Magnetoelectric laminate based DC magnetic field sensor

We report on a DC magnetic field sensor that utilizes magnetoelectric (ME) laminate composites. It consists of a ring‐dot piezoelectric transformer laminated to a magnetostrictive disc. When a constant voltage is applied to the ring section of the piezoelectric layer at resonance, a stress is induced in the dot section. Then, if an external magnetic object is introduced in the vicinity of the dot section, the effective elastic stiffness is increased, altering the resonance frequency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tb1-xDyxFe2-y-Fe掺杂BaTiO3多层膜中的磁电耦合

用溶胶-凝胶法制备了Fe掺杂BaTiO3粉体,在1350℃下烧结成圆片状多晶样品,并与Tb1-xDyxFe2-y胶合成磁电(ME)双层膜或三层膜.实验分析表明Fe:BaTiO3依然是四方相钙钛矿结构,但是居里温度及相变潜热均略低于纯净BaTiO3.研究了Tb1-xDyxFe2-y-Fe∶BaTiO3双层膜和Tb1-xDyxFe2-y-Fe∶BaTiO3-Tb1-xDyxFe2-y三层膜的ME效应.在2.8×104 A/m的磁场下,两者的横向ME电压系数均达其峰值,分别为6.225和26.25 mV·(A·m-1)-1·cm-1.并且,用掺杂BaTiO3制备的双层膜和三层膜的横向ME电压系数均为相同条件下用纯净BaTiO3制备的双层膜和三层膜的横向ME电压系数的1.5倍.另外由于不含铅,锆等有害物质,符合环保要求,因此采用掺杂BaTiO3制备的磁电效应器件具有深入研究和应用价值.     

Tb1－xDyxFe2－y-Fe掺杂BaTiO3多层膜中的磁电耦合

用溶胶-凝胶法制备了Fe掺杂BaTiO₃粉体，在1350℃下烧结成圆片状多晶样品，并与Tb_1-xDy_xFe_2-y胶合成磁电(ME)双层膜或三层膜.实验分析表明Fe：BaTiO₃依然是四方相钙钛矿结构，但是居里温度及相变潜热均略低于纯净BaTiO₃.研究了Tb_1-xDy_xFe_2-y-Fe∶BaTiO₃双层膜和Tb_1-xDy_xFe_2-y-Fe∶BaTiO₃-Tb_1-xDy_xFe_2-y三层膜的ME效应.在2.8×10⁴A/m的磁场下，两者的横向ME电压系数均达其峰值，分别为6.225和26.25mV·(A·m^-1)^-1·cm^-1.并且，用掺杂BaTiO₃制备的双层膜和三层膜的横向ME电压系数均为相同条件下用纯净BaTiO₃制备的双层膜和三层膜的横向ME电压系数的1.5倍.另外由于不含铅，锆等有害物质，符合环保要求，因此采用掺杂BaTiO₃制备的磁电效应器件具有深入研究和应用价值.     

Magnetoelectric coupling induced multistate magnetization

Complex oxides provide an ideal playground for exploring the interplay among the fundamental degrees of freedom: structural (lattice), electronic (orbital and charge), and magnetic (spin). With trends toward device miniaturization, there is growing interest in combining electronic and magnetic properties into multifunctional thin-film materials for potential applications in novel versatile devices. Here, we report growth of ferromagnetic nanostructures on ferroelectric ($1?x$)[Pb(Mg_1/3Nb_2/3)O₃]???x[PbTiO₃] (PMN-PT) single crystals. With careful control of material composition and application of electric field direction and amplitude, we realized stabilization of both monoclinic and orthorhombic phases in the PMN-PT single crystals with the intrinsic rhombohedral phase. Multistate magnetization modulation has been realized through phase transformation control in the ferroelectric component. This finding promises multistate information recording through magnetoelectric effect.     

Magnetoelectric effect in layered composites with arc shape

Magnetoelectric (ME) layered Ni/PZT/Ni composites with arc shape have been prepared by using electroless deposition. The ME effect is measured by applying both constant and alternating magnetic fields in longitudinal and transverse directions. The longitudinal ME voltage coefficient is much larger than the transverse one. With the increase of arc length or decrease of curvature, the resonance frequency of layered arc Ni/PZT/Ni composites gradually decreases, while the maximum of the ME voltage coefficient of the composites increases monotonously. The influence of the arc length and the curvature on ME coupling is discussed. The flat interface between the ferromagnetic and the piezoelectric phases in layered ME composites is believed to provide large ME voltage coefficient.     

Magnetoelectric characteristics around resonance frequency under magnetic field in Pb(Zr,Ti)O3/Terfenol-D laminate composite

Dependence of magnetoelectric modulus and phasic difference on the bias magnetic field was studied in a magnetoelectric Pb(Zr, Ti)O₃/Terfenol-D laminate composite. The shifts of both magnetoelectric resonant peak and phasic bounce under the bias magnetic field lead to a nonlinear relationship between them. The acoustic velocity of Terfenol-D has a nonlinear dependence on magnetic field, resulting in a similar relationship between the acoustic velocity of the composite and magnetic field. As a result, the magnetoelectric modulus and phase around the resonance frequency exhibit very sensitive dependences on the bias magnetic field.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Magnetoelectric effect in composites of magnet,metal-cap,and piezoceramic

We report on the magnetoelectric (ME) effect in three-phase magnet-metal-cap-piezoceramic composites of a thickness-polarized Pb(Zr,Ti)O₃ disk bonded between two truncated conical brass caps and two thickness-magnetized NdFeB magnets along the thickness direction. The effect originated from the product of the magnetic attractive–repellent effect in the magnets and the amplified piezoelectric effect in the cap-disk assembly. The composites exhibited a ME voltage coefficient α_V of ∼2.6 mV/Oe in the non-resonance frequency range of 0.1–10 kHz with good voltage-field linearity in the field range of 10^-3–10 Oe, besides an enhanced α_V of 167.4 mV/Oe at a resonance frequency of 14.4 kHz. Compared to conventional two-phase and three-phase magnetostrictive material-contained ME composites, these composites possessed two distinct benefits of higher property-tailorable flexibility and requiring no external dc bias magnetic field to enable an obvious α_V. PACS 77.84.-S; 75.80.+q; 77.84.Dy; 77.65.-j; 85.80.Jm     

Dynamic phenomena connected with magnetic and antiferroelectric interactions in trirutiles

Dynamic effects caused by the magnetoelectric and antiferroelectric interactions in tetragonal antiferromagnets are studied. The analysis is based on the example of trirutiles that are a series of antiferromagnets with different exchange structures and orientation states. We are mainly dealing with the excitation by an alternating electric field E(t) of spin waves typical of these magnets (antiferroelectric resonance) and the nuclear magnetoelectric resonance connected with these interactions. In the first case, special emphasis is placed on specific magnons (antimagnons), where only the antiferromagnetism vectors L take part in oscillations, whereas the total ferromagnetism vector M remains unchanged. The nuclear magnetoelectric resonance can be generated by oscillations of both L and M caused by field E(t). In this way, the field contributes to the hyperfine field, which acts on the nuclear spins. It is shown that the magnetic and antiferroelectric interactions in the dynamics can manifest themselves both at high (usually, exchange) frequencies ωw_E (antiferroelectric resonance) and at rather low nuclear frequencies of ω_n?ω_E. Particular cases of magnetic structures (phases) are considered where field E(t) can excite not only antimagnons, but also quasiantiferromagnons that have lower eigenfrequencies than those of quasimagnons (relativistic and semirelativistic).     

Forced wave propagation and energy distribution in anisotropic laminate composites

Elastodynamic response of anisotropic laminate composite structures subjected to a force loading is evaluated based on the integral representations in terms of Green's matrices. Explicit and asymptotic expressions for guided waves generated by a given source are then obtained from those integrals by means of series expansions and the residue technique. Unlike to conventional modal expansions, such representations keep information about the source, giving an opportunity for a quantitative near- and far-field analysis of generated waves. An effective computer implementation is achieved by the use of fast and stable algorithms for the Green matrix, pole, and residue calculations. The potential of the model is demonstrated by examples of anisotropy manifestation in the directivity of radiated waves. The effect of main energy outflow in the direction of either upper- or inner-ply orientation depending on the source size and frequency is discussed.     

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.     

Magnetoelectric interaction and magnetic field control of electric polarization in multiferroics

Various aspects of magnetic field control of magnetoelectric (ME) and electric properties of multiferroics are considered: linear ME effect appearance at magnetic field-induced incommensurate–commensurate phase transition, polarization switching and reversal by magnetic field and magnetic field-induced polarization flop transition. The correlation between magnetic, electric, and magnetoelastic properties is shown.     

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.     

Magnetoelectric effect and magnetic dynamics in the Gd2CuO4 antiferromagnet

The magnetoelectric effect and the magnetic dynamics in Gd₂CuO₄ have been studied using a phenomenological approach and group-theory methods. Vector order parameters are introduced based on four magnetic sublattices. Invariant products of the order parameters are determined, from which the thermodynamic potential density is constructed. Using the spin-wave representation, the calculations can be significantly simplified and the ground orientation magnetic state can be presumably determined. The magnetic dynamics is described by the Landau-Lifshitz equations, from which the antiferromagnetic resonance frequency and the dynamic susceptibilities, namely, magnetic, antiferromagnetic, magnetoelectric, and antiferroelectric susceptibilities are found. The frequency and the susceptibility are shown to be controlled by applied electric field.     

Phase switching phenomenon in magnetoelectric laminate polymer composites: Experiments and modeling

This article reports on the magnetoelectric (ME) effect observed in bi- and trilayered polymers consisting of polyvinylidene fluoride (PVDF) and polyurethane (PU) filled with magnetically hard magnetite Fe₃O₄ or Terfenol-D(TeD) magnetostrictive material. The samples had the following compositions: (PU+2 wt% Fe₃O₄/PVDF), (PU+2 wt% Fe₃O₄/PVDF/PU+2 wt% Fe₃O₄), (PU+50 wt% TeD/PVDF) and (PU+50 wt% TeD/PVDF/PU+50 wt% TeD). A model, based on a driven damped oscillation system, has been developed to evaluate and study the influence of the first and second-order ME coefficients on the dc magnetic field-induced phase switching phenomenon between dynamic ME current and the applied ac magnetic field. A good agreement between the simulated results and experimental data was obtained and it was found that phase switching characteristics are mainly influenced by the ME losses induced by magnetostriction losses.     

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象.     

Magnetoelectric coupling driven dielectric anomaly in non-polar system SeCuO3

The non-polar material SeCuO₃, which contains Cu²⁺ with S=1/2$S=1/2$ spin and Se⁴⁺, has a highly distorted perovskite structure due to the small radii of Se⁴⁺ cations. The dielectric constant displays a critical decrease at 25 K, at which temperature the ferromagnetic ordering of the Cu²⁺ spin appears, suggesting a strong coupling between the magnetic and dielectric properties. Studies on SeCuO₃ show that the magnetic and electrical subsystems reciprocally correlate via the hybridization of sp and pd. We conclude that the spin–pair correlation along the b-axis plays a significant role in the decrease of the dielectric constant around the magnetic transition temperature via the magnetoelectric coupling, and successfully explain the dielectric anomaly. The obtained dielectric constant and the magnetocapacitance for SeCuO₃ are quantitative agreement with experimental results.     

Magnetoelectric coupling effect of polarization regulation in BiFeO_3/LaTiO_3 heterostructures

An effective regulation of the magnetism and interface of ferromagnetic materials is not only of great scientific significance, but also has an urgent need in modern industry. In this work, by using the first-principles calculations, we demonstrate an effective approach to achieve non-volatile electrical control of ferromagnets, which proves this idea in multiferroic heterostructures of ferromagnetic La TiO_3 and ferroelectric Bi FeO_3. The results show that the magnetic properties and two-dimensional electron gas concentrations of La TiO_3 films can be controlled by changing the polarization directions of Bi FeO_3. The destroyed symmetry being introduced by ferroelectric polarization of the system leads to the transfer and reconstruction of the Ti-3 d electrons, which is the fundamental reason for the changing of magnetic properties.This multiferroic heterostructures will pave the way for non-volatile electrical control of ferromagnets and have potential applications.     

Magnetoelectric coupling in RMn2O5 multiferroic: a Monte Carlo simulation

Magnetoelectric coupling in RMn₂O₅ (with R?=?non magnetic) multiferroics have been studied using the Monte Carlo simulation. The variation of magnetization and the polarization of RMn₂O₅ multiferroic have been determined. The system undergoes a magnetic transition at T_N and a further reduction of the temperature leads to a ferroelectric transition at T_C?<_? T_N depending on the coupling strength. Magnetic and ferroelectric hysteresis loops are obtained for several temperatures values. Variation of polarization with the external magnetic field of RMn₂O₅ has been given. Variation of polarization and magnetization with the electric field of RMn₂O₅ has been obtained.     

Electrodynamics of Magnetoelectric Media and Magnetoelectric Fields

The relationship between magnetoelectricity and electromagnetism is a subject of a strong interest and numerous discussions in microwave and optical wave physics and material sciences. The definition of the energy and momentum of the electromagnetic (EM) field in a magnetoelectric (ME) medium is not a trivial problem. The question of whether electromagnetism and magnetoelectricity can coexist without an extension of Maxwell's theory arises when the effects of EM energy propagation are studied and the group velocity of the waves in an ME medium is considered. The energy balance equation reveals unusual topological structure of fields in ME materials. Together with certain constraints on the constitutive parameters of a medium, definite constraints on the local field structure should be imposed. Analyzing the EM phenomena inside an ME material, the question “what kind of the near fields arising from a sample of such a material can be measured?” should be answered. The visualization of the ME states requires an experimental technique that is based on an effective coupling to the violation of spatial as well as temporal inversion symmetry. To observe the ME energy in a subwavelength region, it is necessary to assume the existence of first-principle near fields—the ME fields. These are non-Maxwellian near fields with specific properties of violation of spatial and temporal inversion symmetry. A particular interest to the ME fields arises in studies of metamaterials with “artificial-atoms” ME elements.