铌酸钾钠/铁酸钴铜多铁性磁电复合材料的制备及性能研究

通过固相法制备了(1–x)(0.9462K0.5Na0.5NbO3-0.0498LiSbO3-0.004BiFeO3)-xCo0.85Cu0.15Fe2O4((1–x)(KNN-LS-BFO)-xCCFO)(x=0.1、0.2、0.3、0.4、0.5)复合多铁性磁电陶瓷.XRD分析表明:烧结后的样品为复合的钙钛矿和尖晶石结构,没有发现杂相产生.SEM照片显示KNN-LS-BFO晶粒生长完好尺寸较大,而CCFO晶粒尺寸较小.当x从0.1增加到0.5时,复合材料的压电系数从120 pC/N减小到33 pC/N,而饱和磁化强度和剩磁增加,饱和磁致伸缩系数从18×10–6增加到51.5×10–6左右.材料的磁电耦合系数随着外磁场的增加先增大到极大值后再减小;当交变磁场频率为1 kHz,x=0.3时材料的磁电电压系数达到最大值20.6 mV/A.     

磁电复合材料的制备及研究进展

综述了磁电复合材料的合成工艺和研究现状.磁电复合的基本理论是基于乘积效应的,指出了获得高磁电效应的基本条件.分别详述了包括颗粒复合、粘合层状复合以及纳米复合在内的3种不同复合方式磁电复合材料的制备工艺,讨论了这些磁电复合材料制备方法的优缺点,并对磁电复合材料制备这一研究领域进行了展望.     

Azimuthally unidirectional transport of energy in magnetoelectric fields: topological Lenz’s effect

Magnetic-dipolar modes (MDMs) in a quasi-2D ferrite disc are microwave energy-eigenstate oscillations with topologically distinct structures of rotating fields and unidirectional power-flow circulations. At the first glance, this might seem to violate the law of conservation of an angular momentum, since the microwave structure with an embedded ferrite sample is mechanically fixed. However, an angular momentum is seen to be conserved if topological properties of electromagnetic fields in the entire microwave structure are taken into account. In this paper, we show that due to the topological action of the azimuthally unidirectional transport of energy in a MDM-resonance ferrite sample there exists the opposite topological reaction on a metal screen placed near this sample. We call this effect topological Lenz’s effect. The topological Lenz’s law is applied to opposite topological charges: one in a ferrite sample and another on a metal screen. The MDM-originated near fields – the magnetoelectric (ME) fields – induce helical surface electric currents and effective charges on a metal. The fields formed by these currents and charges will oppose their cause.     

铁电-铁磁复合材料的研究现状及发展趋势

铁电—铁磁复合材料是一种由铁电相和铁磁相复合而成，具有磁电转换功能的新材料，它兵有广阔的应用前景。系统地介绍了铁电—铁域复合材料的原理、性质及研究进展，最后对存在的问题及发展趋势作了分析。     

PbTiO_3-CoFe_2O_4磁电复合材料的结构和电性能

采用传统固相烧结法制备不同组分的PbTiO3-CoFe2O4磁电复合材料,采用X射线衍射(XRD)和扫描电子显微镜(SEM)等手段进行分析表征。结果表明:PbTiO3-CoFe2O4复合材料的复合形式为0-3型。1 100℃烧结的PbTiO3-CoFe2O4复合材料具有良好的相结构,同时具有明显的铁电性和铁磁性。PbTiO3-CoFe2O4复合材料的磁性能呈现规律的变化,介电常数却由于元素扩散和铁磁相的约束及稀释作用等原因产生了异常的变化。     

多重铁性材料的研究进展

多重铁性材料是一类可以同时具有(反)铁电、(反)铁磁及铁弹中两者或两者以上耦合性质的多功能材料,其丰富的物理现象和颇大的应用潜力受到学术和工程领域的广泛关注.归纳了多重铁性材料的研究进展,包括种类、耦合机理、制备方法和影响因素等;讨论了其实验和理论研究中的发展及存在的问题,并在此基础上展望了多重铁性材料的研究前景.     

Magnetoelectric Spin-FET for Memory,Logic, and Amplifier Applications

We propose a ballistic magneto-electric device that permits conductance modulation with both electric and magnetic fields applied perpendicular to its current conduction channel. Fields are applied through the ferromagnetic gates deposited on top of a HEMT heterostructure that contains a 2DEG for current conduction. The minimal-coupling Hamiltonian with spatially uniform electrical potentials, and delta Zeeman splitting is solved in the weak-coupling limit for which the Rashba spin orbit coupling is not considered. Ballistic transmission of electrons through a periodic system of zero-gauge double-pair magnetoelectric barriers is studied. Manipulation of barriers’ geometrical symmetry and configuration leads to the conception of a spin-FET for non-volatile storage and digital logic operations. The linear modulation of electron spin polarization (|P|) is also studied for its relevance to electrical signal amplification. Perpendicular magnetization of the ferromagnetic gates permits modulation of both |P| and electron transmission (T) threshold, the latter is particularly useful for spin logic design.     

CaCu3Ti4O12/NiCuZn铁氧体基磁电复合材料研究

将CCTO(CaCu3Ti4O12)与NiCuZn铁氧体进行复合,系统地研究了组分变化对这种新型磁电复合材料的烧结性能、晶相结构、显微结构和磁电性能的影响。随后,为了实现复合材料的低温烧结以及综合考虑复相陶瓷的磁电性能,选取80%(质量分数,下同)NiCuZn铁氧体/20%CCTO组分,以BBSZ(Bi2O3-H3BO3-SiO2-ZnO)玻璃作为助熔剂,研究了CCTO/NiCuZn铁氧体基复合材料的烧结行为和磁电性能。结果表明,掺杂BBSZ后,900℃下烧结的所有样品的密度均达到了复相陶瓷理论密度的95%,且复相陶瓷的介电常数和磁导率在1～30 MHz范围内均不依赖于频率的变化。在10 MHz的频率下,当BBSZ的含量从0增加到3%时,复相陶瓷磁导率μ从13.2增加到47.9,磁损耗tanδμ从0.022下降到0.017,同时,样品的谐振频率从109Hz左右移动到3.2×108Hz。相应地,复相陶瓷的介电常数ε从9.2增加到16,介电损耗tanδε从0.069下降到0.012。这一优异的整体性能使其有望实际应用。     

层状复合材料磁电效应的数值分析

压电与压磁(或磁致伸缩)层合板具有大的乘积效应磁电效应。本文采用有限元分析方法对压电/压磁层合板的磁电转换进行了计算,结果表明:外磁场方向对磁电转换效应有很大的影响,在层合板上下两面增加约束可以大大提高层合板的磁电转化效应;感生电压值随压磁/压电板厚比的增加而增加,而整个层合板的电场强度值在板厚比为1时达到最大。     

FeGa/BTO/FeGa层状复合结构中的磁电效应

采用区域熔炼法制备了FeGa磁致伸缩材料并测量了其磁致伸缩性能.利用该材料制备了FeGa/BTO/FeGa层状复合结构,并对该样品的磁电性能进行了系统研究.结果表明,该材料在共振频率95kHz下,磁电性能高于低频下性能7～10倍.磁电电压随直流偏磁场的变化发生明显变化,出现5.97×104A/m的优化偏置场,这主要是由FeGa层的压磁系数q随偏磁场的变化所致.3层复合材料的磁电系数与交流驱动场变化呈线性关系.另外,较薄的BTO压电层可以提高压应力,从而获得较高的磁电性能.     

压电/磁致伸缩/环氧树脂层合复合材料的磁电效应及其频响特性

磁电复合材料在磁-电能量转换等领域具有重要的潜在应用价值, 研究磁电复合材料在较高频率下的磁电耦合特性对于实际应用具有重要意义。本文中以0-3型的Terfenol-D(Tb_0.30Dy_0.70Fe₂)/环氧树脂复合材料为磁致伸缩层, 以PZT 压电陶瓷为压电层, 制备了三明治结构的层合磁电复合材料。研究了Terfenol-D/环氧树脂复合材料层的磁致伸缩性质, 并对所制备的层合磁电复合材料磁通密度、 介电常数以及磁电电压系数等随频率和偏磁场的变化规律进行了系统研究。结果表明, 由于Terfenol-D/环氧树脂复合材料的引入, 层合磁电复合材料呈现出良好的频率响应特性, 可靠工作范围大大拓宽。层合磁电复合材料具有优良的动态磁电耦合性能, 在优化偏磁场630 Oe和共振频率69.6kHz下的磁电效应高达21.2 V/cmOe。此外, 层合磁电复合材料的磁电效应随偏磁场的变化发生明显变化, 并存在优化偏磁场。对上述现象和结果进行了详细讨论, 并给出了层合磁电复合材料的磁电耦合机制。      

Magnetic ferroelectric materials

In the form of a succinct overview the structure and symmetry requirements of magnetic ferroelectrics are discussed. Boracites are the best-studied examples and have phases being simultaneously ferroelectric, ferromagnetic and ferroelastic. One of the salient features of such materials is the obligatory occurrence of the linear and bilinear magnetoelectric effects. They represent an invaluable auxiliary information for magnetic symmetry determination by neutron diffraction. Owing to the complexity of property combinations, work with single crystals and polarized light microscopy is obligatory. Key references of the field are given.     

Multiferroic Heterostructures Integrating Ferroelectric and Magnetic Materials

Multiferroic heterostructures can be synthesized by integrating monolithic ferroelectric and magnetic materials, with interfacial coupling between electric polarization and magnetization, through the exchange of elastic, electric, and magnetic energy. Although the nature of the interfaces remains to be unraveled, such cross coupling can be utilized to manipulate the magnetization (or polarization) with an electric (or magnetic) field, known as a converse (or direct) magnetoelectric effect. It can be exploited to significantly improve the performance of or/and add new functionalities to many existing or emerging devices such as memory devices, tunable microwave devices, sensors, etc. The exciting technological potential, along with the rich physical phenomena at the interface, has sparked intensive research on multiferroic heterostructures for more than a decade. Here, we summarize the most recent progresses in the fundamental principles and potential applications of the interface‐based magnetoelectric effect in multiferroic heterostructures, and present our perspectives on some key issues that require further study in order to realize their practical device applications.     

离轴磁控溅射法生长1-3维PZT-NFO纳米复合薄膜

采用90°离轴磁控溅射法, 在MgAl₂O₄(001)单晶基片上自组装生长了Pb(Zr_0.52Ti_0.48)O₃-NiFe₂O₄ (PZT-NFO)复合磁电薄膜, 并研究了基片温度、氩氧比和溅射功率等因素对薄膜结构和性能的影响。结果表明, 适合生长PZT-NFO薄膜的条件为基片温度800℃, 氩氧比1:1, 溅射功率160 W。XRD测试显示, PZT-NFO薄膜为外延生长薄膜, 且PZT相与NFO相之间的垂直晶格失配非常小。AFM和SEM结构观察表明, 薄膜具有清晰的1-3维纳米复合结构, 铁磁相NFO纳米柱直径约为80~150 nm。降低氩氧比有助于NFO相的形成, 但溅射功率过大会造成1-3维结构向无规则0-3维结构转变。磁性能测量表明纳米复合薄膜的饱和磁化强度在120~160 kA/m之间, 低于块体的NFO相, 可能是由于两相的界面扩散所造成。     

Dielectric behaviour and magnetoelectric effect in cobalt ferrite-barium titanate composites

Composites of BaTiO₃ and CoFe₂O₄ have been prepared with various compositions by double sintering method. The presence of the two phases has been confirmed by XRD. Variation of dielectric constant with temperature in these samples has been studied. All the samples have shown linear magnetoelectric conversion in the presence of static magnetic field. The magnetoelectric effect (dE/dH) has been studied as a function of intensity of magnetic field. The maximum value of the conversion factor (dH/dH)_max was found to be 0·16 mV/cm/Oe.     

An experimental setup for dynamic measurement of magnetoelectric effect

An experimental setup is developed for the measurement of dynamic magnetoelectric effect (ME) in polycrystalline materials, using a time varying DC magnetic field on which an AC magnetic field is superimposed. The experimental data on ME on Bi₅FeTi₃O₁₅ and a solid solution of (90%)BiFeO₃-(10%)BaTiO₃ are obtained using this setup. The linear and higher order ME coefficients can be evaluated from the output voltage. The temperature variation of ME data gives additional information corroborating with the data on magnetization.     

Nonlocal effective parameters of a coated sphere medium

An analytical theory has been developed to find the general effective parameters of a nonlocal medium. The medium is nonlocal due to presence of spatial dispersion. The proposed theory is based upon the dipolar scattering model of the inclusions comprising the medium. The bianisotropy stemming from the magnetoelectric coupling at the inclusion and lattice level has been discussed. The developed theory is then applied to a medium which consists of coated spheres with realistic materials. Effects of different values of wavevector upon the effective permittivity, effective permeability, and magnetoelectric coefficient stemming from lattice effects have been studied for a coated sphere medium. It is shown that a coated sphere medium with a weak spatial dispersion gives rise to a broader range of frequencies, where real parts of the effective permittivity and permeability are negative. On the other hand, this range of frequencies becomes smaller when the spatial dispersion of the medium is not weak.     

单相多铁性磁电体磁电起源及耦合机理分析

单相多铁性磁电体是指在同一相下既有铁电性又有铁磁性的材料,其丰富的物理机制和极大的应用潜力近来受到国内外学术界和工程应用领域的广泛关注.电极化和磁化通过内禀的磁电耦合作用为下一代多功能电子器件的设计提供了额外的自由度.简单回顾了单相磁电材料研究的历史以及最新进展,从其导电性、对称性、化学d0性、结构畸变等方面详细讨论了单相多铁性磁电体磁电性的起源及耦合,并简单分析了磁电材料产业化进程中存在的问题,展望了多铁性磁电体的研究及应用前景.