Magnetoelectric-Field Electrodynamics: Search for Magnetoelectric Point Scatterers

Resonant scattering of electromagnetic (EM) waves by small particles is considered as one of the basic problems in metamaterial science. At present, special subwavelength resonators are considered as structural elements in chiral and bianisotropic metamaterials. There is a general consensus that these small scatterers behave like “artificial atoms” with strong electrical and magnetic responses and an interconnection between these responses. However, the observed effect of magnetoelectric (ME) coupling in these meta-atoms is not associated with the near-field manipulation properties caused by intrinsic magnetoelectricity. This arises the question whether ME point scatterers of EM radiation really exist. In this paper, we show that there are mesoscopic structures with electric and magnetic dipole-carrying excitations that behave like point scatterers with their inherent magnetoelectricity. In such subwavelength resonators, coherent oscillations of the electric polarization and magnetization can be considered as quasistatic oscillations described by electrostatic (ES) and magnetostatic (MS) scalar wave functions. The ME resonance effect arises from the coupling of two, ES and MS, oscillations. The near fields of these resonators, called the ME near fields, are characterized by simultaneous violation of time reversal and inversion symmetry. In study of ME fields and EM problems associated with these fields, we put forward the concept of ME-field electrodynamics.     

磁电异质结及器件应用

磁电异质结是由铁磁和铁电材料通过连接层耦合而成,其磁电效应来源于铁电相的压电效应和铁磁相的磁致伸缩效应.相对于颗粒混相磁电复合材料,层状磁电异质结材料具有更高的磁电耦合系数和更低的介电损耗,使得其在磁场传感器、能量收集器、天线以及存储器等领域都有着巨大的应用前景.本综述重点总结了磁电异质结材料的发展历程以及相关应用领域的最新进展,最后评述了磁电异质结材料发展的挑战和前景展望.     

磁致伸缩/压电层叠复合材料磁电效应分析

采用有限元分析软件COMSOL5.0建立了三维悬臂梁模型,分析了磁致伸缩/压电/磁致伸缩叠层复合材料的磁电系数α_(ME),并就几何参数对复合结构磁电系数的影响进行了优化分析.首先,利用稳态求解器研究了磁电层状复合结构内部的应力、应变、位移以及电势分布情况,利用瞬态求解分析了磁电复合结构各变量动态分布规律;其次,应用小信号频域分析研究了该结构的谐振频率以及在不同偏置磁场对输出电压的影响,结果表明,随着直流偏置磁场的增加,输出电压逐渐减小.改变复合材料不同层的厚度,分析了磁电层与压电层厚度比t_m/t_p对磁电系数的影响,结果表明,随着厚度比增加,α_(ME)逐渐增大,其增加速率逐渐减小;最后,分析了磁电系数α_(ME)随复合结构面积、长宽比的变化情况.分析表明,α_(ME)随磁电复合结构面积的增加逐渐增加,其增加速率逐渐减小;当磁电复合结构面积恒定时,其磁电系数随长宽比L/W增加表现出先增加后减小的趋势,存在最优值.     

磁电薄膜与微波作用研究

建立了双层磁电复合薄膜模型,当磁电材料尺寸可以与微波波长相比拟时,微波在传播方向上的偏导不为零,得到了微波与磁电材料作用的非齐次偏微分方程,并在谐振条件下对该方程进行了解析求解.推导出磁电系数和材料等效电学参数的解析表达式,结果表明磁电材料的磁电系数多出相关的耦合项,其大小不但与材料本身参数有关,还与微波在材料中的波速有关;等效导纳多出的耦合项与微波的频率有关.     

Comparison of Diffraction Fields of Lens by Two Calculation Formulas

Diffraction fields in the focal space of some lens is investigated by using ray tracing and Stratton-Chu formulas. Two formulas are used. One is surface integration formula, and for another a line integration is added. Comparison of two calculation results is given. It is shown that for hyperbolic lens two calculations results are same and for extended hemi-ellipsoidal lens there are a lilt difference between them.     

Optics of magnetoelectric media in the presence of a magnetic field and a spatial dispersion of the dielectric permittivity

Influence of an external magnetic field and a spatial dispersion of the dielectric permittivity on the irreversibility of waves in magnetoelectric media is considered. Features of the azimuth inhomogeneity at the simultaneous anisotropy of the dielectric permittivity and magnetic permeability in these media are studied.     

Magnetoelectric Energy in Electrodynamics: Magnetoelectricity,Bi(an)isotropy,and Magnetoelectric Meta-Atoms

Magnetoelectricity denotes the relationship between electric polarization and magnetization. In materials with an intrinsic magnetoelectric (ME) effect, the energy density comprises the polarization, magnetization, and ME energy densities. These three components of energy define local (subwavelength) characteristics of electromagnetic (EM) responses in multiferroic materials. In a subwavelength domain, coupling between the electric and magnetic dipole oscillations forms the ME field structures that are characterized by the violation of both spatial and temporal symmetry. Unlike multiferroics, bi(an)isotropic metamaterials are associated with an EM response characterized only by spatial symmetry breaking. This also applies to chiral materials. Since no “intrinsic magnetoelectricity” is assumed in such structures, any concepts about the stored ME energy are not applicable. This clearly points to the effect of nonlocality. That is why the basic concepts of bi(an)isotropy can only be analyzed by the EM far-field characteristics. In this paper, it is argued that in the implementation of local (subwavelength) ME meta-atoms and systems for near-field probing of chirality, the concept on ME energy is crucial. Real ME energy can occur when ME fields in a singular subwavelength domain are characterized by a violation of both the symmetry of time reversal and spatial reflection.     

Superposition of Stationary Wave Fields Via Atom Microscopy

We investigate one-dimensional position microscopy of a three-level atom moving through a stationary wave region under the condition of electromagnetically induced transparency.The precise position information of an atom is observed on the resonance absorption and dispersion distribution spectrum of a weak probe field.Single and multiple localization peaks are observed in specific directions of the corresponding wave numbers and phase of the standing wave fields.The strength of space-independent Rabi frequency reduces the position uncertainty in the localized peaks without disturbing the probability of the atom.In a hot atomic medium the localized probability of an atom is reduced which depends upon the temperature of that medium.Our results provide useful applications in the development of laser cooling,atom nanolithography and Bose-Einstein condensation.     

准2-2型磁电多层复合材料的磁电性能

用带底座的Pb（Zr,Ti）O₃薄片阵列作为压电相,Terfenol-D粉末与树脂的混合物作为磁致伸缩相,灌注复合得到准2-2型磁电多层三相复合材料.研究了这种准2-2型多层结构在不同偏置磁场和不同角度下的磁电效应.其面内相互垂直的两个方向磁电电压系数分别在0.15和0.225 T磁场下达到峰值,低频下分别为1.62×10⁵ V·m^-1T^-1和1.75×10⁵ V·m^-1T^-1;而在垂直于面内方向,低频下磁电系数仅有1.3×10⁴ V·m^-1T^-1,体现出显著的磁电各向异性.这种准2-2型磁电多层复合材料具有较好的交流磁场灵敏度,在谐振频率下可以探测到10^-9 T的交流磁场的变化.进行合适的设计和排列,可以探测空间磁场的大小和方向,有望应用于磁场传感器等领域. 关键词： 磁电效应 多铁性 多层复合材料     

复合多铁链的磁电耦合行为与外场调控

对含有界面磁电耦合的有限长铁电-铁磁多铁链体系进行了研究,基于矢量离散化思想,构建了描述其磁电性质的微观海森伯模型.利用传递矩阵方法获得了磁化强度、电极化强度、磁电化率等关键热力学量的解析表达式,重点探讨了界面磁电耦合、外场以及单离子各向异性对体系磁电耦合行为的影响和调控.研究结果表明,界面磁电耦合对体系的磁化强度和电极化强度均起促进作用.电场驱动下的电致磁电化率具有更强的磁电关联效应,预示着外电场能够有效地调控体系的磁性行为.而在磁致磁电化率中观察到的低温峰主要源于外磁场的诱导.此外,在高电场作用下体系比热容还呈现出有趣的三峰结构,这种三峰结构是自旋态的热激发以及电偶极矩的电场和温度共同激发导致的.     

TbDyFe/PZT层状复合材料的磁电效应研究

磁致伸缩/压电复合材料通过磁致伸缩和压电效应的乘积而可以获得大的磁电效应.用磁控溅射方法制备了TbDyFe/PZT层状复合材料，实验测试了TbDyFe/PZT两层及TbDyFe/PZT/TbDyFe三层复合材料的磁电电压系数随周期磁场频率的变化关系，并采用有限元数值计算方法对两种材料的磁电电压系数进行了计算.研究结果表明，实验测试曲线与数值计算结果符合很好，所制备的层状复合材料在共振频率处存在最大的磁电电压系数值，由于两层板与三层板的振动模式不同，三层复合板的共振频率远高于两层复合板的共振频率.在非共振频率下，三层复合板的磁电转换效应高于两层复合板.有限元计算结果还显示，磁电层状复合材料的磁电电压系数随磁致伸缩层厚度的增加而增大. 关键词： 磁电效应 层合板 TbDyFe 有限元分析     

单相ABO3型多铁材料的磁电耦合及磁电性质研究

实验发现多铁性钙钛矿物质YMnO₃和BiMnO₃在接近磁有序相变温度时,其介电常数和正切损失会出现异常,这些现象说明在物质的磁性和介电性质之间存在耦合.通过对系统磁性和铁电性之间可能磁电耦合方式的分析,考虑在系统哈密顿量中加入与自旋关联和极化相关的耦合项,对铁电子系统应用软模理论,对磁性运用基于海森伯模型的量子平均场近似,研究了外磁场诱导的极化、介电的变化和外电场诱导的磁化的变化等,并将以上结果与实验进行了比较和分析,较为合理地解释了一些多铁钙钛矿物质中的磁电现 关键词： 多铁 磁电耦合 铁电 铁磁     

Numerical Analysis of Electromagnetic Fields in Multiscale Model

Modeling technique for electromagnetic fields excited by antennas is an important topic in computational electromagnetics, which is concerned with the numerical solution of Maxwell's equations. In this paper, a novel hybrid technique that combines method of moments(MoM) with finite-difference time-domain(FDTD) method is presented to handle the problem. This approach employed Huygen's principle to realize the hybridization of the two classical numerical algorithms. For wideband electromagnetic data, the interpolation scheme is used in the MoM based on the dyadic Green's function. On the other hand, with the help of equivalence principle, the scattered electric and magnetic fields on the Huygen's surface calculated by MoM are taken as the sources for FDTD. Therefore, the electromagnetic fields in the environment can be obtained by employing finite-difference time-domain method. Finally, numerical results show the validity of the proposed technique by analyzing two canonical samples.     

电磁波在多层介质内的透射

导了多层介质中透射电磁波的电场振幅与介质表面入射电磁波场电场振幅之间的关系式，引入了一个母函数，通过微分可以生成介质各层中的透射波。     

Quantum effects of nonlinear spin waves in ferromagnets

We investigate a squeezed thermal spin state of nonlinear spin waves in Heisenberg ferromagnets. In this state, the magnon system possesses a new kind of quasiparticle, the dressed magnon, whose mass is a monotonically decreasing function of temperature. The noise of one spin component in the squeezed thermal spin state can be below the noise level in the vacuum state. The magnon system undergoes a first-order phase transition from the normal state to the squeezed thermal spin state. The critical temperature is much lower than the Curie temperature. A possible detection scheme based on a polarized neutron-scattering technique is suggested.     

应变作用下量子顺电材料EuTiO3的磁电性质

由于磁性和介电性质的强烈耦合, 量子顺电材料EuTiO₃材料的研究近来倍受人们的关注. 本文通过运用基于密度泛函理论的第一性原理计算研究了量子顺电(PE) 材料EuTiO₃的磁性和电子结构, 分析了应变对磁性和结构相变的作用, 从而探讨了该材料中可能的磁电耦合机理. 结果发现, 在无应变状态下, EuTiO₃处于顺电立方-G型反铁磁性态, 而对于c轴方向的无论张应变还是压应变, 当应变增加到一定程度时, 由于Ti 3d空轨道与周围O 2p 电子的杂化平衡被打破, EuTiO₃将相变到铁电( FE) 四方-铁磁结构, 显示了强烈的自旋-晶格耦合效应.     

Magnetic Field‐Controlled Release of Paclitaxel Drug from Functionalized Magnetoelectric Nanoparticles

Using magnetoelectric nanoparticles (MENs) for targeted drug delivery and on‐demand, field‐controlled release can overcome the control challenges of the conventional delivery approaches. The magnetoelectric effect provides a new way to use an external magnetic field to remotely control the intrinsic electric fields that govern the binding forces between the functionalized surface of the MEN and the drug load. Here, a study is reported in which the composition of the intermediate functionalized layer is tailored to control not only the toxicity of the new nanoparticles but also the threshold magnetic field for the dissociation of the drug from 30‐nm CoFe₂O₄–BaTiO₃ core–shell MENs in a controllably wide field range, from below 10 to over 200 Oe, as required to facilitate superficial, intermediate, and deep‐tissue drug delivery. Paclitaxel is used as a test drug. Specific experiments are described to maintain low toxicity levels and to achieve controllable dissociation of the drug molecules from the MENs' surface at three different subranges—low (<10 Oe), moderate (100 Oe), and high (>200 Oe)—by selecting the following 2‐nm intermediate layers: i) glycerol monooleate (GMO), ii) Tween‐20, and iii) ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC). Field‐dependent FTIR, absorption spectra, atomic force microscopy, magnetometry analysis, zeta‐potential measurements, and blood circulation experiments are used to study the described functionalization effects.     

极化电场对可激发介质中螺旋波的控制

螺旋波在不同的物理、化学和生物系统中普遍存在.周期外场,比如极化电场,尤其是具有旋转对称性的圆极化电场可对螺旋波动力学产生重要影响.本文综述了极化电场对可激发介质中螺旋波的控制,包括共振漂移、同步、手征对称性破缺、多臂螺旋波的稳定、次激发介质中的螺旋波、三维回卷波湍流态的控制、心脏组织中螺旋波的去钉扎、心脏组织中螺旋波湍流态的控制等.     

Longitudinal Optical Fields in Light Scattering from Dielectric Spheres and Anderson Localization of Light

Recent research has shown that coupling between point scatterers in a disordered medium by longitudinal electromagnetic fields is harmful for Anderson localization of light. However, it has been unclear if this feature is generic or specific for point scatterers. The present work demonstrates that the intensity of longitudinal field outside a spherical dielectric scatterer illuminated by monochromatic light exhibits a complicated, nonmonotonous dependence on the scatterer size. Moreover, the intensity is reduced for a hollow sphere, whereas one can adjust the parameters of a coated sphere to obtain a relatively low longitudinal field together with a strong resonant scattering efficiency. Therefore, random arrangements of structured (hollow or coated) spheres may be promising three‐dimensional disordered materials for reaching Anderson localization of light.