CoFe2O4 Content Research Articles

BaTiO<sub>3</sub>薄膜におけるCoFe<sub>2</sub>O<sub>4</sub>ナノピラーの形成に伴い生じる界面応力

CoFe2O4(CFO)-doped BaTiO3(BTO) film is one of composite multiferroic materials. In the materials, magnetoelectric effect occurs from the stress of the interface between ferroelectric and ferromagnetic. Therefore, Interfacial stress between BTO and CFO is important for magnetoelectric effect. However, it has not been clearly yet. It is considered that it can reveal the effect on BTO of CFO to comparing different CFO content samples. Then, we fabricated CFO-doped BTO films with various content and measured lattice constant and temperature dependence of dielectric constant for films. As a result, out-of-plane lattice constant of BTO was reduced with the increase of the CFO content. In addition, phase transition temperature of BTO was increased with the increase of the CFO content. Therefore, it is considered that CFO adds some in-plane tensile stress on BTO.

Improved magnetodielectric coefficient on polymer based composites through enhanced indirect magnetoelectric coupling

Flexible particulate composites with general formula [xCoFe2O4]/[(1 − x) (Polyvinylidene fluoride)] were prepared for x = 0, 3, 11, and 20 wt. %. The dielectric constant, dielectric loss, and saturation magnetization of the composites increase with the increasing CoFe2O4 content, being 13, 0.13, and 13 emu g−1, respectively, for x = 20. The change in the dielectric response (magnetodielectric effect (%)) is the highest among all the reported polymer-based composites for the x = 20 sample (4.2%), and on the contrary, the highest value of the magnetodielectric coefficient (γ) is higher on the x = 3 sample (0.015 emu−2 g2). Such features have large application potential in areas such as filters, magnetic field sensors and actuators, among others.

Magnetic contribution of Bi0.85La0.15FeO3 in (1−x)Bi0.85La0.15FeO3–(x)CoFe2O4 nanocomposite powders

In this work, a solid phase reaction method was used to fabricate (1−x)Bi0.85La0.15FeO3–xCoFe2O4 (x=0.1, 0.2, 0.3, 0.4) composite powders. X-ray diffraction patterns showed that no chemical reaction occurred between the separate Bi0.85La0.15FeO3 and CoFe2O4 phases and indicated that the powder samples had two distinct phases with a CoFe2O4 spinel phase and a Bi0.85La0.15FeO3 perovskite phase. The average crystallite sizes of the Bi0.85La0.15FeO3 in the composite powder were almost unchanged as the CoFe2O4 content was increased. By comparing the experimental and theoretical values for the magnetization, we found that the Bi0.85La0.15FeO3 phase contributed to the magnetization of the composite powders. In addition, it also provides a new way to prove the existence of magnetoelectric coupling in the sample.

Waterborne polyurethane-silanized CoFe2O4-acrylate magnetic pressure-sensitive adhesive

ABSTRACTA novel waterborne polyurethane-silanized CoFe2O-acrylate magnetic pressure-sensitive adhesive was prepared. With the increase of PU content, gel content, swelling capability, and SAFT increased, and fracture energy increased first, then decreased. The T-peeling strength increased from 8.93 to 19.07 N · m−1, tack force increased from No.3 to No.10, while shear resistance increased from 35 to 72 h, and then they decreased. Two empirical models: WA = 90.46 + 125.04[PU]-319.96[PU]2 and T = 9.09 + 96.07[PU]-235.11[PU]2, were obtained. With the increase of CoFe2O4 content, the saturation magnetization increased from 5.5 to 14.2 emu · g−1, and remanence increased from 1.7 to 3.7 emu · g−1, while coercivity decreased from 875 to 763 Oe.

Fabrication and application of magnetic starch-based activated hierarchical porous carbon spheres for the efficient removal of dyes from water

A novel and facile preparation of activated hierarchical porous carbon spheres (AHPCS) with high surface area and developed pore structure from corn starch, a new precursor of carbon materials, via enzymolysis, carbonization and KOH activation was presented in this investigations, and AHPCS was then loaded with CoFe2O4 to fabricate magnetic AHPCS. Results showed that the composites had good magnetic properties and morphology, and the CoFe2O4 were mainly distributed in the macroporous. The saturation magnetization (Ms) increased with the CoFe2O4 content, while the surface area and pore volume decreased. The sample-3 (CoFe2O4:AHPCS = 1:75) possessed the surface area of 2110.48 (close to 2711.19 m2 g−1 of AHPCS) and Ms of 11.91 emu·g−1, which were sufficient for magnetic separation in wastewater treatment. More than 97% methylene blue could be adsorbed in 5 min, and CoFe2O4/AHPCS composites could be separated from the solution easily by an outer magnet.

The effect of nanosized CoFe2O4 addition on the magnetic properties of GdBa2Cu3O7-δ using AC magnetic susceptibility measurements

Superconductor samples of type (CoFe2O4)xGdBa2Cu3O7-δ (0≤x≤0.1) were synthesized by the conventional solid-state reaction technique, whereas nanosized CoFe2O4 was prepared by co-precipitation method with grain size of about 8.5 nm. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE). The temperature dependence of real (χ') and imaginary (χʺ) components of AC magnetic susceptibility (ACMS) at different magnetic field amplitude (3–15 Oe) was investigated. The analysis of the temperature dependence of ACMS was performed using Bean critical state model. The values of the critical current density J c at T > T p (T p is the inter-granular loss peak temperature) were calculated as a function of magnetic field and nanosized CoFe2O4 content. It was found that the low nanosized CoFe2O4 addition content (x = 0.01) improves the critical current density J c of Gd-123 superconducting phase. The observed variation of J c with temperature indicated that the weak links are changed from superconductor–normal metal–superconductor (SNS) for free sample to superconductor–insulator–superconductor (SIS) type of junctions for samples added with nanosized CoFe2O4 of x > 0.01. We also discussed the experimental results in the framework of the critical state model to estimate the effective volume fraction of the grains f g using Cole–Cole plots.

Magnetic properties of sintered SrFe12O19–CoFe2O4 nanocomposites with exchange coupling

Two series of nanocomposite ferrites sintered at 700 °C and 900 °C, respectively, were prepared using SrFe12O19 and CoFe2O4 nanopowders obtained via a hydrothermal procedure. For the SrFe12O19/CoFe2O4 ferrites with a mass ratio ranging from 3:1 to 1:3, all the specimens exhibit a typical single-phase magnetic behavior, suggesting the existence of exchange coupling. Compared with single-phase SrFe12O19, after the emergence of exchange coupling, the saturation magnetization of composites increases markedly from 59.2 (700 °C) and 64.7 emu/g (900 °C) to 72.4 and 73.7 emu/g with the increase of CoFe2O4 content, respectively, accompanied with a relatively small decrease of coercivity from 173.1 (700 °C) and 232.8 kA/m (900 °C) to 141.7 and 169.2 kA/m, respectively. It is also found that in sintered CoFe2O4/SrFe12O19 composite ferrites of single-phase magnetic behavior with a mass ratio of SrFe12O19 (Rs) from 2% to 10% (with steps of 2%) of the CoFe2O4 mass, a dramatic enhancement of coercivity up to 93% (Rs = 10%, 900 °C) is obtained if compared with the single-phase CoFe2O4 ferrite, though accompanied with a maximum drop of saturation magnetization up to 9.6% (Rs = 10%, 900 °C). The enhancement of coercivity is ascribed to the pinning from SrFe12O19 and the exchange coupling between CoFe2O4 and SrFe12O19 ferrites. Though it may reduce the coercivity of magnetically hard phase, the exchange coupling could also be used to enhance the coercivity of magnetically soft phase.

Excess Conductivity Study in Nano-CoFe2O4-Added YBa2Cu3O7−d and Y3Ba5Cu8O18±x Superconductors

We report electrical conductivity fluctuation analyses on YBa2Cu3O7−d (noted Y-123) and Y3Ba5Cu8O18±x (noted Y-358) polycrystalline samples added with nano-sized ferrite cobalt (CoFe2O4) particles. Phases and microstructure have been systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations show that the grain size is reduced with increasing the content of CoFe2O4 in the yttrium-based superconductor (YBCO) matrix The temperature dependence of electrical resistivity ρ(T) has been measured and the effect of addition of magnetic CoFe2O4 in the paraconductivity region has been reported. The thermodynamic fluctuation is obtained by analyzing the excess of conductivity on the basis of the Aslamazov–Larkin theory. The coherence length, the effective layer thickness, critical magnetic fields, and critical current density are estimated. Superconducting parameters are affected by the nanoparticle addition, and results are discussed in relevance to the structural and microstructure differences between Y-123 and Y-358.

Synthesis and magnetoelectric effect of composites with CoFe2O4-epoxy embedded in 3–1 type porous PZT ceramics

Three-phase magnetoelectric (ME) composites of lead zirconate titanate (PZT)/cobalt ferrite CoFe2O4 (CFO)/epoxy were synthesized in sequence by a tert-butyl alcohol (TBA)-based freeze-casting technique, a chemical solution deposition method, and an impregnation process. The novel pseudo 3–0–1 type composite structure with a high content of CFO was examined using SEM and XRD. The composites showed not only stable and excellent dielectric behavior in a wide frequency range, but also good ferroelectricity and ferromagneticity at the same time, as can be seen from the typical electrical and magnetic hysteresis loops. The ME effect of the resultant 3–0–1 type ferroelectric/ferromagnet/polymer composites was found to be significantly dependent on the content of PZT and CFO. The maximum ME coefficient of 2.2mV/cmOe was observed when the PZT volume fraction is 0.5 and CFO mass fraction is 0.2. This synthesis route we proposed provides a new connectivity type of ME composite and shows potential applications in sensors and transducers.

Single-crystal octahedral CoFe2O4 nanoparticles loaded on carbon balls as a lightweight microwave absorbent

Since electromagnetic pollution is becoming more and more serious, the lightweight and highly efficient microwave absorbents are urgently needed to absorb unwanted electromagnetic microwaves. In this work, single-crystal octahedral CoFe2O4 nanoparticles with the diameter of about 20–25nm were successfully incorporated into the porous carbon balls (CB) via a one-step hydrothermal method. The incorporation of the CoFe2O4 nanoparticles into CB reduced the dielectric loss and increased the magnetic loss, resulting in better impedance matching. When the CoFe2O4 content in CoFe2O4/CB composites was 10wt.%, the minimum reflection loss (RL) was as low as −37.2dB, and the frequency band of RL below −10dB was 12.9–17.1GHz obtained with 1.5mm thickness. This excellent microwave absorption performance was much better than that of the pure octahedral CoFe2O4 nanoparticles, CB, and CoFe2O4/CB composites with CoFe2O4 content of 8.5wt.%. Owing to the low density of 1.1–1.2g/cm3 and good microwave absorption, the CoFe2O4/CB composite can meet the multiple requirements of microwave absorbent.

Characterization of Co-Modified <i>γ</i>-Fe<sub>2</sub>O<sub>3 </sub>Based Composite Nanoparticles

During the synthesis of γ-Fe2O3 nanoparticles using a chemically-induced transition in a FeCl2 solution, Co-surface modification was attempted by adding Co (NO3)2 and NaOH to the solution. The magnetization behaviors, morphologies, crystal structure, and chemical compositions of the as-prepared samples were characterized using vibrating sample magnetometry, transmission electron microscopy, X-ray diffractometry, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The as-prepared particles consisted of γ-Fe2O3/CoFe2O4 composite crystallite and a CoCl2·6H2O coating. The molar, mass and volume ratios of the phases were estimated from the characterization results for each sample. The Co-modified γ-Fe2O3 nanoparticles’ anisotropic constant is approximately 1.48×10-1 J/cm3. Their coercivity depends on the size of composite crystallites, which is based on the γ-Fe2O3/CoFe2O4 content rather than the Co content.

Dielectric and magnetic properties of xCoFe2O4–(1 − x)[0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3] composites

xCoFe2O4–(1−x)(0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3) composites with x=0.1, 0.2, 0.3 and 0.4 have been synthesized by solid state reaction method. X-ray diffraction analysis and field emission secondary electron microscopy have been used for structural and morphological analysis, respectively. The spinel CoFe2O4 and perovskite 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 phase could be identified in the composites. Two anomalies in dielectric constant have been identified: first one is close to ferroelectric to paraelectric phase transition of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 ceramic and the other lies near the magnetic transition temperature of CoFe2O4. There is an increase in magnetocapacitance and saturation magnetization of the composites at room temperature with increase in CoFe2O4 content. The magnetoelectric coupling coefficient (γ) was approximated by Δϵ∼γM2 relation. The optical band gap energy of the composites decreases with increase in CoFe2O4 content.

Enhanced magnetodielectric effect and optical property of lead-free multiferroic (1 − x)(Bi0.5Na0.5)TiO3/xCoFe2O4 composites

(1 − x)(Bi0.5Na0.5)TiO3/xCoFe2O4 composites with x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 were synthesized by solid state reaction method. Presence of distinct ferroelectric (Bi0.5Na0.5)TiO3 and ferrite CoFe2O4 phases in the prepared composites have been confirmed by the X-ray diffraction analysis and field emission scanning electron micrographs. The variation of dielectric constant with temperature for these prepared composites show an anomaly near antiferroelectric to paraelectric phase transition temperature (∼345 °C) of pure (Bi0.5Na0.5)TiO3 ceramics. The dielectric constant of the composites at low frequency range decreases with increase in CoFe2O4 content up to x = 0.3 but increases for x = 0.4 and x = 0.5. The value of remnant magnetization for 10 and 50% CoFe2O4 are 2 and 14 emu g−1 respectively. The maximum value of magnetocapacitance was found to be ∼4.37% for 50% CoFe2O4 content. Increase in CoFe2O4 content in composites shifts the optical band gap of (Bi0.5Na0.5)TiO3 towards lower energy side.

Magnetic properties and methylene blue adsorptive performance of CoFe2O4/activated carbon nanocomposites

Owing to the unique microporous structure and high specific surface area, activated carbon (AC) could act as a good carrier for functional materials. In this paper, CoFe2O4/AC nanocomposites were prepared by a facile hydrothermal method for the adsorption of dyes in wastewater. The results indicated that CoFe2O4 nanoparticles presented the spinel structure and existed in the pores of AC. The saturation magnetization (Ms) increased with the CoFe2O4 content, while the surface area and pore volume decreased. For the larger magnetic moment, very few CoFe2O4 were needed to maintain the higher surface area of CoFe2O4/AC nanocomposites. The sample-5 (CoFe2O4:C = 1:200) possessed the surface area of 1096.85 m2 g−1 (close to 1243.35 m2 g−1 of AC) and Ms of 5.11 emu g−1, which were sufficient for magnetic separation in wastewater treatment. 99% methylene blue could be adsorbed in 50 min, and then the CoFe2O4/AC nanocomposites could be separated from the solution easily by an outer magnet.

Comparative study of nano-sized particles CoFe2O4 effects on superconducting properties of Y-123 and Y-358

The effects of nano-sized CoFe2O4 particles (10nm) addition on the structural and the normal state resistivity of YBa2Cu3O7 (noted Y-123) and Y3Ba5Cu8O18 (noted Y-358) polycrystalline were systematically studied. Samples were synthesized in oxygen atmosphere using a standard solid state reaction technique by adding CoFe2O4 up to 2wt%. Phases, microstructure and superconductivity have been systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical measurements ρ(T). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations reveal that the grain size is reduced with increasing the content of CoFe2O4. The measurements for the resistivity dependence of temperature show that the depression in superconducting temperature is more pronounced for CoFe2O4 addition in Y-358 compound than in Y-123 one. These results may be attributed to the existence of much more disorder due to a greater number of Cu sites to be substituted by Fe and Co in Y-358 compared to Y-123.

Preparation and Dielectric Characteristics of Semitransparent CoFe2O4–P(VDF-TrFE) Nanocomposite Films

Polymer–ceramic nanocomposites play an important role in embedded capacitors. However, polymer–ceramic dielectrics are limited for commercial applications due to their low transmittance, poor adhesion, and poor thermal stress reliability at high filler loadings. Thus, materials design and processing is critical to prepare films with improved dielectric properties and low filler loading. In this work, we use a spin coating-assisted method to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]–CoFe2O4 (CFO) nanocomposite films. Magnetic CFO nanoparticles in the size range of 10 nm to 40 nm were successfully synthesized using a hydrothermal process. The dispersion of the nanoparticles, the dielectric properties, and the transmittance of the nanocomposite films were studied. The dielectric constant of the nanocomposite films increased by about 45% over the frequency range of 100 Hz to 1 MHz, compared with that of pristine P(VDF-TrFE) film. Optical measurements indicated that the transmittance of the films remains above 60% in the visible range, indicating a relatively low content of CFO in the polymer matrix. Our experimental results suggest that spin coating-assisted dispersion may be a promising route to fabricate dielectric polymer–ceramic nanocomposite films of controllable thickness.

SYNTHESIS OF MAGNETIC SBA-15 AND Fe–SBA-15 MESOPOROUS NANOCOMPOSITES WITH COBALT FERRITES

A new nanocomposite based on SBA-15 mesoporous materials combined with Fe2O3 and CoFe2O4 nanoparticles was prepared via sol–gel growth. The nanostructures and magnetic properties of the SBA-15 nanocomposite were investigated by X-ray diffraction topography, high resolution transmission electron microscopy, and vibrating sample magnetometer. Results indicate that α- Fe2O3 nanoparticles are present in the frame or micropores of SBA-15 (denoted as Fe –SBA-15 below) and that CoFe2O4 nanoparticles are confined in the mesoporous channels of Fe –SBA-15. Our results also reveal that the addition of CoFe2O4 and α- Fe2O3 magnetic nanoparticles critically affects their magnetic properties. The saturation magnetization of the SBA-15 nanocomposite is attributed to ferrimagnetic CoFe2O4 nanoparticles and antiferromagnetic α- Fe2O3 nanoparticles, whereas the coercivity increases with the content of CoFe2O4 . Moreover, the presence of the couple exchange interaction between the magnetic nanoparticles is confirmed, which can enhance the magnetic properties of the SBA-15 nanocomposite.

Fabrication of the Cobalt Ferrite/Modified Sodium Bismuth Titanate 0-3 Multiferroic Composites via Diffusion-blocking

通过溶胶-凝胶工艺在CoFe 2 O 4 (简称CFO)粉体表面包覆二氧化锆陶瓷层来阻挡烧结过程中铁磁相与铁电相之间的离子扩散. 包覆后的CFO与0.92(Bi 0.5 Na 0.5 )TiO3-0.02(Bi 0.5 K 0.5 )TO 3 -0.06BaTiO 3 (简称BNBT) 陶瓷粉体分别按照 x CFO/(1- x ) BNKLABT (质量分数 x = 0.05、0.10、0.15、0.20、0.25、0.30)混合均匀, 并用聚乙烯醇为粘结剂模压成圆片; 再经过1050℃烧结制备了铁磁/铁电0-3型复合材料. XRD分析表明: 二氧化锆在高温烧结过程中对离子扩散具有良好的阻挡作用. 复合陶瓷的耐击穿电压大于75kV/cm. 测量结果表明: 复合陶瓷的压电应变常数、机电耦合系数、介电常数和剩余极化随CFO含量的增加而降低; 磁电耦合系数、介电损耗随CFO含量的增加而有所增大. -35mm×1.5mm的复合陶瓷样品( x =0.05)在谐振频率(90kHz)和199kA/m 偏置磁场下的磁电系数为1.39V/A.

Preparation and electromagnetic wave absorption of flower-like ZnO-CoFe2 O4 nanotube bundles composites

Flower-like ZnO-CoFe2O4 nanotube bundle composites are prepared via two-step crystal growth process in water solution at 90 ℃, the wall thicknesses of the ZnO nanotubes are all about 60 nm, inner diameters of the tubes are all about 350 nm, ZnO nanotubes have been coated with CoFe2O4 nanoparticles, and the sizes of CoFe2O4 nanoparticles are below 40 nm. The thickness of CoFe2O4 coating layer increases with the increase of the content of CoFe2O4 in ZnO-CoFe2O4 composites. By using Flower-like ZnO,flower-like ZnO-CoFe2O4 nanotube bundles and CoFe2O4 nanoparticles as absorbents, and phenolic resin as the binder, their electromagnetic wave absorption properties are investigated, and the results show that the microwave wave absorbing performance is evidently improved compared with that of ZnO nanotube bundles and CoFe2O4 particles. When the content of ZnO is 60%, the maximum reflection loss is 28.3 dB.

Electrophoretic Deposition of CoFe2O4 Nanograins Dispersed in a Laser Ablated BaTiO3 Matrix

Thin film nanocomposites composed by CoFe2O4 grains, deposited by electrophoresis, and subsequently covered by a laser ablation deposited BaTiO3 layer, were prepared with different cobalt ferrite concentrations (x). The cobalt ferrite phase was under a compressive strain that relaxed as the CoFe2O4 concentration increased. Consequently, a blueshift of the Raman peaks of CoFe2O4 was observed, that decreased with increasing x. The dielectric permittivity of the films was found to decrease with increasing cobalt ferrite concentration, due to the decrease of the barium titanate layer grain size with increasing CoFe2O4 content in the films.