纯石墨粉对NdFeB烧结磁体的显微组织和磁性能的影响

主要研究了在烧结ＮｄＦｅＢ磁体的晶界添加Ｃ对显微组织和磁性能的影响。实验表明，随Ｃ添加量的增大，晶粒先粗化再细化，矫顽力呈先下降后上升再下降的趋势当Ｃ一达到０．４％ｗｔ时，晶界变得零乱而不规整。Ｘ射线衍射分析表明此时磁体内生成了Ｎｄ２Ｆｅ１７Ｃ相，矫顽力和晶粒尺寸的变化均与Ｎｄ２Ｆｅ１７Ｃ的生成有关。     

HDDR工艺各向异性Nd（Fe,Co）B粘结磁体的磁性与取向磁场的关系

研究了取向磁场对ＨＤＤＲ工艺制备的各向异性Ｎｄ（Ｆｅ,Ｃｏ）Ｂ粘结磁体永磁性能的影响,实验指出采用ＨＤＤＲ工艺制取的含Ｇａ的Ｎｄ（Ｆｅ,Ｃｏ）Ｂ磁粉具有较强的各向异性。在用这种磁粉制备粘结磁体时,随着施回报以向磁场强度的逐渐增强,磁体的剩磁,矫顽力和磁能积不同程度地增大,其永磁性能明显提高。     

烧结NdFeB磁体的晶粒取向和矫顽力的角度关系

本文研究了烧结ＮｄＦｅＢ磁体的晶粒取向矣矫顽力的影响和矫顽力的角度关系，结果表明：晶粒的混乱取向使矫顽力上升而不是下降，矫顽力的发动场理论比成核机制和钉扎机制与实验结果符合更好。     

晶粒取向与烧结NdFeB磁体的磁性能

研究了烧结ＮｄＦｅＢ磁体的硬磁性能与晶粒取向程度的关系，结果表明：随着晶粒取向程度的增强，磁体的剩余磁极化强度Ｊｒ单调上升、内禀矫顽力ｊＨｃ单调下降，磁感矫顽力ＢＨｃ先上升，达到一极大值后下降，从而导致了最大磁能积（ＢＨ）ｍａｘ的饱和行为。应用矫顽力的发动场理论很好地解释了这一实验现象。     

添加低熔点Nd-Cu合金对纳米晶热压Nd-Fe-B磁体的影响

采用钕铁硼快淬磁粉和低熔点Nd-Cu合金混粉热压/热流变的方法,制备出的各向异性磁体矫顽力从747kA/m提高到1 280kA/m。XRD图谱表明样品取向度随合金添加量增大逐渐减小。通过SEM和TEM图片发现添加的Nd-Cu主要分散在晶界中,使得平均晶粒尺寸减小,各向异性热流变磁体晶界变厚,静磁耦合作用减弱,矫顽力得到明显提升。     

各向异性HDDR工艺Nd(Fe,Co)B粘结磁体的反磁化过程和矫顽力

研究了取向磁场对ＨＤＤＲ工艺制备的各向异性Ｎｄ（Ｆｅ,Ｃｏ）Ｂ粘结磁体顽力的影响。实验指出：阴着施加取向磁场强度的逐渐增强,磁体的制磁和矫顽力不同程度的增加。磁体的反磁化过程包括晶粒内部的成核过程和晶粒之间的畴壁位移过程,矫力应由两种反磁化过程的共同作用决定。     

表面处理对粘结钕铁硼永磁的抗氧化性研究

本文研究了微观处理和宏观处理对钕铁硼的抗氧化性影响，结果表明偶联剂微观保护ＮｄＦｅＢ磁粉和环氧涂层宏观保护粘结ＮｄＦｅＢ磁体相结合的办法可显著提高塑料粘结ＮｄＦｅＢ永磁的抗氧化性。     

掺杂Dy2O3Nd—Fe—B磁体的氧含量对磁性能的影响

用穆斯堡尔效应和磁性测量等方法，研究了掺杂Ｄｙ２Ｏ３Ｎｄ－Ｆｅ－Ｂ磁体的氧含量对磁性能的影响以及氧含量与掺杂浓度和制粉球磨时间的关系。结果表明，掺杂Ｄｙ２Ｏ３可以有效地提高磁体的矫顽力，但其剩磁和最大磁能积会不同程度地低。磁体中的氧含量由掺杂浓度和制备工艺所决定，并满足一定关系式。当掺杂浓度为１．０ｗｔ／时，磁性能在氧含量为１１０００ＰＰｍ附近发生突变。     

微晶钕铁硼真空快淬设备及工艺研究

本文结合国内外钕铁硼永磁材料的开发应用状况，采用熔体旋转萃取法，设计、制造并调试完成了一台 ＶＲＱ－１０Ｔ型真空快淬设备，合理地选择了工艺参数，得到了厚为 ２０～５０μｍ的 ＮｄＦｅＢ薄带，制备了最大磁能积（ＢＨ）ｍａｘ＝５１．７ｋＪ／ｍ３的ＮｄＦｅＢ粘结磁体．本文介绍了该设备各部件的结构特点，并通过对退磁曲线的测试和对Ｘ射线衍射图样的观察，分析了影响微晶 ＮｄＦｅＢ成带情况及粘结 ＮｄＦｅＢ磁体性能的各种因素。最后，我们得到结论．转轮表面线速度是影响磁性能的主要因素，微晶结构的ＮｄＦｅＢ粘结磁体性能最佳．     

NdFeB永磁的晶界调控和晶界扩散技术

NdFeB永磁在电机等领域的应用要求磁体不仅具有足够高的矫顽力和磁能积,还要求高的热稳定性。在提高NdFeB磁体的综合磁性能的同时降低材料成本也是非常现实的问题。因此,通过成分优化、微观组织调控和新工艺开发来提高材料性价比是NdFeB永磁的主要研究方向。本文介绍了国内外通过晶界成分和结构调控来降低NdFeB磁体的稀土含量和提高矫顽力的部分研究进展,报道了我们在晶界调控和晶界扩散方面的最新研究结果。通过调整和优化烧结与热处理工艺可以有效地光滑和清洁晶界;通过添加微量元素也可以调控晶界结够;而采用晶界扩散新技术可以将Dy或其他稀土扩散至晶界。这些工艺可以在降低NdFeB永磁稀土含量的同时,有效地提高材料矫顽力和综合硬磁性能。     

Magnetic properties of immiscible Co-Ag and Ni-Ag thin films prepared by co-sputtering

Magnetic properties of immiscible Co-Ag and Ni-Ag thin films prepared by co-sputtering have been investigated. Saturation magnetizations of the films decreased linearly with increasing Ag concentration. Although the coercivity of Ni-Ag thin film does not vary with addition of Ag, the coercivity of Co-Ag thin film rises to reach a maximum at 41% Ag. The coercivity of Co-41% Ag thin film increases with annealing over 250° C. The thin films all have a fine grain structure. The average grain diameters of Co-Ag thin films and their coercivities increase with annealing. Moreover, it was found that the coercivity and average grain diameter have a linear relation. Therefore, as one reason for a coercivity increase with annealing, it is thought that the phenomenon is caused by the growth of Co grains in the film.     

Relationship between microstructure and magnetic domain structure of Nd--Fe--B melt-spun ribbon magnets

The relation between the microstructure, observed using an electron probe microanalyzer, and the domain structure, observed using a Kerr microscope, was established to evaluate the effects of hot rolling and the addition of Ti--C on the c-axis orientation and the magnetization process of hot-rolled Nd--Fe--B--Ti--C melt-spun ribbons. The addition of Ti--C promotes the c-axis orientation and high coercivity in the ribbons. Elemental mapping suggests a uniform elemental distribution; however, an uneven distribution of Ti was observed in an enlarged grain with Ti-enriched points inside the grain. The reversal domains that nucleated at the Ti-enriched point inside the grain cause low coercivity.     

Effect of capped layer on microstructure and magnetic properties of FePt films

Sputter-deposited FePt films exhibit an in-plane magnetic anisotropy when MgO is used as the capped layer. The perpendicular magnetic anisotropy of FePt films can be enhanced by introducing a Ag capped layer instead of a MgO capped layer. Although the in-plane coercivity (Hc_//) of FePt films decreases slightly after introducing a Ag capped layer instead of a MgO capped layer, the perpendicular coercivity (Hc_⊥) is increased significantly from 3169 Oe to 6726 Oe. Auger electron spectroscopy analysis confirms that Ag atoms diffuse from the capped layer into the FePt magnetic layer and are mainly distributed at the grain boundary of FePt. This phenomenon results in enhancement of the grain boundary energy and inhibition of grain growth, thus increasing the perpendicular coercivity and reducing the grain size of the FePt film.     

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。     

Reduction of Coercivity of Fe-N Soft Magnetic Film by Heat Treatment

200 nm thick Fe-N magnetic thin films were deposited on glass substrates by RF sputtering. The as-deposited films havehigh saturation magnetization but their coercivity is also higher than what is needed Therefore it is very important to reducecoercivity.The samples were vacuum annealed at 250℃ under 12000 A/m magnetic field. When the N content was in therange of 5～7 at. pct, the thin films consisted of α'+α" after heat treatment and had excellent soft magnetic properties of4πM_s=2.4 T, H_C<80 A/m. However, the thickness of a recording head was 2 μm, and H_c increased as thickness increased.In order to reduce the H_c, the sputtering power was raised from 200 W to 1000 W to reduce the grain size. 2 μm Fe-N thin     

Interactions of magnetic domain walls with twin and grain boundaries in orthoferrites

Twin and grain boundaries impede the motion of magnetic domain walls in the orthoferrites. Bubbles distort and collapse before it is possible to propagate them through twin boundaries and all but very low angle grain boundaries. A new experimental technique has been used to measure the coercivity of isolated defects in nearly perfect crystals. The coercivity measured is the minimum applied field required to force a planar domain wall past a defect. Models of the spin configurations near twin and grain boundaries in the presence and absence of magnetic domain walls have been developed to explain the observed coercivities.     

The effect of Cu substitution on the microstructure and magnetic properties of MnFe2O4 ferrite

The effect of compositional variation on grain size and porosity of Mn_{1 – x} Cu _x Fe₂O₄ ferrite, where x = 0.0, 0.25, 0.50, 0.75, 1.00, prepared by standard ceramic method are reported. From microstructure analysis it follows that porosity increases with the Cu concentration where as coercivity increases up to x = 0.50. Above x = 0.5 the decrease in coercivity is explained on the basis of Neel's mathematical model treating the demagnetizing influence of non-magnetic material in cubic crystals. The coercivity, varies inversely with the grain size upto x = 0.5. The decrease in coercivity above x = 0.5 with grain size can be correlated with the inter-granular domain wall movement because of large porosity.     

磁控溅射沉积Cu-W薄膜的特征及热处理的影响

采用磁控共溅射法制备含钨1.51%~14.20%(原子分数,下同)的Cu-W合金薄膜,并用EDX、XRD、SEM、显微硬度仪和电阻仪研究了其成分、结构及性能。结果表明,添加W可显著细化Cu-W薄膜基体相晶粒,晶粒尺寸随W含量的增加而减小,Cu-W薄膜呈纳米晶结构。Cu-W薄膜中存在W在Cu中形成的fcc Cu(W)非平衡亚稳过饱和固溶体,固溶度随W含量的增加而提高,最大值为10.65%。与纯Cu膜对比发现,薄膜的显微硬度和电阻率总体上随W含量的增加而显著增大。经200℃、400℃及650℃热处理1h后,Cu-W薄膜基体相晶粒长大,EDX分析显示晶界处出现富W第二相;薄膜显微硬度降低,电阻率下降,降幅与退火温度呈正相关。添加W引起的晶粒细化效应以及退火中基体相晶粒度增大分别是Cu-W薄膜微观结构和性能形成及演变的主要原因。