交换耦合作用与软、硬磁相之间的界面密切相关。对Nd_2Fe_(14)B、Sm-Co、FePt基纳米复合磁体界面交换耦合和反磁化的研究展开论述。在不同的条件下,界面结构的匹配性、界面原子扩散、晶间的非晶相、界面非磁性层、界面晶格弛豫等可能有利于改善界面的结构、增强交换耦合作用,进而对反磁化过程产生影响。反磁化的不可逆过程主要发生在硬磁相内,但与软、硬磁相界面特性密切相关。不可逆反磁化在一定程度上决定了磁体的矫顽力,它可通过改善界面结构进行调控。本文旨在对纳米复合磁体界面的作用深入理解并期望能对磁体磁性能的优化提供参考。 相似文献
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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. 相似文献
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Structure and magnetic properties of the nanocomposite magnets prepared by mechanical alloying procedure with composition 55 wt pct Nd (Fe0.92B0.08)5.5+45 wt pct a-Fe, 55 wt pct Nd(Fe0.8-xCo0.12Nbx B0.08)5.5+45 wt pct a-Fe (x=0.00, 0.01, 0.03) and 55 wt pct (Nd0.9Dy0.1) (Fe0.77Co0.12Nb0.03B0.08)5.5+45 wt pct a-Fe were studied. It was found that substitution of Co for Fe could significantly improve the permanent magnetic properties of the nanocomposite magnets and typically, the maximum magnetic energy product was increased from 104.8 kJ/m3 (13.1 MGOe) to 141.6 kJ/m3 (17.7 MGOe). In contrast to the case of conventional nominally single-phase magnets, the addition of Nb results in promoting the growth of a-Fe grain and is thus unfavorable for the improvement of permanent magnetic properties of the nanocomposites. Although the addition of Dy can increase the coercivity of the magnets, the increase of magnetic anisotropy of hard phase leads to decrease of the critical grain size of soft phase. Additionally it causes the difficulty of preparing the nanocomposites because it is more difficult to control the grain size of soft phase to meet the requirement of appropriate exchange coupling between hard and soft grains. 相似文献
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S. M. A. Radmanesh S. A. Seyyed Ebrahimi 《Journal of Superconductivity and Novel Magnetism》2013,26(7):2411-2417
Magnetic hard/soft SrFe12O19/Ni0.7Zn0.3Fe2O4 nanocomposites were fabricated by a two-step chemical procedure. Strontium hexaferrite NPs were synthesized via sol–gel self-propagation and then dispersed in nickel–zinc ferrite sol to prepare oxide nanocomposites by the glyoxilate precursor method. The initial product was annealed at different temperatures to study the effect of grain size on the magnetic properties of composite hard/soft ferrites. The magnetic nanoparticles (MNPs) were characterized by XRD, FTIR, TEM, and VSM techniques. Magnetic measurements indicated concave hysteresis loops for these two-phase nanocomposites due to non-complete exchange coupling at the interfaces of hard and soft ferrites. This phenomenon could be attributed to the overcritical size, 46 nm, of the hard phase, based on the critical limit of 22 nm predicted by theoretical calculation. At high annealing temperature with increasing the size of the soft phase as well as the hard phase, the dipolar interaction became dominant and the magnetic behavior of hard/soft nanocomposites approached two-phase uncoupled magnets. 相似文献
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We have performed first-principles calculations to study the interfacial exchange coupling in a SmCo5/Co multilayer model system. The hard phase hcp SmCo5 and the soft phase hcp Co (or Co(1-x)Fe(x)) stacking along (1010) direction are structurally well matched. The atomic structure, including the alignment and the separation between layers, were optimized first. Then the non-collinear magnetic structures were calculated to explore the exchange coupling dependence on the variation of the atomic composition across the interface. We found that the inter-phase exchange coupling strength is strongly dependent on the interface condition between the hard and soft phase by comparing the exchange coupling strengths in different interface conditions. The findings were further confirmed by the calculated site-to-site exchange parameters across the interface. 相似文献
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Yang Y Pandey KK Chen JS Chow GM Hu JF 《Journal of nanoscience and nanotechnology》2011,11(3):2607-2610
In this work, effects of exchange coupling of soft magnetic layer on switching field and magnetization reversal behaviour of CoPt-SiO2(soft)/CoPt-SiO2(hard) exchange coupled media were investigated. With increasing the thickness of the soft layer, both the coercivity and magnetization squareness of composite media decreased. Soft layer thickness 4 nm and below was more effective to significantly reduce the switching field than that above 4 nm. More incoherent switching behavior was observed with increasing soft layer thickness. 相似文献
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A new type of permanent magnet alloy with composition Nd9.32Fe85.32B5.36 has been prepared by a melt spinning method. After optimized annealing of the initial amorphous alloy, high magnetic properties are obtained in the isotropic specimens. Remanence, energy product and intrinsic coercivity are 1.09 T, 153.6 kJ m−3 and 400 kA m−1, respectively. The samples consist of two phases, a matrix of nanometer-sized hard magnetic Nd2Fe14B phase (about 40 nm) together with numerous -iron particles (about 20 nm) embedded in it. The crystallization behavior for amorphous samples has been studied. The results indicate that the -iron initially precipitates from the amorphous matrix, and at higher annealing temperatures the crystallization of the Nd2Fe14B phase occurs. No metastable phase was observed in all heat treatments. Although the volume fraction of the magnetically soft -iron is about 30 vol%, the second quadrant of the J-H loop is typical of a magnetically soft hard material. The role of exchange coupling between the magnetically soft grain and the magnetically hard grain is discussed. 相似文献
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Amorphous ribbons of composition Fe74.5-xCuxNb3Si13.5B9 (x =0, 1 at.%) have been annealed between about 500°C and 900°C. This produced a series of crystallized samples with grain sizes between about 10 nm and 300 nm and with coercivities H c and initial permeabilities μi varying over several orders of magnitude. The best soft magnetic properties (H c≈0.01 A/cm and μi≈80×103 ) were observed for the smallest grain sized of about 10 nm. With increasing grain size D , coercivity steeply increases following a D 6-power law (up to D≈50 nm). H c then runs through a maximum of H c≈30 A/cm and decreases again for grain sizes above 150 nm according to the well-known 1/D law for polycrystalline magnets. The initial permeability was found to vary in a similar manner, essentially being inversely proportional to coercivity. The variation of the soft magnetic properties with the average grain size is discussed and compared with the predictions of the random anisotropy model and other theories for the magnetization reversal 相似文献
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Chuanbing Rong Ying Zhang Narayan Poudyal Izabela Szlufarska Rainer J. Hebert M. J. Kramer J. Ping Liu 《Journal of Materials Science》2011,46(18):6065-6074
Fabrication of bulk nanocomposite materials, which contain a magnetically hard phase and a magnetically soft phase with desired
nanoscale morphology and composition distribution has proven to be challenging. Here we demonstrate that SmCo/Fe(Co) hard/soft
nanocomposite materials can be produced by distributing the soft magnetic α-Fe(Co) phase particles homogenously in a hard
magnetic SmCo phase matrix through a combination of high-energy ball milling and a warm compaction. Severe plastic deformation
during the ball milling results in nanoscaling of the soft phase with size reduction from micrometers to ~15 nm. Up to 35%
of the soft phase can be incorporated into the composites without coarsening. This process produces fully dense bulk isotropic
nanocomposite materials with remarkable energy-product enhancement (up to 300%) owing to effective inter-phase exchange coupling. 相似文献
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Heliang Qu JiangYu Li 《IEEE transactions on magnetics》2005,41(3):1093-1099
We report an effective medium theory of magnetization reversal and hysteresis in magnetically interacting particles, where the intergranular magnetostatic interaction is accounted for by an effective medium approximation. We introduce two dimensionless parameters, /spl lambda/ and h/sub 0/, that completely characterize the hysteresis in a ferromagnetic polycrystal when the grain size is much larger than the exchange length so that the exchange coupling can be ignored. The competition between the anisotropy energy and the intergranular magnetostatic energy is measured by /spl lambda/, while the competition between the anisotropy energy and Zeeman's energy is measured by h/sub 0/. The hysteresis loop, magnetostatic energy density, and anisotropy energy density calculated by using this theory agrees well with micromagnetic simulations. The calculations also reveal that the subnucleation field switching due to the magnetic field fluctuation is important when the magnet is not very hard, and that has been accounted for by a probability-based switching model. 相似文献