多铁性复合材料磁电耦合效应研究进展

多铁性材料由于同时具有铁电有序和磁性有序并且在这两种有序态之间存在耦合效应,使其在电容器、传感器、存储器、自旋电子器件等领域具有广泛的应用前景而备受关注。然而,单相多铁性材料难以在室温下实现强的磁电耦合效应从而限制其实际应用。通过将具有强压电效应的铁电相与强磁致伸缩效应的铁磁相复合而成的多铁性材料理论上可获得室温下强的磁电耦合效应。但是,复合多铁性材料的磁电耦合效应与组成复合材料自身的性能、磁电相的体积比、测试条件(电磁场大小、频率)以及磁电相的连接方式等因素相关。其中,连接方式是调控磁电耦合效应的重要因素,也是目前研究的热点问题。目前连接方式也较多,如何通过连接方式的调控提高复合多铁性材料的磁电耦合效应极其重要。为此,综述了国内外通过连接方式来调控多铁性材料磁电耦合效应的研究进展,并提出了一些亟待解决的问题。     

多铁性氧化物基磁电材料的制备及性能

多铁性材料由于其不但具有单一的铁性(如铁电性、铁磁性和铁弹性),而且由于铁性的耦合协同作用,会产生一些新的效应,使其可广泛应用于换能器、传感器、敏感器、多态存储等高技术领域。而氧化物基单相/复相陶瓷及其薄膜材料(如BiFeO_3,铁氧体/锆钛酸铅等),由于其良好的铁磁、铁电性能,正成为磁电材料的研究热点。本文综合介绍了几种单相、复合磁电陶瓷、薄膜材料的制备,论述了材料的显微结构与磁电性能之间的关联,并指出了该类材料存在的问题和今后的发展方向。单相磁电材料至今还没能应用到实际中,主要是因为大部分单相材料的Neel或Curie温度较低,在很低的温度下才有磁电效应,磁也转换系数随着温度升高到室温而趋于零。具有低漏导的BiFeO_3薄膜(具有高的Curie温度)将具有铁电应用,但作为多铁性应用,还需解决弱的磁电耦合性。虽然复合磁电材料性能比单相材料性能好,但是仍然存在一些问题。磁电多铁性材料具有潜在的巨大的商业应用前景,已使其成为新的研究热点。     

0-X型磁电复合材料耦合效应研究进展

综述了国内外0-X型复合多铁性材料磁电耦合效应的研究进展。由磁性纳米微粒与铁电相复合而成的0-X型磁电复合多铁性材料具有更大的界面面积、更好的分散性以及因磁性相之间较差的连通性所带来的高阻特性等优点,理论上可获得室温下更强的磁电耦合效应。但是,0-X型磁电复合多铁性材料的磁电耦合效应不仅与铁电相和铁磁相本身有关,还依赖于两相的界面、尺寸、外延应变以及连接形式等因素,其中,磁电相之间的连接形式直接决定了复合材料中磁电相的分散性、界面面积及界面之间的作用力大小,进而影响磁电复合多铁性材料的磁电耦合性能。     

巨磁电阻在数据存储领域的应用

用巨磁电阻 (GMR)材料构成的磁电子学新器件,已成功地应用于计算机存储领域。介绍了用于计算机硬磁盘驱动器的巨磁电阻磁头和巨磁电阻随机存取存储器,描述了它们的工作原理、性能特点及研究现状和发展趋势。     

多铁性材料BiFeO3的磁学、电学性质及磁电耦合效应

磁电多铁性材料中电荷和自旋序参量共存,并相互耦合在一起,产生磁电耦合效应。由于磁电耦合效应在未来高密度、低能耗、高读写速率器件的重要应用前景,近10年来,多铁性材料的研究成为了材料科学以及凝聚态物理领域的热点之一。BiFeO3不仅是为数不多的铁电反铁磁的多铁性材料之一,更难能可贵的是它的铁电Curie温度和反铁磁Néel温度都远高于室温。正因为如此,BiFeO3早在60多年前就受到人们的关注;但是直到2003年高质量外延薄膜的出现,才真正掀起了人们对其卓越性能和新奇物理现象研究的热潮。正是在这个背景下回顾BiFeO3的发展历史,着重介绍近10年此领域的研究成果：从晶体结构、电学性质(巨大铁电极化、电致阻变效应等)、磁学性质(自旋螺旋结构)以及磁电耦合特性等角度,对由BiFeO3多铁性模型体系中衍生出来的新奇物理现象进行详细介绍。最后,就近几年相关领域的研究进行总结和研究展望。     

双钙钛矿型室温多铁性材料的研究进展

从多铁性材料和磁电耦合效应出发,介绍了双钙钛型室温单相磁电多铁性材料的研究进展,包括典型的Bi2(NiMn)O6、Bi2(CoMn)O6和Bi2(FeCr)O6块体材料和外延薄膜材料,在此基础上结合BiFeO3讨论了双钙钛矿结构材料存在的一些关键问题,最后对这些问题的解决提出了展望.     

多铁性材料的研究进展

多铁性材料是指材料的同一个相中包含两种及两种以上铁的基本性能.详细分析了两种类型的单相磁电材料的微观结构,并讨论了复合磁电材料的制备方法.     

多铁材料BiFeO3的元素掺杂研究进展

BiFeO3是一种在室温下同时存在铁电性,铁磁性的材料,在一定条件下可以产生磁电耦合效应。这种磁和电的相互作用提供了很多应用领域,包括数据存储器件,自旋电子学,磁电感应设备和多状态记忆领域,因此受到人们越来越多的关注。本文综述了对BiFeO3进行不同元素掺杂的一些研究进展,同时也指出了BiFeO3材料研究中存在的问题和发展方向。     

多铁性材料及其研究进展

综述了多铁性材料的发展,介绍了单相多铁性材料和复合多铁性材料的特点、改善单相多铁性材料和复合多铁性材料性能的途径,并对其发展前景进行了展望。     

金属卟啉-液晶超分子化学、光学特性综述

光信息处理和海量存储的需要合适的光信息存储器件,基于各种材料的光信息存储器主要包括无机晶体、有机聚合物和纯液晶等。基于无机晶体等的光信息存储器则需要数千伏的工作电压和数百毫瓦/平方毫米的光记录功率,衍射效率最高为20-30%。液晶是广泛使用的显示器材。与偶氮苯系列和C60纳米材料系列相比,掺杂金属卟啉的液晶光折变具有突出优点,可以实现在弱记录光、低电压下工作的低功耗、长时间记忆,是新型光信息存储器件,其竞争力远远超过传统的无机光折变晶体和目前的有机光折变材料。     

发展中的磁电材料

磁电材料在磁记录等方面具有巨大的潜在应用价值。在过去的几十年内,人们对单相材料和复合材料的磁电效应进行了广泛的研究。只有磁矩有序和电偶极子有序共存的材料才会在磁场作用下极化或在电场作用下磁化。单相材料有一个很大的缺点,即其磁电感应即使在低温下也相当微弱,这就限制了其在实际器件里的应用。复合材料的磁电感应是通过材料中独立的压磁相和压电相或磁致伸缩相和压电相实现的。磁电层合材料巨大的磁电感应电压系数源于压电晶体的巨压电电压系数和磁致伸缩部分的巨弹性屈服度。本文主要阐述磁电颗粒复合材料和层合材料的研究现状并总结了一些重要结果。     

Magnetoelectric Laminate Composites: An Overview

Since the turn of the millennium, giant magnetoelectric (ME) effects have been found in laminated composites of piezoelectric and magnetostrictive layers. Compared with ME single phase and two-phase particulate composites, laminated composites have much higher ME coefficients and are also readily fabricated. Here, we will overview the brief history of ME laminates, discussing some of the important advancements in material couples, laminate configurations, and operational modes that have allowed for dramatic enhancements in the ME voltage and charge coefficients.     

The Direct and the Converse Magnetoelectric Effect in Multiferroic Cobalt Ferrite–Barium Titanate Ceramic Composites

We report on a systematic study of the magnetoelectric effect in cobalt ferrite (CoFe₂O₄)—barium titanate (BaTiO₃) ceramic composites with (0‐3) connectivity. Both the converse magnetoelectric coefficient, α_C, and the direct voltage magnetoelectric coefficient, α^E, were measured in dependence on composition and electric and magnetic bias fields. The strongest ME effect was observed in the composition (1?x) CoFe₂O₄–xBaTiO₃ with x = 0.5 yielding values α_C = 25 psm^?1 and α^E = 3.2 mV/(cm·Oe). We show that the proper conversion between these two coefficients demands knowledge about the dielectric permittivity of the sample. For low BaTiO₃ content the dielectric coefficient of the composite yields a better correspondence, whereas for high BaTiO₃ content the sample's average dielectric coefficient yields a better match. The influence of mutual orientation of polarization and magnetization on the ME effect is addressed. We found that for measurements performed parallel to the polarization direction (longitudinal effect), the ME coefficient is approximately twice as large and of opposite sign in comparison to the measurements perpendicular to the polarization direction (transverse effect). This difference has been rationalized in terms of the different contributions of the material coefficient tensor components to the ME effect, the demagnetizing factor, and losses. The obtained results provide a better understanding of peculiarities of the ME effect in bulk ceramic composites.     

Dielectric behaviour and magnetoelectric effect in Ni0·25Co0·75Fe2O4-Ba0·8Pb0·2TiO3 ceramic composites

Abstract

Dielectric and magnetoelectric properties are reported in magnetoelectric (ME) composites containing lead doped barium titanate as the electrical component and a mixed Ni-Co ferrite as the magnetic component. Changes were observed in dielectric properties as well as in the ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 0·42 mV cm ^{- 1} Oe ^{- 1} (52·78 VA ^{- 1}) was observed in the composite containing 15 mol-% ferrite. Larger ME effects were observed in composites with higher contents of ferroelectric phase. This conclusion differs from earlier theoretical studies which predict a large ME interaction in composites with a 1:1 molar ratio of participating phases. Apart from the technological importance of the ME effect, some anomalies in magnetic phase transition induced by electric fields are also of scientific interest. The variation in dielectric properties with temperature resulted in two maxima, corresponding to the ferroelectric and ferrimagnetic Curie temperatures. This behaviour is unlike anything previously observed in other ME composites.     

Magnetoelectric response and tunneling magnetoresistance behavior of flexible P(VDF-H FP)/Cobalt ferrite nanofiber composite films

Fabrication of magnetoelectric (ME) polymer composite films by embedding ferromagnetic cobalt ferrite (CoFe₂O₄) nanofibers into electroactive poly(vinylidene fluoride–hexafluoropropylene) (P(VDF-HFP)) matrix is reported. Single-phase CoFe₂O₄ nanofibers made of cubic spinel nano crystallites are synthesized by using electro-spinning method, whereas the solution-casting technique is adapted to prepare flexible polymer composite films. The influence of CoFe₂O₄ nanofiber on structural, functional, magnetic, ferroelectric, and magnetoresistance properties of the composite films is investigated. The cross-coupling between ferroelectric and ferromagnetic orderings is ensured, by the variations of ferroelectric response at different magnetic fields. These magnetoelectric films are found to exhibit a negative tunneling magnetoresistance (TMR) effect with maximum TMR% of 28 for the film with 20 wt% of CoFe₂O₄ loading. The dielectric constant and electrical energy storage density of the films are increased with the addition of CoFe₂O₄ nanofiber. The ME films exhibiting TMR and high energy density can be the potential candidates for multifunctional device applications such as memory and spintronics devices, magnetic sensor, and bio-sensor.     

Magnetoelectric composite thick films of PZT–PMnN + NiZnFe2O4 by aerosol-deposition

Highly dense magnetoelectric composite films with 10 μm-thick of high piezoelectric voltage coefficient material, 0.9Pb(Zr₅₇Ti₄₃)O₃–0.1Pb(Mn_1/3Nb_2/3)O₃ (PZT–PMnN) and magnetostrictive material, Ni_0.8Zn_0.2Fe₂O₄ (NZF), were fabricated on a platinized Si substrate using aerosol deposition (AD). With increasing magnetic NZF content, dielectric and ferroelectric properties were gradually decreased while magnetizations were improved. The 20% NZF added composite thick film were found to exhibit the maximum ME coefficient. This optimal NZF content is the same as that of bulk ME composite materials. It is noticeable that AD can control the content ratio of ME composite films by controlling the powder composition. The fabricated ME composite films have high ME voltage coefficient coupling because of high density without severe inter-reactions of two phases.     

Effect of CoFe2O4 mole percentage on multiferroic and magnetoelectric properties of Na0.5Bi0.5TiO3/CoFe2O4 particulate composites

Na_0.5Bi_0.5TiO₃ (NBT), CoFe₂O₄ (CFO) as well as particulate composites containing different mole percentages of NBT and CFO were synthesized by the solid-state sintering route and characterized for their ferroelectric and ferrimagnetic hysteresis loops, magnetostriction and magnetoelectric (ME) output. The mole% of CFO was found to influence the ferroelectric and ferrimagnetic hysteresis loops as well as magnetostriction and piezomagnetic coefficients which in turn had a significant effect on the magnetoelectric voltage coefficient. The highest magnetoelectric voltage coefficient (α) of 0.5 mV/cm/Oe was recorded in (65) NBT–(35) CFO composite.     

Structure,electrical, optical and magnetoelectric properties of magnetron sputtered nanocrystalline NiFe/BaTiO3 thin films

BaTiO₃ (BTO) and NiFe films grown on SrTiO₃ (STO), Nb:SrTiO₃ (NSTO), and ITO-glass substrates were prepared by radio-frequency (RF) and direct-current (DC) magnetron sputtering, respectively. The microstructure, ferroelectricity, leakage current, magnetoelectric (ME) coupling, ultraviolet–visible light spectrum, optical band gap, ellipsometry spectrum and surface morphology of the composite film are characterized by XRD, ferroelectric analyzer, ME coupling test system, U-4100, Horiba Smart SE and AFM. In addition, the stress, strain and piezoelectric voltage of the magnetoelectric composite film under the action of DC and AC magnetic fields are simulated by COMSOL multiphysics software. The experimental results show that the prepared composite film is polycrystalline, the surface roughness of the film is better, and the particles are uniform. The magnetoelectric coupling voltage gradually increases with the increase of the value of the DC magnetic field and the frequency of the AC magnetic field, and it has a larger absorption (about 0.3) at 340 nm. In addition, the simulation results also show the relationship between the coupling voltage V_ME and the applied magnetic field H.     

Nanocrystalline Cellulose for Anisotropic Magnetoelectric Composites

The emergence of piezoelectric polymers in magnetoelectric (ME) composites enables flexible and low‐cost device fabrication though notably gives rise to the highest ME output voltages to date. Accordingly, the highest piezoresponsive polymers, poly(vinylidene fluoride) (PVDF) and its copolymers, are exclusively studied despite an inventory of unexplored piezoelectric polymers such as naturally occurring cellulose, that is only recently demonstrated in ME composites. Herein, the development of nanocrystalline cellulose (CNC)‐based ME composites is reported on. Two types of CNC, nanospheres and nanowhiskers, are synthesized and incorporated in laminate composite, which exhibit a giant α_ME (>1 V cm^?1 Oe^?1). By successfully reconstructing the orientated cellulose fibril structures found in natural plants using spinning‐induced alignment of CNC nanowhiskers, an anisotropic effect originating from the piezoelectric phase in ME composites is attained. The anisotropic effect produces output voltages an order of magnitude higher than those in current polymer‐based particulate ME vector sensing composites with 0–3 configurations.     

Modulation of magnetoelectric coupling through systematically engineered spin canting in nickel–zinc ferrite

A nickel–zinc ferrite system, which is one of the well-known versatile soft-ferromagnetic oxides, was investigated in terms of magnetoelectric (ME) coupling at room temperature. Herein, we demonstrated that spin canting is manipulated through a composition-induced structural transition from an inverse to a normal spinel structure, leading to modulation in the ME coupling. The ME coefficient was maximized at 60 at.% Zn substitution with a value of 0.1 mV/(Oe·cm), denoting ∼70% enhancement compared to that of the pure nickel ferrite. It was revealed that the interspin angle is enhanced along the octahedral site at up to ∼60 at.% Zn substitution, consistent with the composition level at the culmination of the ME coupling, evidenced by X-ray diffraction profiles and magnetic hysteresis loops combined with density functional theory calculations. Given that this approach is based on a tractable fabrication method, this study is expected to be widely used in modulation of the ME coupling in spinel-structured oxides.