双三次样条插值法的磁熵变计算系统的研究

本文详细探讨了基于双三次样条插值法的磁熵变（△SM）计算方法，并通过软件实现；该方法与传统方法相比，可更精确地找到最大磁熵变，计算速度大大提高，为磁制冷材料提供了更准确的依据。     

机械合金化制备GdSiGe系合金

具有巨磁热效应的材料GdSiGe系合金的发现，为室温磁制冷的实用化走出了关键性的一步。由于GdSiGe系合金在外场强度3T以下及30—300K的温度范围内都具有巨磁热效应，这样可以利用NdFeB等永磁体产生的外磁场作为制冷循环的外场，而不必用价格昂贵的超导磁场，使室温磁制冷实现及实用化成为可能。而GdSiGe系合金材料主要是利用熔炼法制备，这样将带来复杂的复合化工艺；利用机械合金化制备可减少复合化工艺，并提高磁性能。论文主要探讨机械合金化的优化工艺参数。     

NdFeBAlDyNb磁性能及抗海水腐蚀研究

针对通常用合金化法提高烧结NdFeB磁体耐蚀性的同时使磁性能严重下降的问题,提出了通过元素Dy、Nb复合添加的方法,提高磁体耐蚀性和磁性能.结果表明,同时添加Dy、Nb元素,不仅可以大幅增加磁体矫顽力,而且能削减Dy元素添加对剩磁降低的不利影响,使磁能积增大;当w(Dy)=1.0%,w(Nb)=0.8%时的磁体显微结构较好、综合磁性能优异.磁体耐蚀性随着Dy、Nb元素添加量的增大而提高.因此通过元素复合添加,可以提高磁体磁性能及耐腐蚀性,使其能广泛应用于腐蚀环境.     

多电平变流器多载波PWM技术的研究

针对通常用合金化法提高烧结NdFeB磁体耐蚀性的同时使磁性能严重下降的问题，提出了通过元素
Dy、Nb复合添加的方法，提高磁体耐蚀性和磁性能.结果表明，同时添加Dy、Nb元素，不仅可以大幅增加
磁体矫顽力，而且能削减Dy元素添加对剩磁降低的不利影响，使磁能积增大；当w(Dy)=1.0%，w(Nb)=0.8%
时的磁体显微结构较好、综合磁性能优异.磁体耐蚀性随着Dy、Nb元素添加量的增大而提高.因此通过元素
复合添加，可以提高磁体磁性能及耐腐蚀性，使其能广泛应用于腐蚀环境.     

热处理对Gd_(0.6)Dy_(0.4)Co_2和Gd_(0.6)Dy_(0.4)Co_(1.9)Al_(0.1)合金磁热性能的影响

用真空电弧熔炼炉制备Gd0.6Dy0.4Co2和Gd0.6Dy0.4Co1.9Al0.1合金,在900℃下进行4天、7天的热处理后,对其铸态和热处理态的相结构、居里温度、绝热温变、磁熵变等进行了研究。结果表明:经过7天的热处理后合金晶体结构基本变为单相GdCo2结构。热处理的结果使合金的最大绝热温变值比铸态合金有所升高,磁熵变值比铸态合金提高53.2%和33.1%,居里温度略有降低,说明热处理能有效提高该系列合金的磁热性能。     

Nd8-xDyxFe82Co6B4纳米复合永磁材料的磁性能

针对NdFeB纳米复合永磁材料的矫顽力偏低的现状,采用熔体快淬法制备了Nd8DyxFe82Co6B4（x=0,0．4,0．8,1．2,1．6）纳米复合永磁材料,研究了Dy和Co的添加对NdFeB纳米复合永磁材料的磁性能的影响．研究结果表明,Dy的添加可提高材料的各向异性场,提高矫顽力,但是Dy元素的添加使材料的剩磁降低,结晶温度升高,因此添加量不宜过多;复合添加Co原子不仅可以提高材料的剩磁和矫顽力,而且可以弥补只添加Dy元素使材料的结晶温度升高的缺陷．在最佳的热处理条件下,Dy含量x=0．8时的样品表现出最佳的磁性能,矫顽力jHc=524kA／m,剩磁Br=1．11T,最大磁能积（BH）max=158kJ／m^3．     

近室温磁制冷工质的研究现状与发展前景

基于稀土－过渡金属间化合物Gd-Si-Ge系合金及钙钛矿型猛氧化物的磁热应及其巨磁热效应机理，对近室温磁制冷材料的研究现状及材料与磁制冷技术的发展前景进行了分析。     

球磨法制备(Gd0.9Dy0.1)5Si4粉末及分析

采用行星式球磨机进行磁制冷材料（Gd0.9Dy0.1)5Si4的纳米粉末制备，在一定的球磨条件下，一定范围内颗粒粒度与球磨时间成正比，并最终制备出纳米级颗粒，但在此过程中，磁性材料的磁性完全消失，估计是由于材料的晶体结构转变为非晶状态和应力共同作用所致。     

机械合金化Fe74.5Nb3Si13.5B9合金微观结构及磁性能

研究了Fe74.5Nb3Si13.5B9的机械合合金化过程，并对其机械合金化的机制进行了探讨，研究表明Fe74.5Nb3Si13.5B9经高能球磨20h可形成α-Fe固溶体纳米晶合金，球磨100h，纳米晶粒的平均尺寸为10nm左右，同时机械合金化使这些元素在铁中的固溶度在一定程度上得到了扩展。该合金的磁性能测定表明，其比饱和磁化强度和矫顽力分别达到了77.87Am^2/kg和125.6A/m.     

Tb0.3Dy0.7Fe1.95单晶的应用研究

用提拉法磁悬浮冷坩埚技术生长的 RFe2 (Tb0 .3Dy0 .7Fe1 .95)单晶材料 ,其室温下的饱和磁致伸缩系数 λs 可达2× 10 - 3以上 ,优于同成份的定向结晶材料。采用高性能 Tb0 .3Dy0 .7Fe1 .95单晶材料 ,通过优化微位移致动器的机械、磁路参数 ,研制出具有非水冷结构的新型微位移致动器。     

Influence of Tb substitution on low-field magnetocaloric effect in Gd5Si1.72Ge2.28 alloy

The lattice parameters, magnetic phase transition, Curie temperature and magnetocaloric properties for (Gd1-xTbx)5Si1.72-Ge2.28 alloys with x = 0, 0.15, 0.20 and 0.25 were investigated by X-ray powder diffractometry and magnetization measurements. The results show that suitable partial substitution of Tb in Gd5Si1.72Ge2.28 compound remains the first-order magnetic-crystallographic transition and enhances the magnetic entropy change, although Tb substitution decreases the Curie temperature (Tc) of the compounds. The magnetic entropy change of (Gd1-xTbx)5Si1.72Ge2.28 alloys retains a large value in the low magnetic field of 1.0 T.The maximum magnetic entropy change for (Gd0.80Tb0.20)5Si1.72Ge2.28 alloy in the magnetic field from 0 to 1.0 T reaches 8.7 J/(kg·K),which is nearly 4 times as large as that of (Gd0.3Dy0.7)5Si4 compound (|△Smax| = 2.24 J/(kg·K), TC = 198 K).     

Magnetic properties and XPS of Dy-Y and Dy-Nd alloys

The magnetic properties and X-ray photoelectron spectroscopy (XPS) spectra in the Dy100-xYx and Dy100-zNdz rare-earth alloys are studied.The magnetism measurements show that the dhcp crystal-field influence in the Dy-Nd alloys,which tends to destroy the orbital moment,does not vanish even though a field of 6T is applied.With increasing Y (or Nd) content the temperature region corresponding to helical phase becomes wider (or narrower).The XPS records suggest that the property of the valence fluctuation in neodymium tends to increase the Fermi wave vector kF of the Dy-Nd alloys.This testifies that the abrupt dropping of the Neel temperature,as Nd is introduced,is not only due to a dilution effect of Nd.The introduction of light rare earths into heavy ones is favorable for suppressing the helical phase in the alloys and overcoming the negative magnetocaloric effect.This result will play a guiding role in designing composite magnetic refrigeration working substances.     

Dy纳米粉含量对烧结Nd-Fe-B磁体的影响

为了改善烧结Nd-Fe-B磁体的磁性能和力学性能,采用二元合金法添加Dy纳米粉制备了高性能Nd-Fe-B磁体.利用扫描电子显微镜、X射线衍射仪、粒度分布仪、磁滞回线测试仪与维氏硬度仪对烧结Nd-Fe-B磁体的形貌、微观结构、化学成分、磁性能和力学性能进行了分析.结果表明,随着Dy元素质量分数的增加,磁体矫顽力大幅提高,剩磁和最大磁能积略有下降.相比未添加Dy元素的磁体,当Dy元素质量分数为0.8%时,磁体矫顽力提高了5.4%,剩磁和最大磁能积分别下降了1.3%和1.5%,维氏硬度提高了7.1%,此时磁体的综合磁性能最优.     

Effect of Dy substitution on the microstructure and magnetic properties of nanograin Nd-Fe-B single-phase alloys

Nanocrystalline single-phase alloys with the nominal compositions (at%) of Nd12.3-xDyxFe79.7Zr0.8Nb0.8Cu0.4B60 (x=0, 0.5,1.5, and 2.5) were prepared by melt-spinning and subsequent annealing. X-ray diffraction analysis shows that the as-spun ribbons were mainly com-posed of the amorphous phase. A slight content of Dy stabilizes the amorphous phase during annealing treatment. The grain size becomes smaller and the coercivity of the annealed ribbon is gradually improved with the increase of Dy content. Excessive Dy is harmful to the re-manence. It is found that no intergranular phase exists between the grains by high-resolution transmission electron microscopy, and the grain boundaries are crystallographically coherent in the optimally annealed sample. The optimum magnetic properties of remanence (Jr=1.09 T), coercivity (Hci=1048 kA/m), and maximum magnetic energy product ((BH)m=169.5 kJ/m3) are obtained from the x=0.5 ribbon in a post heat-treated state (700℃, 10 min).     

Influence of Tb substitution on low-field magnetocaloric effect in Gd5Si1.72Ge2.28 alloy

The lattice parameters, magnetic phase transition, Curie temperature and magnetocaloric properties for (Gd_1−x Tb _x )₅Si_1.72-Ge_2.28 alloys with x = 0, 0.15, 0.20 and 0.25 were investigated by X-ray powder diffractometry and magnetization measurements. The results show that suitable partial substitution of Tb in Gd₅Si_1.72Ge_2.28 compound remains the first-order magnetic-crystallographic transition and enhances the magnetic entropy change, although Tb substitution decreases the Curie temperature (T _C) of the compounds. The magnetic entropy change of (Gd_1−x Tb _x )₅Si_1.72Ge_2.28 alloys retains a large value in the low magnetic field of 1.0 T. The maximum magnetic entropy change for (Gd_0.80Tb_0.20)₅Si_1.72Ge_2.28 alloy in the magnetic field from 0 to 1.0 T reaches 8.7 J/(kg·K), which is nearly 4 times as large as that of (Gd_0.3Dy_0.7)₅Si₄ compound (|ΔS _max| = 2.24 J/(kg·K), T _C = 198 K). Foundation item: Project (50371058) supported by the National Natural Science Foundation of China     

Effect of Dy on Structure and Magnetic Properties of Dy_xFe_(60.5-x)Pt_(39.5) Alloys

Effects of the content of Dy on structure and magnetic properties of DyxFe60.5-xPt39.5 alloys(x = 0, 0.5, 1.0, 1.5) were investigated. The results of XRD analysis proved that the phase-transitional temperature of DyxFe60.5-xPt39.5 alloys from disordered face-centered-cubic structure to ordered face-centered-tetragonal cubic structure decreases with the increase of the content of Dy(x). Suitable content of Dy can improve the exchange coupling between soft magnetic phase and hard magnetic phase by refining gr...     

粉末Tb0.27Dy0.73Fe2的最佳磁粉粒度研究

从磁场取向和铁磁体磁化出发，研究了粉末Tb0.27Dy0.73Fe2的最佳磁粉粒度．计算结果表明：Tb0.27Dy0.73Fe2磁粉颗粒的单畴临界直径为22nm，磁粉粒度小于22nm时整个颗粒为单畴结构；磁粉粒度大于22nm时，磁粉将过渡到多畴结构．所以理论上粉末Tb0.27Dy0.73Fe2的最佳磁粉粒度为纳米数量级．理论值与实验值的偏离，主要是因为细颗粒磁粉比粗颗粒磁粉更容易氧化且细颗粒的浸润性较差．     

Dysprosium Modification of Cobalt Ferrite Ionic Magnetic Fluids

Dysprosium composite cobalt ferrite ionic magnetic fluids were prepared by precipitation in the presence of Tri-sodium citrate. Influence of dysprosium modification on magnetic property is studied. The result shows that magnetic response toward exterior magnetic field can be improved by adding Dy^3＋. Studies also show that the increase of reaction temperature may improve the modification effect of dysprosium. By adding dysprosium ions, the average diameter of the magnetic nanoparticles will be decreased evidently. It is clear that the particles appear as balls, Cobalt ferrite with sizes of 12-15 nm, rare earth composite cobalt ferrite with sizes of 6-8 nm.     

Magnetic properties of Fe3（1-x）Cr3xC alloys

The magnetic properties of Fe33(1-x)Cr3xC alloys with x=0.05, 0.1, 0.15, and 0.2, which crystallize in the cementiteFe3C-type structure with space group Pnma, were investigated by means of magnetization measurements. These alloys show tem-perature-induced second-order magnetic phase transitions. The Curie temperature (Tc) of these alloys decreases with increasing x. The isothermal magnetic-entropy changes of these alloys were derived from the magnetic isotherms measured with increasing tem-x = 0.05 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively.