Influence of third elements on growth of Nb3Sn compounds and on global pinning force

The crystal growth of Nb₃Sn by the bronze method has been investigated by using diffusion couples consisting of niobium and bronze with the addition of third elements. When the specimens were annealed at temperatures between 973 and 1073 K, the time-dependence of layer thickness was represented approximately by the function ofd=kt ^m . The time exponent changed from 1/3 to unity depending on the annealing condition as well as on the nature of the third element. By the addition of titanium, hafnium, zirconium, indium and galium to the bronze, the growth rate of the compound layer increases. Faster layer growth corresponds to a larger time exponent. The following three processes are suggested to be important for controlling layer growth: diffusivity of tin atoms through grain boundaries in the compound layer, diffusivity of tin atoms through the matrix of the compound, and the rate of the chemical reaction to form the compound. Essentially these combined processes control the overall rate of layer growth. The grain size is found to be the most effective structural parameter to affect directly the maximum global pinning force. The critical current at a magnetic field of 5T can be scaled by both the layer thickness and the inverse grain size.     

Effect of high magnetic field on the morphology of (Cu, Ni)6Sn5 at Sn0.3Ni/Cu interface

The effect of high magnetic field on the microstructure of (Cu, Ni)₆Sn₅ intermetallic compound layer in Sn0.3Ni/Cu couples at 250 °C was examined. The applied magnetic field changed the morphology of outer (Cu, Ni)₆Sn₅ crystals on the Sn side from faceted shape to stick shape. The high magnetic field affected the crystal orientations of (Cu, Ni)₆Sn₅ and reduced the Ni content in the outer layer. The morphology evolution of (Cu, Ni)₆Sn₅ is attributed to the content of Ni solute decreased by magnetic field. The effects of high magnetic field on the liquid convection and phase diagram are considered to be responsible for the Ni content.     

稳恒强磁场对Al-Cu扩散偶界面中间相形成和生长的影响

研究了稳恒强磁场作用下Al-Cu扩散偶界面中间相组成和扩散行为.结果表明:强磁场作用下扩散偶中间相厚度显著增加,并且随磁场强度增大,界面中间相组成发生变化.按照抛物线规律计算了强磁场作用下扩散偶中间相的扩散系数,发现在平行和垂直于磁场的两个方向上扩散系数有显著差异,垂直于磁场方向的扩散系数比平行于磁场方向更大.强磁场促进了Al-Cu扩散偶中Al和Cu原子的扩散,加速了界面中间相的形成和生长过程.磁场作用差异导致了扩散的各向异性.利用原子扩散理论初步分析了产生上述现象的原因.     

交变磁场对高硬熔覆层成型质量的影响

为改善激光熔覆高硬熔覆层的成型质量,外加辅助交变磁场是行之有效的方法。本工作设计了一种可调频、调幅的简易机械式类正弦交变电磁场发生装置,在激光熔覆过程中辅助施加了类正弦交变磁场,通过改变磁感应强度和交变频率,在Q235A表面制备了单道和多道高硬合金熔覆层,通过对熔覆层的宏、微观检测,研究了交变磁场对熔覆层几何特征、稀释率和微观组织的影响。研究结果表明,当磁场频率和磁感应强度变化时,熔覆层宽度波动范围很小,且平均值基本保持不变;熔覆层高度和接触角随着磁感应强度的增大而减小;稀释率的大小基本不受磁场参数变化的影响;在磁场作用下,熔覆层中气孔向熔覆层表面迁移,熔融金属对流加剧,粗大枝晶破断,熔覆层组织更加均匀致密。     

Si作过渡层的Co/Cu/Co三明治膜中高灵敏度巨磁电阻效应和平面内磁各向异性

用高真空电子束蒸发方法制备了以半导体材料Ｓｉ 为过渡层的Ｃｏ／Ｃｕ／Ｃｏ三明治膜并研究了其巨磁电阻效应。当Ｓｉ 过渡层厚度达到０．９ｎｍ 时,三明治膜中开始出现较强的平面内磁各向异性。在Ｓｉ１．５ｎｍ／Ｃｏ ５ｎｍ／Ｃｕ ３ｎｍ／Ｃｏ ５ｎｍ结构中,在其易轴上得到了５ ．５％ 的巨磁电阻值和０．９ ％／Ｏｅ 的高磁场灵敏度。研究了过渡层Ｓｉ／Ｃｏ 界面之间的相互扩散,发现在过渡层Ｓｉ 与Ｃｏ 层间形成了ＣｏＳｉ 化合物。这个硅化物界面层诱导了三明治膜的平面内磁各向异性,从而导致了易轴上高灵敏度巨磁电阻效应。     

Suppression of damage to organic light-emitting layers during deposition of Al-doped ZnO thin films by radio-frequency magnetron sputtering

Conditions for deposition of Al-doped ZnO (AZO) films on an organic light-emitting layer with a radio-frequency magnetron sputtering system were optimized to realize high deposition rate and low resistivity of the films. Damage inflicted on the organic layer by depositing the AZO film under the optimized deposition conditions was studied from photoluminescence, UV-Vis and Fourier transform infrared spectroscopy spectra using tris(8-hydroxyquinolinato)aluminium as a model organic compound. We found that damage to the organic layer was lessened by increasing the magnetic field from a normal intensity of 0.02 T to 0.1 T. The damage to the organic layer was further lessened by inserting a grounded grid electrode between a target and the substrate.     

The effect of an oblique magnetic field on the surface instability of a finite conducting fluid layer

Summary The effect of an oblique magnetic field on the growth rate of Rayleigh-Taylor instability (RT) at the interface of a finite thickness layer of a viscous electrically conducting fluid in the presence of surface tension has been studied analytically. The effects of aligned and transverse magnetic fields on the coupled differential equations for the velocity and the magnetic field are discussed separately. The numerical results reveal that the nature and strength of the magnetic field and the layer thickness exacerbate or ameliorate the instability characteristic of such a layer.     

Magnetic properties of BaFe12O19 smallparticles

The magnetic properties of small BaFe₁₂O₁₉ particles about 50 nm in size have been studied; the emphasis was on small-size effects. The compound formation of the hexagonal structure was made at a relatively low temperature; the small particle size made this result possible. As compared to the bulk value, a significantly reduced saturation magnetization is observed for these particles; this agrees with similar reports made earlier by several authors. To examine these phenomena further, Mossbauer spectra were obtained with high magnetic field applied longitudinally (H_ex=16.4 and 50 kOe). The spectra show the presence of recalcitrant spins where the spin configuration has a noncollinear arrangement that even a 50-kOe magnetic field does not remove. This hard-to-saturate component may lie in the surface layer of the Ba-ferrite small particles. The data also provide evidence that the Fe ions in the bipyramidal (2b) sites undergo magnetic-field-induced oscillations at 4.2 K     

CoFe/Cu/CoFe/IrMn自旋阀结构多层膜磁化反转过程的研究

通过高真空直流磁控溅射的方法制备了结构为//Ta(5nm)/Co75 Fe25(5nm)/Cu(2.5nm)/Co75Fe25(5nm)/Ir20 Mn80(12nm)/Ta(8nm)的顶钉扎自旋阀结构多层膜,研究了磁场循环次数、反向饱和场等待时间和磁场变化率对自旋阀结构多层膜磁化反转过程的影响.结果表明,磁场循环次数和反向饱和场等待时间对自由层的磁化反转过程没有影响,而在被钉扎层中出现了练习效应和时间效应;磁场变化率对被钉扎层和自由层的前、后支反转场的影响变化趋势相似,但反铁磁层对被钉扎层的反转有一定的影响.     

强磁场下Zn-2 wt.%Cu合金定向凝固的初步研究

本文进行了10T强磁场下Zn-2wt.%Cu合金的定向凝固的初步研究.结果发现下拉速度较低时,无磁场时晶体以平界面方式生长,而施加磁场则产生带状组织,并且随着磁场的增加带状组织越来越明显,带状组织间距越来越小;当定向凝固速度较高,晶体以枝晶方式生长时,磁场促进枝晶的分枝,并扰乱枝晶规则生长;随定向凝固速度提高,磁场的作用逐渐减弱.     

Growth of diffusion layers at liquid Al–solid Cu interface under uniform and gradient high magnetic field conditions

The effect of high magnetic fields on interfacial reactive diffusion in liquid/solid (Al/Cu) couples was experimentally investigated at a temperature of 973 K. Regardless of any magnetic field, compound layers consisting of the δ, ξ₂, η₂ and θ phases were produced at the interface. The magnetic flux density, B, exerted a non-monotonic influence on the growth of the diffusion layers. Moreover, the mean thickness of the diffusion layers (parallel to B) was found to be always greater than that of the diffusion layers (perpendicular to B) under the applied magnetic fields. These phenomena should be attributed to the effects of two types of the Lorentz force under a uniform high magnetic field on diffusion behavior. In addition, the growth of intermetallic phases could be retarded by a magnetic field gradient due to the magnetic force in the axial direction.     

Influence of Alternative Magnetic Field on the Diffusion of Al and Mg

The influence of an alternative magnetic field on the diffusion of Al and Mg in AI-Mg diffusion couple is studied. The diffusion zone is composed of two intermediate phases, namelyβ and γ phase. Thickness of each intermediate phase is examined. The results show that the alternative magnetic field increases the thicknesses of βand γ phase zone and the layer growth ofβ and γphase obeys the parabolic rate law. The growth rate of the β and γ phase are increased with the application of the alternative magnetic field. This change is manifested through a change in the frequency factor k0 and not through a change in the activation energy Q. The frequency factor k0 for intermediate phase growth with an alternative magnetic field is 39.95 cm2/s for 7 phase and 2.84×10-4 cm2/s for β phase compared with those without the magnetic field is 22.4 cm2/s for 7 phase and 1.53×10-4 cm2/s for β phase.     

Tunable magnetic properties by interfacial manipulation of L1(0)-FePt perpendicular ultrathin film with island-like structures

Based on interfacial manipulation of the MgO single crystal substrate and non-magnetic AIN compound, a L1(0)-FePt perpendicular ultrathin film with the structure of MgO/FePt-AIN/Ta was designed, prepared, and investigated. The film is comprised of L1(0)-FePt "magnetic islands," which exhibits a perpendicular magnetic anisotropy (PMA), tunable coercivity (Hc), and interparticle exchange coupling (IEC). The MgO substrate promotes PMA of the film because of interfacial control of the FePt lattice orientation. The AIN compound is doped to increase the difference of surface energy between FePt layer and MgO substrate and to suppress the growth of FePt grains, which takes control of island growth mode of FePt atoms. The AIN compound also acts as isolator of L1(0)-FePt islands to pin the sites of FePt domains, resulting in the tunability of Hc and IEC of the films.     

Increasing thermomagnetic stability of composite superconductors with additives of extremely-large-heat-capacity substances

We have studied the thermomagnetic stability (with respect to magnetic flux disturbances) of composite superconductors screened by additives of rare earth compounds possessing extremely high heat capacity at low temperatures. Three tubular composite structures have been manufactured and studied with respect to screening of the central region from variations of an external magnetic field. The effect of large-heat-capacity substances (LHCSs) was evaluated by measuring a jump in the magnetic flux in response to the rate of variation (ramp) of the external magnetic field. It is established that the adiabatic criterion of stability (magnetic-flux jump field) in the sample structures containing LHCSs significantly increases—by 20% for HoCu₂ intermetallic compound and 31% for Gd₂O₂S ceramics—as compared to the control structure free of such additives.     

Low temperature growth of carbon nanotubes in a magnetic field

We report on the growth of carbon nanotubes on a glass substrate at a low temperature of 450 °C by plasma-enhanced chemical vapor deposition in the presence of a magnetic field. The growth of carbon nanotubes can be realized at 450 °C only when a magnetic field is applied to the substrate. Carbon nanotubes cannot be grown in the absence of a magnetic field at the same temperature. An NH₃ plasma pretreatment significantly improved the uniformity of the grain size of the Ni catalyst under the magnetic field. The enhancement in the growth of CNTs at low temperature can be attributed to the magnetic moment pre-alignment of the ferromagnetic catalyst film under high magnetic field. A high emission current density of 20 mA/cm² was obtained at 6 V/μm and a stable emission current was observed. This method permits the growth of carbon nanotubes directly on glass substrate at much more reliable low temperatures for the fabrication of high-density field emitter arrays.     

Study of Magnetic Field-Assisted ED Machining of Metal Matrix Composites

The present study deals with an investigation of the hybrid electric discharge (ED) machining process executed in a magnetic field for improving process performance. Previous magnetic field-assisted electric discharge machining (MFAEDM) techniques, however, are limited to use with a class of magnetic workpieces. In this particular study, the magnetic field was coupled with the conventional EDM plasma zone to test the hybrid process on Al-based metal matrix composites (MMCs). The machining parameters, for instance, peak current as well as duration of pulse-on were selected to nail down thereafter effects on the response parameters like the material removal rate (MRR) and the surface integrity. The experimental results show an improvement of 12.9% MRR and reduction in recast layer formation at higher spark energy in the magnetic field environment. As the experimental outcome implied that the MFAEDM imparted appreciable process stability, a highly efficient pertinent process of EDM with high quality of the machined surface could be accomplished to satisfy modern industrial applications.     

Three dimensional dendritic morphology and orientation transition induced by high static magnetic field in directionally solidified Al-10 wt.%Zn alloy

Effect of high static magnetic field on the dendritic morphology and growth direction in directionally solidified Al-10 wt.%Zn alloy were studied by three-dimensional (3D) X-ray micro-computed tomography, Electron Back-scattered Diffraction (EBSD) and X-ray Diffraction (XRD). The application of high static axial magnetic field (5T) during directional solidification was found to destabilize the solid/liquid interface and cause the growth direction of dendrite deviate from thermal gradient, leading to irregular solid/liquid interfacial shape and cellular to dendritic morphology transition. The thermoelectric magnetic convection (TEMC) caused by the interaction of thermoelectric effect and magnetic field was supposed to be responsible for the transition. In addition, the EBSD and XRD results confirm that the preferred growth direction of α-Al was found to transform from the traditionally expected <100> to <110>. The dendrite orientation transition (DOT) in Al-10 wt.%Zn alloy can be attributed to the effect of applied magnetic field on the anisotropy of crystal during solidification. The result indicates the potential application of high static magnetic field in altering the morphology and preferred growth direction of dendrite during directional solidification.     

Effects of a high-gradient magnetic field on the migratory behavior of primary crystal silicon in hypereutectic Al–Si alloy

The migration of primary Si grains during the solidification of Al–18 wt%Si alloy under a high-gradient magnetic field has been investigated experimentally. It was found that under a gradient magnetic field, the primary Si grains migrated toward one end of the specimen, forming a Si-rich layer, and the thickness of the Si-rich layer increased with increasing magnetic flux density. No movement of Si grains was apparent under a magnetic field below 2.3 T. For magnetic fields above 6.6 T, however, the thickness of the Si-rich layer was almost constant. It was shown that the static field also played a role in impeding the movement of the grains. The primary Si grains were refined in the Si layer, even though the primary silicon grains were very dense. The effect of the magnetic flux density on the migratory behavior is discussed.     

The effect of a magnetic field on the linear growth rates of Bénard-Marangoni convection

We obtain explicit analytical expressions for the linear growth rates of the steady Bénard-Marangoni convection in a horizontal layer of electrically-conducting fluid with a deformable free upper surface in the presence of a uniform vertical magnetic field subjected to a constant temperature at its lower boundary. The leading order behavior of the marginal stability curve for the onset of steady Bénard-Marangoni convection is also given. The numerically-calculated linear growth rates showing the stabilizing effect of the magnetic field are presented.     

High Magnetic Field Inffuence on the Widmanst¨atten Transformation in High Purity Fe-0.36 wt% C Alloy

The influence of high magnetic field with different strength on the proeutectoid ferrite transformation in high purity Fe-0.36 wt% C during diffusional γ→α phase transformation was studied.It was found that the formation of acicular ferrite(i.e.Widmanst¨atten ferrite) was obviously suppressed by the applied high magnetic field.The stronger the magnetic field is,the more the ferrite grains elongating and aligning along the field direction will be.This is attributed to additional driving force for phase transformation and demagnetization effect introduced by the applied magnetic field.This is also considered to be related to the preferential growth of proeutectoid ferrite nuclei along field direction caused by magnetic dipolar interaction.