压电-磁致伸缩双层磁电复合材料的机电谐振

基于压电相和磁致伸缩相的本构方程以及弹性体的运动方程,简要推导了一维机电谐振模式下压电-磁致伸缩双层磁电复合材料横向磁电电压系数的表达式。采用相应的材料参数计算分析了Tb_1-x Dy_x Fe_2-y (TDF)-Pb(Zr,Ti)O₃(PZT)双层磁电复合材料的横向磁电电压系数与交流磁场频率的关系,以及复合材料的长度和压电相体积分数对机电谐振频率的影响。计算与分析结果表明,双层磁电复合材料在机电谐振频率处具有明显的磁电 响应特性。当有效机械品质因数为50,在谐振频率55.2 kHz处横向磁电电压系数达到峰值11.2 V·cm^-1·Oe^-1,是低频下峰值(281.9 mV·cm^-1·Oe^-1)的40倍。机电谐振频率随复合材料长度的减小和压电相体积分数的增加而上升。实验结果说明TDF-PZT双层磁电复合材料在机电谐振频率处具有显著增强的磁电效应,实际有效机械品质因数约为48。     

热处理温度对FeCoSiB薄膜及FeCoSiB/Cu/FeCoSiB三明治膜应力阻抗效应的影响

采用DC磁控溅射法在玻璃基片上制备了FeCoSiB薄膜和FeCoSiB/Cu/FeCoSiB 三明治膜,并进行磁场退火热处理以消除残余应力和形成磁织构,提高薄膜的应力阻抗效应。薄膜的磁性能采用振动样品磁强计(VSM)进行测试,采用HP4275A 型阻抗分析仪在200kHz~10MHz频率范围内测试薄膜的应力阻抗效应。结果表明,磁场退火热处理可形成感生磁各向异性,改善薄膜的软磁性能、提高薄膜的应力阻抗效应。在温度低于300℃时,随着退火温度的增加,薄膜的应力阻抗效应增大;当退火温度超过300℃时,薄膜的应力阻抗效应随退火温度增加而降低。与Fe CoSiB单层膜相比, FeCoSiB/Cu/FeCoSiB 三明治膜应力阻抗效应较大。10MHz测试频率下,在基片末端位移为450μm时,经300℃热处理的三明治膜达到了8.3%,而单层膜仅有1.86%。当测试频率较高为10和4MHz时,薄膜的应力阻抗效应变化不大,当测试频率下降到低于1MHz时,薄膜的应力阻抗效应显著降低。     

Ba_(0.8)Sr_(0.2)TiO_3/CoFe_2O_4异质结层状多铁复合薄膜的制备与性能

利用射频磁控溅射法在Pt(200)/TiO_2/SiO_2/Si(100)衬底上沉积Ba_(0.8)Sr_(0.2)TiO_3/CoFe_2O_4异质结层状多铁磁电耦合复合薄膜。Ba_(0.8)Sr_(0.2)TiO_3/CoFe_2O_4异质结复合薄膜为多晶,由钙钛矿Ba_(0.8)Sr_(0.2)TiO_3相和尖晶石CoFe_2O_4相组成。复合薄膜表现为良好的铁电性和铁磁性共存。在测量磁场平行于样品表面情况下测得的复合薄膜的饱和磁化强度(M_s)、剩余磁化强度(M_r)值要大于在测量磁场垂直于样品表面时测得的M_s、M_r值。另外,复合薄膜具有直接的磁电耦合效应,磁电电压系数αE先随着偏置磁场H_(dc)的增大而增大,当偏置磁场H_(dc)增加到445.8kA/m后,αE反而随偏置磁场的增加而减少。当偏置磁场H_(dc)=445.8kA/m时,复合薄膜具有最大的磁电电压系数αE=18.8mV/A。     

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。      

NiFeCr/NiFe/MgO/Ta薄膜制备及热处理研究

采用磁控溅射制备了NiFeCr(4.5nm)/NiFe(10nm)/MgO(4.0nm)/Ta(5.0nm)薄膜,并对薄膜进行真空磁场退火。退火后薄膜磁电阻变化率显著提高,400℃退火后达到3.02%,之后随着退火温度的升高,磁电阻变化率下降。XRD结果表明,薄膜不仅具有很强的NiFe(111)织构,同时还出现了MgO的(111)衍射峰。随退火温度的升高,MgO(111)衍射峰的强度有所降低。     

流延成型法制备2-2型多层(CoFe_2O_4-Pb(Zr_(0.52)Ti_(0.48))O_3)_n磁电复合薄膜

运用流延成型法制备了具有良好铁电铁磁性能的2-2型多层(CoFe_2O_4-Pb(Zr_(0.52)Ti_(0.48))O_3)_n[(CFOPZT)n]磁电复合薄膜。通过X射线衍射仪、扫描电镜、振动样品磁强计和铁电测试仪测试研究了(CFO-PZT)n复合薄膜的组织结构、铁磁和铁电性能。结果表明,钙钛矿结构的PZT和尖晶石结构的CFO相对均匀地分布在多层复合薄膜各层中,界面平整均匀。随热处理温度的升高,薄膜致密度提高,晶粒长大,但相结构未变,无新相形成。900℃热处理的(CFO-PZT)n复合薄膜结晶更完善,磁电性能好,剩余极化强度为32.63μC/cm~2,饱和磁化强度高达80.56kA/m,在2.29×10~4 A/m偏置磁场处有最大磁电耦合系数17.69kV/(cm·T)。     

磁电复合结构磁场传感器灵敏度的电压调控研究

目的:实现外加激励电压调节磁电复合结构磁场传感器灵敏度的方法。方法:通过实验测量三层磁电复合结构磁电传感器,在压电调控层上施加不同电压时的磁电响应特性和灵敏度的变化。结果:无论是在静态还是在谐振状态,通过改变压电调控层的调控电压,均可以有效调节磁电传感器的灵敏度;在不同的谐振状态和不同的DC磁场段,外加调控电压调节传感器灵敏度变化的趋势不一样。特别是在共振频率为43 kHz的一阶弯曲共振模式,在调控电压变化400 V的范围内,传感器的灵敏度变化高达47.59%。结论:实验测量结果证实了压电调控层上外加调控电压调节磁电传感器灵敏度的可行性。     

FeCoSiB薄膜应力阻抗性能的的影响因素及提高方法

利用磁控溅射方法在玻璃基片上制备了FeCoSiB薄膜，溅射过程中施加一横向静磁场，并在真空中退火。实验结果表明，FeCoSiB的应力阻抗效应与制备工艺（工作气压、溅射磁场）和退火条件（退火温度、退火时间）有着非常密切的联系。当偏置磁场从60 Oe增加到120 Oe时，薄膜的应力阻抗从0．5％提高到了1．65％。在80 Oe磁场下，薄膜经300℃、40min退火处理后，应力阻抗效应达1．86％。     

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。     

多铁性BaTiO3/La2/3Sr1/3MnO3复合薄膜的制备及其强磁电效应的研究

使用脉冲激光沉积技术,在(001)取向的LaAlO3(LAO)单晶基片上外延生长了BaTiO3/La2/3Sr1/3MnO3(BTO/LSMO)双层复合薄膜.电学和磁学性能的研究显示复合薄膜具有较低的相对介电常数(εr=263),优良的铁电和铁磁性能以及高于室温的铁磁居里温度(Tc=317 K).复合薄膜的磁电电压系数(αE)为176 mV/A,高于同类结构磁电系统一个数量级,相应的界面耦合系数k值为0.68,表明铁磁层和铁电层界面之间存在较大程度的耦合.     

Magnetoelectric properties of Ni/PZT/Ni layered composite for low field applications

A composite material when placed under the external magnetic/electric fields exhibits voltage/induced magnetization is known as magnetoelectric (ME) composite. Such composite materials should have ferroelectric and ferro/ferri magnetic phases as constituents. The magnetoelectric output is exhibited as a product property. Magnetoelectric composites are being used for variety of applications including resonators, filters, phase shifters, optical isolators, actuators and magnetic field sensors. Metal/ferroelectric/metal magnetoelectric composite using Ni and PZT as constituent phases has been fabricated in 2-2 composite pattern to study its product property. The paper presents magnetoelectric studies of Ni/PZT/Ni composite using low dc magnetic field magnetoelectric set-up. Using this ME set-up ME output of Ni/PZT/Ni composite is studied as a function of dc magnetic field. The results were analyzed to identify the useful magnetic field (dc and ac) range in which Ni/PZT/Ni sensor can be utilized for applications.     

Magnetoelectric Performances in Composite of Piezoelectric Ceramic and Ferromagnetic Constant-Elasticity Alloy

A high-quality factor magnetoelectric (ME) laminated composite employing a type of ferromagnetic constant-elasticity alloy (FCEA) and piezoelectric Pb(Zr,Ti)O₃ material is developed. The laminate is designed to operate as a half-wavelength (lambda/2), longitudinal resonator. The FCEA features high effective quality factor and low magnetomechanical coupling coefficient. This induces a particular ME characteristic. The theoretical analysis shows that the ME voltage coefficient (MEVC) at low frequency is directly proportional to the product of the electromechanical coupling factor in piezoelectric layer, magnetomechanical coupling factor, and the square root of magnetic permeability in FCEA layers. The MEVC at resonance and the ME sensitivity (under resonant drive) to dc bias magnetic field (H _dc) are dramatically increased by the effective quality factor (Qm) of the resonator. The measured vibrational characteristics reveal that the strain coefficient at resonance achieves 314.74 nm/A and Qm is ~ 1600. The MEVC at resonance (alphar) achieves 30.55 V/Oe (381.875 V/cm Oe), which is 1608 times higher than that at low frequency. In addition, alphar strongly depends on H _dc due to the high Qm, e.g., partalphar/partH _dc achieves 0.84 V/Oe². The ME resonator is potential for highly sensitive dc or quasi-static magnetic field sensing.     

膜/块体结构氧化物复合磁电材料研究进展

由铁氧体(如: CoFe₂O₄, NiFe₂O₄)和铁电相(如: BaTiO₃, Pb(Zr_xTi_1-x)O₃)组成的复合材料是经典的复合磁电材料, 也是最早在室温下观察到大磁电耦合效应的复合材料。这类复合材料的制备通常是在高于1200℃的高温条件下将铁氧体相和铁电相两相共烧而成。然而, 在高温过程中不可避免的存在原子互扩散及两相界面反应, 甚至出现微裂纹。本文综合介绍了几种通过直接在一种铁性氧化物块体上生长另一种铁性陶瓷膜的方法, 从而实现铁电、铁磁两相之间的低温复合(一般不高于800℃), 避免了高温共烧过程中的固有问题, 并展示了此类膜/块体复合体系的磁电耦合性能常用的表征方法。     

低温烧结CoFe2O4-(PZN-PZT)多铁复合材料磁电性能研究

采用传统陶瓷工艺和低温烧结制备了CoFe₂O₄-(PZN-PZT)多铁复合陶瓷, 研究了混合方式、PZT包覆和成分变化对其结构、磁性能、磁电耦合性能的影响。XRD图谱和TEM照片显示, 采用溶胶-凝胶和包覆搅拌混合的方法获得了CoFe₂O₄/PZT核壳结构粉末, 在CoFe₂O₄表面形成了10~20 nm的钙钛矿PZT壳层。EDS结果显示, 低温烧结和阻挡层可以有效抑制两相间的元素扩散。SEM照片和磁电性能结果显示, 相对未包覆研磨混合工艺, 包覆搅拌混合可以提高磁性颗粒复合含量, 获得较好烧结匹配性, 有效提高材料的磁电耦合性能。研究结果表明, 包覆搅拌混合制备体积比为4:6的CoFe₂O₄-(PZN-PZT)样品, 经1000℃烧结, 在10 kHz下获得最大磁电耦合系数(18.3 mV/(cm·Oe))。     

Magnetoelectric coupling of Terfenol-D/P(VDF-TrFe)/Terfenol-D laminates mediated by crystallite size of electroactive polymer

The attention here is focused on the magnetoelectric (ME) coupling in Terfenol-D/P(VDF-TrFE)/Terfenol-D laminated composites. The electroactive P(VDF-TrFE) 75/25mol% copolymer films were prepared using three different annealing conditions: 135°C for 2h , 6h and 140°C for 2h. The results show that the laminate with the copolymer film annealed at 135°C for 2h exhibits the highest ME coupling, while the one with the copolymer film annealed at 140°C for 2h shows the lowest. Microstructure examination demonstrates that the crystallites grow significantly in size with either the annealing time or the temperature although the crystallinity increases slightly. It is suggested that the copolymer film with smaller crystallite size, or higher volume fraction of the amorphous/crystallite interfacial layers, is beneficial to the piezoelectric effect and consequently the ME coupling of the laminated composites.     

Magnetoelectric properties of Ba0.8Sr0.2TiO3–CoFe2O4 multilayered composite film via sol–gel method

Ba_0.8Sr_0.2TiO₃–CoFe₂O₄ (BST–CFO) multilayered composite films were prepared on Pt/Ti/SiO₂/Si substrates via a sol–gel method and spin-coating technique. Microstructures, electric property, magnetic property and magnetoelectric (ME) property of the composites were studied. Results show that the composite films calcined at 750 °C have BST and CFO phases and no obvious impurity phases were detected. Further, the composite films exhibit layered structures and a transition layer which is composed of interfacial delamination exists at the interface between BST and CFO layers. Ferroelectric and ferromagnetic properties were simultaneously observed in the films, evidencing the coexistence of the ferroelectric and ferromagnetic properties. Furthermore, the saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic BST layers. Also, ferroelectric hysteresis loops reveal that the saturated polarization and remanent polarization of the composite film are lower than those of the pure BST films. In addition, the composite film exhibits a strong ME effect, which makes the composite film attractive for technological applications as devices.     

Magnetoelectric effect in metal-PZT laminates

Magnetoelectric (ME) composites are two-phase composites consisting of piezoelectric and piezo-magnetic materials as the participating constituents. These magnetoelectric composites when placed under external magnetic field, show electrical polarization (magnetoelectric output). The ME coupling is mediated by mechanical stress. In the present study, we have synthesized Ni/PZT/Ni and Fe/PZT/Fe layered composites for studying their ME output by dynamic magnetoelectric set up in which both d.c. and a.c. magnetic fields can be varied. The ME output obtained in these composites are higher than those obtained in 40% Ni_0.97Co_0.03Mn_0.01 Fe_1.9O₄ + 6O%BaTi_1.02O_3.04. The results with varying d.c. and a.c. magnetic fields are presented.     

Magnetic field-induced strain and magnetoelectric effects in sandwich composite of ferromagnetic shape memory Ni-Mn-Ga crystal and piezoelectric PVDF polymer

A sandwich composite consisting of one layer of ferromagnetic shape memory Ni-Mn-Ga crystal plate bonded between two layers of piezoelectric PVDF polymer film was fabricated, and its magnetic field-induced strain (MFIS) and magnetoelectric (ME) effects were investigated, together with a monolithic Ni-Mn-Ga crystal, as functions of magnetic fields and mechanical load. The load-free dc- and ac-MFISs were 0.35 and 0.05% in the composite, and 5.6 and 0.3% in the monolithic crystal, respectively. The relatively smaller load-free MFISs in the composite than the monolithic crystal resulted from the clamping of martensitic twin-boundary motion in the Ni-Mn-Ga plate by the PVDF films. The largest ME coefficient (α(E)) was 0.58 V/cm·Oe at a magnetic bias field (H(Bias)) of 8.35 kOe under load-free condition. The mechanism of the ME effect originated from the mechanically mediated MFIS effect in the Ni-Mn-Ga plate and piezoelectric effect in the PVDF films. The measured α(E)-H(Bias) responses under different loads showed good agreement with the model prediction.     

Magnetoelectric effect of the multilayered CoFe2O4/BaTiO3 composites fabricated by tape casting

This paper presents the structural, ferroelectric, ferromagnetic, resonance and magnetoelectric (ME) properties of multilayered ME composites fabricated using tape casting method. The compositions corresponding to CoFe₂O₄ (CFO) with particle size of ~150?nm and BaTiO₃ (BTO) with particle size of ~100?nm were chosen as ferromagnetic and ferroelectric phases, respectively. Delamination was found at the interface between CFO and BTO layers, which was related to the residual stress due to the difference in thermal expansion coefficient between the two layers. The largest direct magnetoelectric and converse magnetoelectric coefficients of the multilayered ME composite were, respectively, 36?μV/cm?Oe at a bias magnetic field of 2,800?Oe and 1.16?×?10^?3?G/V at a frequency of 30?kHz. In addition, the corresponding interfacial coupling coefficient was calculated to be 3.2?×?10^?5. For the multilayered ME composite, a resonance frequency of 4.96?MHz and a bandwidth of 40?kHz were obtained using capacitance-frequency spectrum method.     

水热合成CoFe_2O_4/Bi_(0.5)Na_(0.5)TiO_3颗粒磁电复合材料中的零偏置现象

通过水热法分别制备CoFe_2O_4和Bi0.5Na0.5TiO3纳米粉。将两种粉末均匀混合,经成型和共烧工艺制备了xCFO-(1-x)BNT颗粒复合磁电材料(质量分数x为0.3,0.4,0.5)。X射线衍射(XRD)和SEM扫描电子显微镜(SEM)分析表明,复合陶瓷保持了较纯净的钙钛矿(BNT)和尖晶石结构(CFO)。振动样品磁强计(VSM)测试表明,这种材料在室温下具有良好的铁磁性。当磁场频率为1KHz时,950℃烧结的复合磁电材料(x=0.3)具有最大的磁电转换系数,约为47.4mV/Oe·cm;且发现当磁场为零时,该复合材料磁电转换系数不为零,在谐振点处仍具有1.2V/Oecm的磁电转换系数。这是一种可以应用于零场和中频的磁电复合材料。