碳纳米管磁化氢等离子体薄膜的微波吸收特性

为从理论上掌握有外加静磁场存在时铁催化高压歧化生成的碳纳米管中氢等离子体的微波吸收特性,根据磁离子理论和Appleton-Hartee方程,采用W.K.B近似方法,导出了碳纳米管磁化氢等离子体薄膜的微波衰减系数公式,数值计算了不同条件下碳纳米管磁化氢等离子体薄膜在0.3～30 GHz频段的微波衰减系数。研究结果表明:随着外加磁场强度的增加,Att30.00 dB/cm的频宽明显增大,吸收峰向高频方向移动.适当控制碳纳米管中等离子体的自由电子密度、电子碰撞的有效频率和外加磁场强度,能够实现碳纳米管中磁化氢等离子体薄膜对对特定微波段的强吸收.在外磁场等于0时,运用所构建的微波吸收模型得到的数值计算结果与已有的实验数据相吻合.     

Dynamic Modeling of Soft Magnetic Film Actuated Scanners

Dynamic behavior of magnetic thin film actuators is investigated in detail and applied to various laser scanning applications. Magnetic hysteresis effects are incorporated into the model developed in the prior work, which assumes linear magnetization as a function of magnetic field and is based on the distributed point-by-point calculation of the magnetostatic moments and forces across the film surface. A simple functional form is used to model the major $Bhbox{–}H$ loop of ferromagnetic films. The model is validated with permalloy (Ni-Fe) plated polymer actuators. The actuators are excited using an external electro-coil and the structures deflect due to magnetic anisotropy torque. The ac deflection of the actuators is modeled by calculating the point-by-point moments on the magnetic film and the solution can handle nonuniform external field and unsaturated magnetic film cases. A 25 $^{circ}$ optical scan angle is demonstrated for laser scanning display and imaging applications with a nonoptimum coil. Scaling the model to MEMS devices is also discussed.      

Domain wall generation and propagation in an amorphous ferromagnetic NiFeSiB film confirmed by the magneto-optical indicator film method

We employed the magneto-optical indicator film method to observe domain wall generation and propagation in NiFeSiB thin films. This method is sensitive to the magnetization directions on both surfaces as well as in the interior of the film. NiFeSiB has a lower magnetic anisotropy value compared to that of the CoFe and, therefore, it contains thicker domains. As an external magnetic field is strengthened, an increasing number of domains are generated and propagated into the interior. The use of a synthetic antiferromagnet layered structure leads to a reduction in both the value of the switching field and the number of domains generated as compared with the NiFeSiB single layer case, resulting from a reduction in the magnetostatic energy.     

薄膜高频磁阻抗效应及其应用

本文介绍了Ｆｅ－Ｎｉ软磁薄膜高频磁阻抗效应及在磁传感技术中的应用，分析了讨论了获得高灵敏度磁传感的途径，磁性薄膜厚度的一般控制在４００ｎｍ以上抑制Ｎｅｅｌ壁的出现，为了提高电压输出变化灵敏度，需要沿被测场方向加向Ｏｅ的偏磁场并使高频磁场形成闭合回路，感生各向异性通过在溅射薄膜过程中加几百Ｏｅ平行于膜的直流磁场获得，与各向异性磁阻效应和巨磁阻效应相比，高频磁阻抗效应传感技术灵敏度高，无巴克豪森噪声，     

条纹图形Heusler合金CoFeMnSi薄膜的制备及其磁特性研究

以CoFeMnSi作为研究对象,对其进行图形化设计,以研究图形化CoFeMnSi薄膜的磁学特性。利用感光溶胶-凝胶法和激光干涉法制得条纹图形ZrO2薄膜,之后利用磁控溅射法在其表面溅射沉积CoFeMnSi,以达到制得图形化CoFeMnSi磁性薄膜的目的,并对其表面形貌和磁学特性进行了表征。采用金相显微镜分析验证CoFeMnSi薄膜继承了ZrO2的条纹图形结构,条纹图形周期约为2μm;面内磁性测量显示薄膜398 kA/m磁场下的磁化强度与外磁场和条纹夹角θ呈180°周期性变化关系,且磁化强度介于390~440 kA/m;利用CoFeMnSi平膜面内磁化强度及面外磁化强度与外加磁场方向的变化关系,解释了条形薄膜磁化强度的θ角度依赖关系;采用磁力显微镜观察到磁畴结构形态为蜂窝状,磁畴尺寸大约1~2μm。     

Epitaxial Ni?Mn?Ga Films for Magnetic Shape Memory Alloy Microactuators

Active materials such as piezoelectrics are established in the field of microsystems application despite their low achievable strains which often require the integration of additional gear mechanisms. The ongoing search for new active materials has focused on magnetic shape memory (MSM) alloys such as Ni? Mn? Ga since they combine macroscopic strains of up to 10% with a cycling frequency well above the frequencies of conventional thermal shape memory alloys. The present review focuses on preparation and analysis of Ni? Mn? Ga films that can eventually be integrated in microsystems. Single crystal like films are prepared by epitaxial growth on suitable substrate materials. Since the magnetically induced reorientation of variants is blocked by a rigid substrate, we present different methods for releasing films from the substrates. We show that the sacrificial layer technology is the most promising approach. Further processing of the freestanding film requires a microtechnology which is adjusted to the film laminate structure. The properties of the freestanding films are compared with films on a rigid substrate. Although we observe stress‐induced twin boundary motion, the twinning stress is too high to be overcome by an external magnetic field. Therefore, it is necessary to develop suitable training methods to reduce the twinning stress below 2 MPa to enable the activation of the material by means of an external magnetic field.     

Pr2/3Sr1/3MnO3薄膜外场诱导自旋输运特性

采用脉冲激光沉积法制备了稀土掺杂钙钛矿锰氧化物Pr2/3Sr1/3MnO3(PSMO)外延薄膜,研究了薄膜在磁场、激光和电流作用下的自旋输运特性.在低温铁磁金属相,激光作用使薄膜的电阻增大,而磁场和电流则诱导电阻减小;在高温顺磁绝缘态,外场诱导均使电阻减小.在铁磁金属相,外场诱导输运特性的变化可归结于外场对体系电子自旋系统的影响:磁场和电流加强材料中eg电子和t2g局域电子间的自旋平行,增强了双交换作用;激光作用可产生光致退磁效应,减弱双交换作用.在顺磁绝缘态,场致电阻降低源于外场致使小极化子的退局域化效应.     

Asymmetric magnetoimpedance in two-phase ferromagnetic film structures

The magnetoimpedance of a film trilayer consisting of magnetically soft and magnetically hard films separated by a high-conductivity nonmagnetic spacer is theoretically investigated. A model for describing the dependences of the sample impedance on the external magnetic field and frequency is proposed, which is based on simultaneous solution of the linearized Maxwell and Landau–Lifshitz equations and takes into account the magnetostatic interaction between the magnetic layers. It is demonstrated that the magnetostatic interaction changes the distribution of magnetization of the magnetically soft film and leads to the occurrence of asymmetry in the field dependence of the impedance. The results obtained can be used in the development of weak magnetic field sensors.     

Magnetic field distribution in a ferromagnetic conductor

The magnetic field distribution in a cylindrical ferromagnetic conductor is determined for the case of a direct current flowing along the axis of the cylinder and a constant external magnetic field applied in a direction transverse to the current flow. The Gauss-Seidel iteration method is employed to obtain the vector potentials for different values of current and external field with the aid of a digital computer. The magnetic fields are then calculated from the resultant vector potentials. Calculations are carried out for currentI = 1.5A, radius of the cylindera = 2mm, and external magnetic fieldB_{0} = 0to 0.6 Wb/m².     

Micromagnetic Simulation of a Magnetic Film With Surface Roughness

We have simulated micromagnetically the static magnetic structure and magnetic spectrum of a magnetic film with surface roughness, using a finite stripe film model. We found that the rough surface can lead to a ripple magnetic structure, which results in increasing the damping factor of the film, and that the damping factor increases with the increase of the root-mean-square roughness. For a particular film with a given rough surface, the damping factor first decreases because of a decrease of the magnetic dispersion, then increases because of the surface-roughness-induced demagnetizing effect with increasing the external field.      

Deterministic Magnetization Switching Using Lateral Spin–Orbit Torque

Current-induced magnetization switching by spin–orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin–orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, deterministic current-induced SOT full magnetization switching by lateral spin–orbit torque in zero external magnetic field is reported. The Pt/Co/Pt magnetic structure is locally annealed by a laser track along the in-plane current direction, resulting in a lateral Pt gradient within the ferromagnetic layer, as confirmed by microstructure and chemical composition analysis. In zero magnetic field, the direction of the deterministic current-induced magnetization switching depends on the location of the laser track, but shows no dependence on the net polarization of external out-of-plane spin currents. From the behavior under external magnetic fields, two independent mechanisms giving rise to SOT are identified, i.e., the lateral Pt–Co asymmetry as well as out-of-plane injected spin currents, where the polarization and the magnitude of the SOT in the former case depends on the relative location and the laser power of the annealing track.     

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa₂Cu₃O_7?δ (YBCO) thin films have been deposited on bare and La_0.67Sr_0.33MnO₃ (LSMO) modified single crystal SrTiO₃ (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.     

Quenching of technical superconductors by heat and magnetic field pulses

The transition of a superconductor into the normal conducting state can be caused by external or internal disturbances. The initiation of normal conduction by external disturbances was investigated for technical superconductors by means of thermal and magnetic pulses applied locally to the superconductor. The dependence on transport current and matrix material respectively of the minimum energy and the minimum magnetic field to initiate normal conduction were determined. The conclusion was that the heat conducting along the superconductor has the most effective influence in stabilizing against thermal disturbances. The transition to normal conduction by magnetic field pulses could be explained by eddy current heating in the matrix. A 50 μm single core conductor was insensitive to the highest applied magnetic field pulses up to 0.3 T amplitude and a field rise of 75 Ts^?1 and consequently did behave according to the adiabatic stability criteria.     

Needleless electrospray of magnetic film from magnetization-induced cone array

Electrospray is a simple and versatile approach to deposit thin-films. Traditionally, electrospray is achieved through capillary nozzle electrode to create fluid jet. Here, we report a novel needleless electrospray approach to continuously deposit the magnetic film from the magnetization-induced self-assembling cone array of poly(vinyl pyrrolidone) (PVP)/Fe₃O₄ ferrofluid without any nozzle and feed unit. A spiral tower is used to pump the PVP/Fe₃O₄ ferrofluid and a 3D peak-cluster is self-assembled on the tip surface under an external magnetic field. The multiple and parallel jets can be continuously emitted from the cone array of 3D peak-cluster, and get deposited on the aluminum foil as a smooth magnetic film when a high-voltage electric field is further applied. This needleless electrospray approach is simple, and cost-effective with a high productivity. The prepared magnetic film mainly composed of Fe₃O₄ nanoparticles and PVP polymer exhibits superparamagnetic property and good magnetic field responsive property.     

Temperature and field dependence of superconducting thermometer sensitivity

We present empirical functions which relate the sensitivity of thin film superconductive thermometers to variations in temperature and external magnetic field. A formula is given which, by relating the sensitivity to the temperature dependence of the critical field, can be used to simplify thermometer calibration.     

Effect of external magnetic field on the deposition of BaFe12O19

The contribution of an external magnetic field on the deposition of BaFe₁₂O₁₉ thin film was investigated. For this purpose, two (one with applied field and another without field) thin films of BaFe₁₂O₁₉ were deposited on the C-plane oriented sapphire (Al₂O₃) substrate employing pulsed laser deposition technique. Crystallographic orientation and texture were determined using an X-ray diffractometer. The magnetic parameters were deduced from a vibrating sample magnetometer (VSM). A spectrometer was used to study the optical properties of the films. The structural results reveal the film to be predominantly single phase with C-plane orientation in both the cases. The film deposited with field, however, has bigger grain size and more perfection in crystallinity. The magnetic parameters show that the film deposited with the field has more remanence magnetization and higher coercive field. The diffuse reflectance of the film deposited with field is much higher due to the increased grain size and roughness.     

磁控挤压油膜阻尼器转子系统动力特性试验研究

为了改善传统挤压油膜阻尼器动力特性不可控的不足，提出了一种通过电磁效应来控制挤压油膜阻尼器动力特性的新结构，在一个双盘柔性转子系统上测量了不同磁场强度条件下磁控挤压油膜阻尼器转子系统在非旋转状态下的传递函数、在恒定转速下的运动轨道以及在慢加速运行过程中的不平衡响应曲线。结果表明了这种新型磁控挤压油膜阻尼器不仅具有良好的特性可控性，而且在设计合理的条件下还能够显著地减小转子系统的振动，是一种被动和主动兼备、具有良好发展和应用前景的转子系统阻尼结构。     

Heat transfer and resistance to movement in a rotationally advancing flow of conducting liquid in the presence of a magnetic field

Conclusions The functional relationships thus obtained for the resistance and heat-transfer coefficients in a rotationally-advancing flow of a conducting liquid in a pipe with a constant internal axial magnetic field and small Reynolds magnetic numbers (Re_m1) contains only a single longitudinal magnetic field strength component equal in the above case to the external magnetic field strength. It follows from the above that the formulas thus obtained hold both in the case when the flowing liquid does not perform any useful work, i.e., when electrical energy is not tapped off (or injected) in the form of a current, and for the case when it is tapped off (or injected).The difference consists only in the fact that in the second instance the velocity of the liquid drops along the pipe according to the amount of the work thus obtained (and, obviously, to the work in overcoming the resistance forces). In the first instance the reduction in the velocity is due only to the overcoming of the resistance forces.It is appropriate to note that formulas (17), (18), (20), and (21) for H_o=0 are converted into corresponding formulas for a rotationally-advancing liquid flow in a pipe without a magnetic field. The latter formulas are adequately confirmed by practical experience (see [2]). This provides grounds for assuming that the formulas will also be fully confirmed in practice.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 41–45, May, 1968.     

Magnetic field measurement near a superconducting film using a 2-dimensional field-dependence of Josephson current through a Nb tunnel junctions sensor

Two-dimensional (2-D) magnetic field dependences of Niobium/niobium tunnel junction current Ic were first used in order to measure the magnetic field near the superconducting film. The 2-D magnetic field dependences of superconducting Josephson current Ic through the niobium/niobium tunnel junction can be changed by the external magnetic field. So, we measured the magnetic field using this superconducting tunnel junction fabricated by DC-magnetron apparatus as a magnetic sensor. The 2-D magnetic field dependences of Ic through the junction without and with the Nb thin-film sample were compared. With the Nb thin-film sample, extension of the characteristics in the perpendicular direction Hz to the sample was observed because of the Meissner effect of the superconducting thin-film sample. Moreover, the magnetic field Hz perpendicular to the Nb thin-film sample has been added in the triangle shape as a following sequence: (0)-(1000)-(0)-(2000)-(0)-(3000)-(0)-(4000)-(0)-(5000 A/m)-(0). Significant changes in the measured Ic-H (Hy,Hz) characteristics were observed above the certain value of Hz > 3000 A/m. We consider the shift of the measured Ic-H dependence in the Hz minus direction occurred because of the flux quanta were trapped in the sample superconducting niobium film after the Hz value had been added greater than 3000 A/m.     

Magnetic stress anisotropy field in plated cylindrical permalloy films

An analysis is made of the magnetic stress anisotropy field Hks, arising from internal and external stress sources in plated-wire memory elements. The analysis takes into consideration circumferential composition variation and cylindrical geometry of the Permalloy film. Expressions are derived relating Hksto uniaxial film stress, average composition, and amplitude of composition variation. A result of particular importance is that even for average zeromagnetostrictive composition (ZMC) films, Hksmay still make an appreciable contribution to the total anisotropy field if the composition is not uniform. Calculated Hkscharacteristics are shown to correlate with anisotropy field changes observed in annealing experiments. Examples are given to show the importance of composition uniformity in determining the stability of the anisotropy field. The utility of the analysis is extended by the inclusion of data expressing the inverse relation between anisotropy field and easy-axis dispersion in the film.