磁性多孔纳米片微波磁导率的微磁学研究

本文基于微磁学理论模拟了多孔α-Fe纳米片的微波磁性能. 与无纳米孔洞的纳米片对比, 发现由于纳米孔洞的引入导致退磁能发生改变, 破坏了纳米片原有的磁畴分布, 使纳米片内部存在数目更多、体积更小、局域有效场强不同的磁畴, 从而增加了高频磁损耗峰的数目. 由于部分损耗峰的相互交叠, 为在10–30 GHz范围拓宽电磁波吸收的带宽提供了潜在可能性. 模拟结果表明多孔纳米片的磁损耗峰数目、强度、峰宽和频率分布受孔洞排布方式和孔洞数目的影响. 由于纳米孔洞的存在可以降低材料的密度, 模拟结果表明多孔α-Fe纳米片可用于开发吸收频段宽、重量轻的电磁波吸收材料.     

FEM analysis of magnetic flake composites

A composite comprised of layered flake-like magnetic particles embedded in an insulating medium has been proposed as a low permeability, low loss core material. This would be an alternative to “distributed air gap” compressed powder cores that are widely used for inductors in power applications. Since the lowest loss metallic materials are manufactured in the form of very thin sheets, the particles after pulverizing would be in the form of flakes. The effective permeability and average core loss have been computed for model systems of flake composites in a two-dimensional approximation. The core loss is modeled by eddy current dissipation in the low-frequency limit, where the conductor thickness is much less than the skin depth. It is found that useful values of permeability should be obtained for a modest filling fraction of magnetic material, in contrast to the powder cores which require a value close to unity. The core loss will scale as the inverse of filling fraction, with a small additional enhancement due to perpendicular field components. It is thus expected that useful core materials may be attainable without the necessity of large compaction forces.     

Vector magnetisation measurements on thermally evaporated CoCr multilayers and solid solutions for spintronic applications

Structure, morphology and magnetic properties of thermally evaporated Co/Cr multilayers and of the solid solution obtained by isothermal treatment of the layered samples have been studied to evaluate their potential application as high-coercivity materials for hard spin injectors in spintronic devices such as magnetic tunneling junctions. The thermal treatment was performed in a partial pressure of inert gas to allow interdiffusion of Cr and Co. Structure and composition of the materials, as well as the effects of the annealing treatment, have been investigated by field emission scanning electron microscopy and energy-dispersive X-ray analysis. The magnetic configuration of these films was investigated by magnetic force microscopy. Simultaneous measurements of two mutually perpendicular magnetisation components were performed by means of a vector vibrating sample magnetometer, and showed that the in-plane coercivity can be increased by proper thermal treatment from less than 10 Oe to about 240 Oe. However, annealing may result in a loss of compositional and morphologic homogeneity of the films.     

空间高频交变磁场对超导块材悬浮力影响研究

高温超导磁悬浮装置,如磁悬浮列车和磁悬浮轴承在高速运行时,空间磁场交变及不均匀性扰动会引发超导块材内部损耗并影响性能,传统均匀时变磁场实验研究及仿真模拟无法满足实际工程应用情况.本文通过设计不同永磁阵列得到不同波形,在高速系统驱动下得到不同交变频率下超导块材损耗特性,发现全波型损耗较半波型损耗高,并研究了不同磁场构型悬浮力衰减特性,可为高速超导磁浮应用提供实验依据.     

固态脉冲功率驱动源主磁开关的特性

为了提高固态脉冲功率驱动源的工作性能,研究了使用磁开关作为主开关的关键参数。分析了磁芯体积、磁芯损耗以及饱和电感等关键参量对磁开关工作性能的影响。结果表明:对于选用的磁开关,当磁性高度为0.05 m时,磁开关的封装系数取得极大值;平均磁路长度大于1 m时,磁芯绕组的饱和电感变化缓慢。利用饱和波理论简要解释了磁芯饱和的物理过程,推导了磁开关输出脉冲上升时间因子表达式,结果表明:磁性材料厚度、电阻率以及磁芯内外层磁路长度差等参数是影响磁开关输出脉冲上升因子的重要因素。     

磁性材料进展

磁性材料大体上分为两类 :其一为铁磁有序的金属磁性材料 ;其二绝大多数为亚铁磁有序、具有半导体导电性质的非金属磁性材料 .5 0年代以前 ,金属磁性材料占绝对优势 ;5 0年代以后 ,非金属磁性材料发展成为磁性材料的主流 ,除电力工业用的高饱和磁化强度FeSi合金外 ,铁氧体几乎应用于各个领域 .历史似乎按螺旋形的方式发展 ,90年代后 ,金属磁性材料又以新的面貌出现 ,3d (4f,4d ,5d ,5f… )合金与化合物、非晶、纳米微晶磁性材料重领风骚 ,其性能远超越铁氧体 .纳米磁性材料将成为新的功能材料 .文章重点介绍了永磁材料与软磁材料 ,其他如磁记录材料、磁致冷材料、磁致伸缩材料等将作简单介绍 .     

Analysis of the role of M-type hexaferrite-based materials in electromagnetic interference shielding

M-type hexaferrite has attracted much attention for its large magneto-crystalline anisotropic energy, exceptionally good chemical stability, corrosion resistance, high Curie temperature, and high coercivity. In this review paper, our goal is to examine the microwave absorption properties and related studies of M-type hexaferrite-based materials. The microwave absorption properties of hexaferrite-based materials in the S, X, and Ku-band are discussed with their corresponding reflection losses. Complementarity between magnetic loss and dielectric loss is found to have a great impact on the proper absorption of microwaves. The mechanisms corresponding to the microwave absorption in different morphologies and structural adaptations of hexaferrite have been elaborated in the article. The ongoing trends and future perspectives of these materials are also outlined.     

磁性材料新近进展

磁性材料是应用广泛、品种繁多的一类重要的功能材料，20世纪90年代以后发展十分迅速．稀土-3d过渡族磁性合金材料，如稀土水磁、巨磁致收缩材料、巨磁热效应材料，磁光效应材料等，以及非晶，纳米微晶磁性材料相继问世．1988年巨磁电阻效应的发现已获广泛应用，如读出磁头、传感器以及磁随机存储器等，并发展成为自旋电子学的新学科．文章简要介绍了近年来磁性材料的一些新进展。     

Magnetorheological and deformation properties of magnetically controlled elastomers with hard magnetic filler

Viscoelastic and deformational behavior of soft magnetic elastomers with hard magnetic fillers under the influence of a magnetic field is studied by different experimental techniques. The magnetic elastomers used in this work were synthesized on the basis of silicone rubber filled with FeNdB particles and were magnetized in a field of 3 and 15 kOe. We have shown that due to high residual magnetization the materials demonstrate well pronounced non-elastic behavior already in the absence of any external magnetic field. In particular, in contrast to magnetic elastomers based on soft magnetic fillers their elastic modulus is strain-dependent. Under the influence of external magnetic field the storage and loss moduli of magnetic elastomers with hard magnetic filler can both increase and decrease tremendously.     

基于磁光子晶体的低损耗窄带THz滤波器

本文提出一种采用石榴石型铁氧体磁性材料的太赫兹滤波器,利用波导线缺陷和腔内点缺陷的耦合特性,通过改变腔内介质柱半径及分布,实现对某个波长的耦合,达到了高效率滤波的功能;改变外磁场的大小,影响铁氧体材料的磁导率变化,使谐振频率发生改变,从而对THz波进行滤波.应用平面波展开法(PWM)和时域差分有限法(FDTD)进行仿真分析,研究结果表明,该滤波器其插入损耗为0.0997 d B,3 d B带宽为8.22 GHz,实现了低损耗窄带滤波.     

A novel technique for measurement of core loss in low permeability materials

A survey of existing techniques for measuring core loss in magnetic materials is presented. It is shown that the most challenging combination is a low permeability material at low measurement frequency. Such materials have application in components of power converters, and thus are of considerable technological significance. Measurement difficulties stem from losses in the windings employed, which are difficult to disentangle from loss in the core, as well as the stringent requirements on phase accuracy of measurement instruments. Another practical problem is the large power capacity required of the drive source to achieve significant induction levels. A new resonant measurement setup, which we call the “virtual impedance” technique, is proposed as a solution to these problems. Its utility is demonstrated with measurements of a commercial composite core with permeability 14μ₀ whose low-core loss defeats conventional methods of measurement.     

一种铁基超导带材交流损耗的测量

近年来铁基超导材料的发现掀起了又一轮新型超导材料研究的热潮,各种配方的铁基超导材料不断被制备出来,转变温度也不断提高,中国科学家在该领域取得了十分突出的成果,制备出了多种铁基超导材料,但对其交流损耗特性研究鲜有报道,而实际应用中交流损耗的特性又十分重要,因此搭建了一套采用探测线圈法的交流损耗测量平台,测试了一种中国科学院电工研究所采用PIT工艺制作的单芯铁基超导带材的交流损耗。该文介绍了采用探测线圈法测量超导材料交流损耗的一种测量平台的搭建与标定,以及采用标定过的测量平台在液氦温度下测量的一种采用PIT工艺制作的单芯铁基超导带材的交流损耗;并与计算得到的铁基带材超导芯的磁滞损耗和包套的涡流损耗进行了比较分析,得出了其交流损耗与背景磁场频率成正比,其涡流损耗可以忽略的结论。     

Microwave-absorbing properties of shape-optimized carbonyl iron particles with maximum microwave permeability

The microwave-absorbing properties for different shapes of carbonyl-iron particles prepared by the high-energy planetary ball milling with 40 vol% in epoxy resin matrix have been investigated. Higher value of magnetic permeability and permittivity can be obtained in the composites for thin flake carbonyl iron than spherical powders. The results are attributed to reduction of eddy current loss, orientation of magnetic moment and space-charge polarization with the shape change from spherical powders to thin flake particles. As the iron flakes with 0.4 μm in thickness as the absorbent fillers, the minimum RL value of −6.20 dB was observed at 4.57 GHz with thickness of 1 mm. The minimum reflection loss (RL) shifts to lower frequency and the value declines with change from spherical powders to thin flakes. It results from the considerable dielectric loss in the absorbing materials.     

Connection between microstructure and magnetic properties of soft magnetic materials

The magnetic behavior of soft magnetic materials is discussed with some emphasis on the connection between macroscopic properties and underlying micromagnetic energy aspects. It is shown that important conceptual gaps still exist in the interpretation of macroscopic magnetic properties in terms of the micromagnetic formulation. Different aspects of hysteresis modeling, power loss prediction and magnetic non-destructive evaluation are discussed in this perspective.     

非晶态物理与软磁材料的产业化

由于非晶态材料具有独特的结构和优异的性能，其发现和发展对相关传统材料及其应用领域产生了巨大的冲击和深远的影响。从1960年首次发现非晶合金至今已有40余年，基础研究和应用开发均取得长足进展，特别是作为软磁材料的非晶合金带材已经实现了产业化，并获得了广泛应用。文章综述了非晶态物理方面的一些基本问题，以及非晶办磁合金的发展历史和产业化现状。     

Synthesis and characterization of cobalt–manganese oxides

Cobalt doped/un-doped manganese oxides materials were synthesized at various doping rates by soft chemical reactions, oxidation-reduction method, which allows generating a metal-mixed oxide. The synthesized materials were characterized using several techniques including chemical analysis, X-rays diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The chemical analysis confirmed the presence of cobalt in the samples. XRD patterns reveal mainly a spinel-like structure and SEM micrographs exhibited morphology with fine aggregate of particles. TGA profiles showed weight loss due to loss of water in a first step, followed by a loss of oxygen from the lattice associated with partial reduction of Mn⁴⁺ to Mn³⁺. VSM was used to measure the magnetization as a function of the applied magnetic field at temperatures T=50 and 300 K. Different magnetic behaviors were observed when cobalt percentage changed in the samples. These behaviors are considered to be related to the size of the particles and composition of the materials. Higher coercive field and lesser magnetization were observed for the sample with higher cobalt content.     

A Highly Tunable Silicone-Based Magnetic Elastomer with Nanoscale Homogeneity

Magnetic elastomers have been widely pursued for sensing and actuation applications. Silicone-based magnetic elastomers have a number of advantages over other materials such as hydrogels, but aggregation of magnetic nanoparticles within silicones is difficult to prevent. Aggregation inherently limits the minimum size of fabricated structures and leads to non-uniform response from structure to structure. We have developed a novel material that is a complex of a silicone polymer (polydimethylsiloxane-co-aminopropylmethylsiloxane) adsorbed onto the surface of magnetite (γ-Fe₂O₃) nanoparticles 7-10 nm in diameter. The material is homogenous at very small length scales (<100 nm) and can be crosslinked to form a flexible magnetic material, which is ideally suited for the fabrication of micro- to nanoscale magnetic actuators. The loading fraction of magnetic nanoparticles in the composite can be varied smoothly from 0 to 50 wt% without loss of homogeneity, providing a simple mechanism for tuning actuator response. We evaluate the material properties of the composite across a range of nanoparticle loading, and demonstrate a magnetic-field-induced increase in compressive modulus as high as 300%. Furthermore, we implement a strategy for predicting the optimal nanoparticle loading for magnetic actuation applications, and show that our predictions correlate well with experimental findings.     

Magnetic properties of the ferrimagnetic glass-ceramics for hyperthermia

Magnetic materials play a key-role in magnetic induction hyperthermia for the treatment of cancer. In this paper, we analyse the magnetic properties of ferrimagnetic glass-ceramics with the composition in the system SiO₂–Na₂O–CaO–P₂O₅–FeO–Fe₂O₃, as a function of the melting temperature. These materials were obtained by melting of commercial reagents in the temperature range of 1400–1550 °C. Room-temperature magnetic measurements were performed by means of a vibrating sample magnetometer at room temperature. The power loss was determined from calorimetric measurements, using a magnetic induction furnace. The highest power loss (61 W/g) has been obtained for samples melted at 1500 °C. The heat generation of the ferrimagnetic glass-ceramics prepared by two different synthesis methods (traditional melting and coprecipitation-derived) will be compared. These materials are expected to be useful in the localised treatment of cancer.     

Magnetic van der Waals materials: Synthesis,structure, magnetism,and their potential applications

As the family of magnetic materials is rapidly growing, two-dimensional (2D) van der Waals (vdW) magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their potential applications. This paper reviews the recent progress on emergent vdW magnetic compounds and their potential applications in devices. First, we summarize the current vdW magnetic materials and their synthetic methods. Then, we focus on their structure and the modulation of magnetic properties by analyzing the representative vdW magnetic materials with different magnetic structures. In addition, we pay attention to the heterostructures of vdW magnetic materials, which are expected to produce revolutionary applications of magnetism-related devices. To motivate the researchers in this area, we finally provide the challenges and outlook on 2D vdW magnetism.     

Tailoring magnetism in artificially structured materials: the new frontier

The current standard of electronic devices and data storage media has reached a level such that magnetic materials have to be fabricated on a nanometer scale. In particular, the emerging concept of spintronics, which is based on fact that current carriers have not only charge but also spin, requires the assembling of nanometer-sized magnetic structures with desired magnetic properties. It is this background that motivates scientists and engineers to attempt to grow and characterize magnetic objects at smaller and smaller length scales, from 2D films and multilayers to 1D wires and eventually to 0D dots. In this article, some of the most significant progress in recent years in the effort of growing artificially structured magnetic materials are reviewed. The new structural and magnetic properties of these materials are discussed, with an emphasis on the correlation between structure and magnetism, which also serves as guidance for improving their magnetic properties. The emerging emphasis is on converting the existing knowledge into growing and studying low-dimensional complex materials, which promise to have considerably higher “tuning” ability for desired properties.