Dielectric, ferroelectric, magnetic and magnetoelectric properties of PMN-PT based ME composites

A systematic study of magnetoelectric composite system (x) CoFe₂O₄+(1−x) Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ with x=0, 0.15, 0.30, 0.45 and 1 was carried out. The lattice strain was calculated using Williamson and Hall equation, which depends on the content of constituent phases in composites. The microstructure was studied using scanning electron microscopy. The ferroelectric transition temperature was independent of the content of individual phases, suggesting that the ferroelectric character is maintained in the composite. Observed P–E and M–H loops indicate that the multiferroic nature of magnetoelectric ceramics is dependent on the content of individual phases. The variation of magnetostriction with dc magnetic field was studied. The maximum magnetoelectric voltage coefficient of 7.2 mV/cm Oe is obtained for the synthesized composites. The magnetoelectric measurements are well explained with magnetostrictive behavior of the magnetic phase.     

K0.5Na0.5NbO3-LiSbO3-BiFeO3/CuFe2O4复合陶瓷的制备与磁电性能研究

采用传统的固相法制备了(1-x)(K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃)-xCuFe₂O₄ (x=0.1, 0.2, 0.3, 0.4) 磁电复合陶瓷, 并借助X射线衍射仪、扫描电镜和磁电耦合系数测试仪等对复合陶瓷的微结构和性能进行了分析. 结果表明, 复合陶瓷的K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃和CuFe₂O₄物相之间发生了一定的离子相互扩散作用, 且两相的颗粒大小匹配性较好. 随着CuFe₂O₄含量增加, 复合陶瓷的压电系数从130 pC/N减小到30 pC/N, 饱和磁致伸缩系数从4.5×10^-6增加到12.4×10^-6左右, 磁电耦合系数表现出先增加后减小, 在x=0.3时获得最大的磁电耦合系数9.4 mV·cm^-1·Oe^-1. 关键词： 0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃')" href="#">K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃ 2O₄')" href="#">CuFe₂O₄ 磁电耦合     

Synthesis, microstructures, and magnetoelectric couplings of electrospun multiferroic nanofibers

Multiferroic materials with two or more types of ferroic orders have attracted a great deal of attention in the last decade for their magnetoelectric coupling, and new ideas and concepts have been explored recently to develop multiferroic materials at nano-scale. Motivated by theoretical analysis, we synthesized single-phase BiFeO₃ (BFO) nanofibers, Pb(Zr_0.52Ti_0.48)O₃-CoFe₂O₄ (PZT-CFO) and Pb(Zr_0.52Ti_0.48)O₃-NiFe₂O₄ (PZT-NFO) composite nanofibers, and CoFe₂O₄-Pb(Zr_0.52Ti_0.48)O₃ (CFO-PZT) core-shell nanofibers using sol-gel based electrospinning. These nanofibers typically have diameters in the range of a few hundred nanometers and grain size in the range of 10s nanometers, and exhibits both ferroelectric and ferromagnetic properties. Piezoresponse force microscopy (PFM) based techniques have also been developed to examine the magnetoelectric coupling of the nanofibers, which is estimated to be two orders of magnitude higher than that of thin films, consistent with our theoretical analysis. These nanofibers are promising for a variety of multiferroic applications.     

Electrophoretic deposition of BaTiO3/CoFe2O4 multiferroic composite films

Electrophoretic deposition was utilized for preparation of BaTiO₃/CoFe₂O₄ multiferroic composite thick films on indium-tin oxide substrates. The suspensions for electrophoretic experiments were prepared by dispersing BaTiO₃ and CoFe₂O₄ nanoparticles with different molar ratios into solvents composed of ethanol and acetylacetone. Polyvinyl butyral was added to the suspensions in order to enhance the adhesion and strength of deposit and prevent cracking. The zeta potential values of BaTiO₃/CoFe₂O₄ suspensions were measured to be 26.4-36.9 mV. The experiment results showed that deposited films were obtained only when the applied electric field was larger than a certain critical value. XRD and SEM analysis depicted the presence of constituent phases in composite films. The percolation threshold of composite films was improved through dispersing ferromagnetic phase into ferroelectric phase. Therefore, the ferroelectric properties of composite thick films were maintained when the ferromagnetic properties were enhanced significantly with increasing CFO content.     

Role of electrodes materials in determining the interfacial and magnetoelectric properties in BaTiO<Subscript>3</Subscript>-based multiferroic tunnel junctions

Using the first-principles calculations based on density functional theory, the important role of electrode materials in determining the interfacial, ferroelectric stability and magnetoelectric properties in BaTiO₃-based multiferroic tunnel junctions (MFTJs) have been investigated comparatively. It is found that the SrO–TiO₂ interface of MFTJs with oxide electrode SrRuO₃ is the most favorable interfacial structure. The average ferroelectric polarizations of MFTJs with electrode Co, FeCo and SrRuO₃ are 25, 36 and 0 μC/cm², respectively. The using of alloy electrode FeCo is more contributed to ferroelectric stability and the enhancement of magnetoelectric coupling of BaTiO₃-based MFTJs. We expect our findings can provide an essential evaluation for the selection of electrode materials in spintronic storage devices.     

2-2型磁电复合薄膜CoFe2O4/Pb(Zr0.53Ti0.47)O3静磁耦合

运用溶胶-凝胶法在Pt/Ti/SiO₂/Si基片上旋涂制备了2-2型CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃磁电复合薄膜．制备的磁电薄膜结构为基片/PZT/CFO/PZT*/CFO/PZT,通过改变中间层PZT*溶胶的浓度,改变磁性层间距以及静磁耦合的大小．SEM结果表明,复合薄膜结构致密,呈现出界面清晰平整的多层结构．制备的复合薄膜具有较好的铁电与铁磁性能．实验还研究了静磁耦合对薄膜磁电性能的影响,结果表明,随着复合薄膜磁性层间距的减小,静磁耦合效应的增加,磁电电压系数有逐渐增大的趋势.     

Bismuth ferrite composite thin films

0.60Bi_0.90La_0.10FeO₃–0.40Pb(Zr_0.52Ti_0.48)O₃ composite thin films were deposited on Pt/TiO₂/SiO₂/Si(100) substrates by radio-frequency sputtering and their ferroelectric and fatigue properties were mainly investigated. The composite thin films have a low dielectric loss, a high dielectric constant, and enhanced ferroelectric properties of 2P _r～122.6 μC/cm² and 2E _c～479.3 kV/cm, together with a fatigue-free behavior at 200 kHz. Their fatigue behavior is strongly dependent on measurement frequencies, and the concentration of oxygen vacancies plays an important role in their fatigue behavior.     

Multiferroic behavior and magnetoelectric effect in CoFe2O4/Pb(Zr0.53Ti0.47)O3 thick films

A CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃ (CFO/PZT) multiferroic composite thick film assisted by polyvinylpyrrolidone (PVP) was prepared by a hybrid sol–gel processing and spin coating technique. Scanning electronic microscopy indicated a porous microstructure with a thickness of 6.2 μm. Pure PZT perovskite phase observed from x-ray diffraction suggested that the low ratio of CFO particles was deeply buried in the PZT matrix. Ferroelectric and ferromagnetic properties were observed simultaneously at room temperature as well as a lower leakage current compared with a CFO/PZT thin film. The dynamic and static magnetoelectric effects were strongly dependent on the applied DC/AC magnetic field but their values were very low. The results demonstrated the prediction that ferroelectric and ferromagnetic properties can induce a strong magnetoelectric coupling only if a dense microstructure was achieved.     

Studies on lead-free multiferroic magnetoelectric composites

Lead-free multiferroic magnetoelectric composites consisting of ferrimagnetic Ni_0.93Co_0.02Mn_0.05Fe_1.95O₄ (NMF) and ferroelectric Na_0.5Bi_0.5TiO₃ (NBT) phases were synthesized by the solid-state sintering method. The presence of constituent phases in composites was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A systematic study of dc conductivity as a function of temperature (RT −450 °C) revealed that the conduction is due to small polarons. The effect of constituent phase variation on the dielectric constant and piezoelectric strength (d₃₃) was examined. The composites exhibited typical magnetic hysteresis (M–H) loops at room temperature. Furthermore, magnetoelectric (ME) output was evaluated as a function of applied magnetic field, which is a product property of the constituent phases. The compound 50% NMF–50%NBT is a new lead-free magnetoelectric composite with 155 μV/cm ME output, which may have potential applications.     

Nucleation of electroactive β-phase poly(vinilidene fluoride) with CoFe2O4 and NiFe2O4 nanofillers: a new method for the preparation of multiferroic nanocomposites

Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials. In this paper we report on the nucleation of the electroactive β-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe₂O₄ and NiFe₂O₄ nanoparticles in order to prepare poly(vinylidene fluoride)/ferrite nanocomposite for multiferroic and magnetoelectric applications,. The dispersed ferrite nanofiller particles strongly enhance the nucleation of the β-phase of the polymer matrix. In this way, magnetoelectric polymer nanocomposites can be processed avoiding the usual α- to β-phase transformation by stretching of the polymer matrix.     

Terfenol-D/Pb(Zr,Ti)O3 Disk-Ring Multiferroic Heterostructures Coupled Through Normal Stresses

Disk-ring multiferroic heterostructures composed of Terfenol-D and Pb(Zr,Ti)O₃ (PZT) were prepared and characterized, for which the ferromagnetic and ferroelectric phases were coupled through normal stresses instead of the shear stresses that acted in most of the previous multiferroic heterostructures. High low-frequency magnetoelectric coefficients of 0.10–0.75 V cm⁻¹ Oe⁻¹ were attained for the disk-ring heterostructures, which indicated the strong magnetoelectric coupling. Moreover, a symmetrical resonant peak was observed for dE ₃/dH ₃ in the frequency range of 1–200 kHz, while another weak peak with asymmetrical shape also existed at a lower frequency for dE ₃/dH ₁, which was due to the combination of two vibration modes.     

Determination of the magnetoelectric coupling coefficient from temperature dependences of the dielectric permittivity for multiferroic ceramics Bi5Ti3FeO15

In the multiferroic materials, the dielectric and magnetic properties are closely correlated through the coupling interaction between the ferroelectric and magnetic order. We attempted to determine the magnetoelectric coupling coefficient from the temperature dependences of the dielectric permittivity for multiferroic Bi₅Ti₃FeO₁₅. Multiferroic ceramics Bi₅Ti₃FeO₁₅ belong to materials of the Aurivillius-type structure. Multiferroic ceramics Bi₅Ti₃FeO₁₅ was synthesized via sintering the Bi₂O₃ and Fe₂O₃ mixture and TiO₂ oxides. The precursor material was ground in a high-energy attritorial mill for 5 hours. This material was obtained by a solid-state reaction process at T = 1313 K. We investigated the temperature dependences of the dielectric permittivity for the different frequencies. From the dielectric measurements, we determined the temperature of phase transition of the ferroelectric-to-paraelectric type at about 1013 K. Based on dielectric measurements and theoretical considerations, the values of the magnetoelectric coupling coefficient were specified.     

EFFECT OF ZnFe22O4 DOPING ON THE OPTICAL PROPERTIES OF TiO2 THIN FILMS

Amorphous TiO₂ thin films and ZnFe₂O₄ doped TiO₂ composite films were deposited by radio frequency magnetron sputtering. The effect of ZnFe₂O₄ doping on the optical properties of TiO₂ thin films was reported. Our results show that the absorption edge of TiO₂ thin films and composite films exhibits a blue shift with decreasing annealing temperature. The absorption edge of composite films has moved to visible spectrum range, and a very large red shift occurs in comparison with TiO₂ thin film. An enhanced photoluminescence in ZnFe₂O₄ doped anatase TiO₂ thin film at room temperature.     

SrBi2Ta2O9/Bi4Ti3O12复合铁电薄膜的制备与特性研究

采用溶胶凝胶工艺在p-Si衬底上制备了SrBi₂Ta₂O₉/Bi₄Ti₃O₁₂复合铁电薄膜. 研究了SrBi₂Ta₂O₉/Bi₄Ti₃O₁₂复合薄膜的微观结构与生长行为、铁电性能和疲劳特性. 研究表明: Si衬底Bi₄Ti< 关键词： 2Ta₂O₉')" href="#">SrBi₂Ta₂O₉ 4Ti₃O₁₂')" href="#">Bi₄Ti₃O₁₂ 复合铁电薄膜 溶胶凝胶工艺     

Elastic,magnetic, and magnetoelectric properties of the CaBaCo<Subscript>4</Subscript>O<Subscript>7</Subscript> multiferroic

The structural, elastic, magnetic, and magnetoelectric properties of the CaBaCo₄O₇ multiferroic are experimentally studied and compared with the properties of the related YBaCo₄O₇ cobaltite, where Y³⁺ ions substitute for Ca²⁺ ions. Unlike the frustrated YBaCo₄O₇ magnet, the softening of Young’s modulus and the hysteresis in the ΔE(T)/E ₀ curve of ferrimagnetic CaBaCo₄O₇ in the paramagnetic region are weak, and the anomaly during the magnetic transition increases by almost an order of magnitude. This difference can point to different characters of the development of a long-range magnetic order in these two cobaltites. The distortion of the crystal structure that removes the frustrations of exchange interactions is found to correlate with the magnetic behavior of the cobaltites under study. The magnetization curves of the Ca cobaltite have two steps below 15 K, which can point to the presence of a metastable state in a high magnetic field. The study of the longitudinal and transverse magnetoelectric effects in a pulsed magnetic field demonstrates that their magnitudes are maximal near T _C and change their character from linear to quadratic during passage through this temperature.     

Ferroelectric and dielectric properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> thin films grown on Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> film layer

Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi₄Ti₄O₁₅ grown on Bi₄Ti₃O₁₂, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared on a Pt(111)/Ti/SiO₂/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P _r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm² at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 10¹⁰ switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi₄Ti₄O₁₅ on Bi₄Ti₃O₁₂ ferroelectric thin films were better than those of the SrBi₄Ti₄O₁₅ grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth kinetics of SrBi₄Ti₄O₁₅ on the c-axis-oriented Bi₄Ti₃O₁₂ layer or on the Pt-coated Si substrate.     

Influence of cycling electric polarization on multiferroic behaviors in heterostructural films composed of ferroelectric and ferromagnetic oxides

The CoFe₂O₄/Pb(Zr_0.52Ti_0.48)O₃ bilayer films were prepared by a sol–gel process, and the influence of cycling electric polarization on the multiferroic behaviors of the bilayer films was studied. The ferroelectric polarization hysteresis loops under various choices of magnetic bias were measured by an integrating current method. The results showed that after undergoing cycling electric polarization the ferroelectric polarization of the bilayer films enhanced and the suppression of ferroelectric polarization by external magnetic bias remarkably weakened. Based on the measurements of activation energy and leakage current, we confirmed that the oxygen vacancy migration in the bilayer films occurred during cycling electric polarization. Furthermore, we analyzed the mechanism of the influence of cycling electric polarization on the multiferroic behaviors of the bilayer films and attributed it to the oxygen vacancy migration, which could cause a part of ferroelectric domains to be unpinned from the oxygen vacancies and become more active under electric field and magnetic bias.     

Piezoresponse force microscopy and magnetic force microscopy characterization of γ-Fe2O3-BiFeO3 nanocomposite/Bi3.25La0.75Ti3O12 multiferroic bilayers

The multiferroic behavior of epitaxial γ-Fe₂O₃-BiFeO₃ (composite)/Bi_3.25La_0.75Ti₃O₁₂ bi-layered heterostructures grown on SrRuO₃/SrTiO₃ (1 1 1) substrates has been studied using piezoresponse force microscopy, magnetic force microscopy and magnetometry. The ferroelectric domain structure is ascribed to the BiFeO₃ phase while the magnetism originates in the γ-Fe₂O₃ phase of the composite layer. Our studies demonstrate the presence and switching of magnetic and ferroelectric domains within the same area of the sample. This confirms the presence of multiferroic behavior at the nanoscale in our γ-Fe₂O₃-BiFeO₃ nanocomposite thin films.     

Microstructure-property relationship in magnetoelectric bulk composites

We present systematic studies that comprise phase connectivity and dielectric, multiferroic (MF) and magnetoelectric (ME) properties of (x) Ni_0.8Co_0.2Fe₂O₄+(1−x) Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ [where x=0.15, 0.30 and 0.45] ME composites prepared by conventional solid-state reaction method. Scanning electron microscopic images of the composites predict different types of connectivity schemes viz 3-0, 3-1 and 3-3. The phase transition temperature of PMN-PT is independent of Ni_0.8Co_0.2Fe₂O₄ content. Room temperature P-E and M-H loops indicate the simultaneous existence of ferroelectric/magnetic ordering. In order to study the possibility of monitoring electrical ordering by means of a magnetic field, ME measurements were carried out. The composition-dependent phase connectivity was well co-related to formation of percolation path and inturn magnetoelectric output.     

溶胶-凝胶法制备Sr2Bi4Ti5O18薄膜及其铁电性能研究

采用溶胶-凝胶法,在氧气氛中和层层晶化的工艺条件下,成功地制备了沉积在Pt/Ti/SiO₂/Si(100)衬底上的铁电性能优良的Sr₂Bi₄Ti₅O₁₈ (SBTi)薄膜,并研究了SBTi薄膜的微结构、表面形貌、铁电性能和疲劳特性.研究表明：薄膜具有单一的层状钙钛矿结构，且为随机取向；薄膜表面光滑，无裂纹，厚度约为725nm；铁电性能测试显示较饱和、方形的电滞回线，当外电场强度为275kV/cm时 关键词： 溶胶-凝胶法 铁电薄膜 2Bi₄Ti₅O₁₈')" href="#">Sr₂Bi₄Ti₅O₁₈