Magnetic and dielectric properties of Zn substituted cobalt oxide nanoparticles

Zinc-substituted cobalt oxide nanoparticles (Zn_xCo_3-xO_4, 0 ≤ x ≤ 0.5) were produced by microwave refluxing technique. The structural, microstructural and magnetic properties of these samples were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and magnetic property measurement system (MPMS) respectively. XRD and TEM analyses confirmed the single phase nature for all the samples. Rietveld analysis of the samples further confirmed the substitution of Zn-ions into the Co₃O₄ lattice. The chemical states of the elements were studied using X-ray photoelectron spectroscopy (XPS), which suggest the presence of Zn²⁺, Co²⁺, and Co³⁺ ions in the samples. The maximum saturation magnetization (M_S) values of 0.33 Am²/kg was obtained for x = 0.01 sample, and then it continuously reduced with increased Zn content. The dielectric property of the samples was studied in the frequency range of 40 Hz–110 MHz. The samples x = 0.05 and 0.5 displayed the lowest conductivity due to the narrow size distribution of grains.     

Magnetic and dielectric properties of natural rubber and polyurethane composites filled with cobalt ferrite

Abstract

Cobalt ferrite (CoFe₂O₄) powders synthesised by sol–gel techniques were incorporated into natural rubber (NR) and polyurethane (PU) by two-roll milling at different loadings from 0 to 45 phr. In either NR or PU composites, the magnetisations were proportional to the CoFe₂O₄ loading, but the coercive field remained rather insensitive to the loading. The frequency response from 1 MHz to 1 GHz revealed that the real part of the magnetic permeability increased significantly only in the case of 45 phr CoFe₂O₄, while the imaginary part was modest in both NR and PU composites. In contrast, the electrical permittivity of CoFe₂O₄–PU was larger than that of CoFe₂O₄–NR composites, and both parts at 100 MHz had linear variations with the loading, in agreement with Wagner’s equation.     

Chromium incorporated nanocrystalline cobalt ferrite synthesized by combustion method: Effect of fuel and temperature

Nanocrystalline CoCrFeO₄ samples were prepared by Cost effective and low temperature combustion method using different fuels as glycine, urea and polyvinyl alcohol and the effect of temperature on their physical properties has been studied. The thermal study of the precursor gels was done by using Thermogravimetric and Differential thermal analysis (TG-DTA). Occurrence of the cubic spinel phase for the samples was confirmed by the Rietveld analysis of X-ray diffraction (XRD) data. The refinement results also confirm that the cationic distribution over the tetrahedral and octahedral sites in the spinel lattice of samples is partially inverse. The magnetic studies indicate a superparamagnetic behaviour, showing an increase in the blocking temperatures with the particle size in case of all fuels. All the samples showed ferromagnetic behaviour and the nanoparticles prepared by using glycine as a fuel were found to have largest crystallite size and relatively stronger A–O–B interaction compared to others. Magnetization measurements exhibit non-collinear ferrimagnetic structure for the samples.     

Magnetic and antimicrobial properties of cobalt-zinc ferrite nanoparticles synthesized by citrate-gel method

The cobalt-zinc ferrite (CZF) nanomaterials were prepared by citrate-gel method, and further calcined at 600°C. The single-phase cubic spinel structure of CZF was confirmed using the X-ray diffraction pattern. The average crystallite size was found to be in the range of 22-29 nm. The surface morphology was examined using the scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The average particle size of Co_0.6Zn_0.4Fe₂O₄ was determined to be 19 nm using TEM study which is supporting the average crystallite size measured from the X-ray diffraction studies. The Fourier-transform infrared spectra revealed the two strong absorption bands in the series of ferrites between 4500 and 500 cm⁻¹ and these are responsible for the characteristic of spinel ferrites. The presence of elements Cu, Zn, and Co of CZF was confirmed by the elemental spectral signals of energy dispersive spectroscopy. At room temperature, the magnetic measurements of pure ZnFe₂O₄ and Co_0.6Zn_0.4Fe₂O₄ were evaluated based on hysteresis curves (M-H curves). The results expressed that the addition of nonmagnetic Zn²⁺ ions increases the magnetic behavior in the mixed CZF samples. The antimicrobial activity of the ZnFe₂O₄ and Co_0.6Zn_0.4Fe₂O₄ nanoferrites was tested against harmful microbes.     

Structural,electrical, and magnetic properties of Zn substituted magnesium ferrite

Zinc substituted magnesium (Mg–Zn) ferrites with the general formula Mg_1−xZn_xFe₂O₄ (x=0.00, 0.25, 0.50, 0.75, and 1.00) were prepared using the solution combustion route. The dried powder after calcination (700 °C for 2 h) was compacted and sintered at 1050 °C for 3 h. The structural, morphological, dielectric and magnetic properties of the sintered ferrites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance spectroscopy, and vibration sample magnetometry (VSM). The XRD analysis of sintered samples confirmed that the expected spinel cubic phase was formed for all samples. The crystallite sizes evaluated using Scherre's formula were found to be in the range of 47–80 nm. SEM analysis showed homogeneous grains with a polyhedral structure. The electrical conductivity increased with increasing frequency, which is normal dielectric behavior for such materials. The dielectric constant, dielectric loss tangent, and AC conductivity were found to be lowest for x=0.50. The VSM results showed that the zinc concentration had a significant influence on the saturation magnetization and coercivity.     

Diffusion of cobalt in diamond films synthesized by combustion flame method

It is well known that Cobalt (Co) plays an important role during diamond deposition on cemented carbide substrates (WC). The presence of cobalt on the substrate lead to decrease adhesion and increase the formation of non-diamond compounds phases. However, the diffusion phenomenon of cobalt in diamond coatings is not well understood.We have carried out a detailed study to investigate the diffusion of cobalt during the nucleation and growth of diamond on WC-Co substrate by combustion-flame method, and the influence of it on the structure and quality of the diamond coatings. At high substrate temperature T_s>800 °C, ball-sharp of cobalt with a ball size about 0.7 μm was observed on the top surface of diamond coatings (thickness >50 μm). The constraints in the coating are very high, the Raman peak appearance at 1341.1 cm⁻¹. At relatively low substrate temperature, T_s is about 550 °C, ball sharp of cobalt was not observed by MEB but a lot of cobalt particles dissolution carbon films were detected by EDX.Based on the above results, the influence of cobalt on the structure, the quality and the constraints in the diamond films are discussed, a model suggesting the nucleation and growth mechanisms of diamond, to explain the cobalt diffusion in diamond films, is presented.     

Structural and ferroelectric properties of hafnium substituted BiFeO3 multiferroics synthesized via auto combustion technique

A series of BiFe_1-xHf_(3/4)xO₃ ( 0%, 5%, 10%, 15% and 20%) nanoparticles were synthesized by simple auto combustion technique using citric acid as a fuel. Thermogravimetric (TGA), differential thermogravimetric (DTA), structural, magnetic, dielectric and ferroelectric analyses were investigated. Thermogravimetric analysis provides information of temperature at which phase develops (600?°C). DTA predicts ferroelectric to paraelectric transformation temperature which is found to be 822?°C. X-ray diffraction (XRD) results confirm formation of distorted rhombohedral structure for all compositions along with few traces of Bi₂₅FeO₄₀. The tolerance factor is increased from 0.845 to 0.853 due to larger ionic radius of Hf⁴⁺ substitution on Fe site. Crystallite size (D) is found in the range of 24.2–30.48?nm. Saturation magnetization (Ms) is increased to 16 times and remanent magnetization (Mr) is increased to 8 times than that of pure BiFeO₃. This increment in magnetic parameters is due to reduction of oxygen vacancies, small crystalline size (less than 62?nm), structural distortion and unbalancing condition for antiferromagnetic magnetic moments of Fe³⁺ ions. Dielectric parameters depict decrement behavior with increasing of applied field up to 3?GHz. For Fe_1-xHf_(3/4)xO₃, lower value of dielectric permittivity for all compositions is due to reduction of polarization and less growth of grains but more growth of grain boundaries because of mismatching of Hf and Fe³⁺ ions. P-E hysteresis loop changes from round shape to elliptical shape and it confirms less lossy nature of ferroelectric loops. Higher values of Ms as well as Mr but lower values of dielectric constant as well as remanent polarization for these nanoparticles make them useful for MeRAM (magnetoelectric random access memory) and high resonant applications.     

Microwave-assisted solution synthesis,microwave sintering and magnetic properties of cobalt ferrite

A simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of nanocrystalline cobalt ferrite powders from commercially-available Fe(NO₃)₃?9H₂O, Co(NO₃)₂?6H₂O, ammonium hydroxide, and tetrapropylammonium hydroxide (TPAH). The synthesis was conducted in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized by XRD, FE-SEM, TEM, and HR-TEM. After a systematic study of the influence of the microwave variables (temperature, reaction time and nature of the bases), highly crystalline CoFe₂O₄ nanoparticles with a high uniformity in morphology and size, were directly obtained by heating at 130?°C for 20?min using the base TPAH. Dense ceramics of cobalt ferrite were prepared by non-conventional, microwave sintering of synthesized nanopowders at temperatures of 850–900?°C. The magnetic properties of both the nanopowders and the sintered specimens were determined in order to establish their feasibility as a permanent magnet.     

Structural,dielectric, electric and magnetic properties of magnesium substituted lithium nanoferrites

Magnesium substituted Li-ferrites nanoparticles with chemical composition Li_0.5-0.5xMg_xFe_2.5-0.5xO₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1) synthesized by sol-gel auto combustion method. Synthesized materials were sintered at 600 °C for 4 h in the air and heated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) techniques. Rietveld refinement of XRD patterns confirmed the formation of the spinel structure where the lattice constant varied with the increase of Mg content. The crystallite size of magnesium-substituted lithium ferrites was calculated using Scherrer's equation and showed slight changes while the W-H plot shows more changes. The electrical conductivity and activation energy of Mg-substituted lithium ferrite were strongly affected by Mg content and by which they appear to confirm to semiconductor nature. The paramagnetic transition to ferrite was confirmed by the change in the Arrhenius plot, which showed a large variation between two regions that differ in the values of the activation energy, where the values of activation energies in the ferrite region were greater than those that appeared in the para region, as well as the variation between the activation energy values in the non-substituted lithium ferrite. The dielectric parameters such as the real part of the dielectric constant and loss tangent of the samples were analyzed in the range of 50 Hz to 5 MHz at room temperature, 100, 300, and 500 °C. Curie's temperature showed a decrease with the increase in Mg content. Hysteresis loops were measured using a vibrating sample magnetometer (VSM) where both the temperature and the applied magnetic field were changed. The FC result of Li_0.5-0.5xMg_xFe_2.5-0.5xO₄ (x = 0.2, 0.4, and 0.6) is almost flat below T_B which demonstrates that the Li–Mg nano ferrites show a super-spin glass behaviour.     

Structural,magnetic and electrical properties along with antifungal activity & adsorption ability of cobalt doped manganese ferrite nanoparticles synthesized using combustion route

Ultrafine powders of Cobalt doped manganese ferrite with elemental composition Mn_1-xCo_xFe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) were synthesized using combustion method. The formation of the pure cubic spinel phase of ferrite structure was confirmed using X-ray diffraction and Fourier transform infrared spectroscopy. Structural parameters such as lattice constant, X-ray density, mass density, porosity, and cell volume were seen to be greatly influenced by cobalt doping. The surface morphology of the nanocrystalline samples was studied using a scanning electron microscope. The particle size distribution was determined using a Transmission electron microscope and nanograins of the samples were found to have dimensions in the range 15 nm–30 nm. It also showed its dependence on the extent of cobalt inclusion. Variation of magnetization and magnetic moment as a function of magnetic field and temperature was investigated using a vibrating sample magnetometer (VSM). The parameters such as saturation magnetization ‘M_S’ and inversion temperature T_I were seen to depend upon Co⁺² concentration. The variation dielectric constant ‘Ԑ’ as a function of frequency was studied. Antifungal activity of these ferrite nanoparticles against Rhizopus fungi was also investigated at room temperature. The antifungal activity was seen to increase with increasing Co⁺² content in the manganese ferrite structure and hence cobalt doped manganese ferrites are proposed as a candidate material for industries manufacturing antifungal products. The adsorption studies were also investigated using Methylene dye as the adsorbate.     

Magnetic,magnetostrictive, and AC impedance properties of manganese substituted cobalt ferrites

In this study, we investigated the effects of substituting Mn³⁺ for some Fe³⁺ in spinel lattice on the structure, magnetic properties, magnetostriction behavior, and AC impedance characteristics of cobalt ferrites. The manganese substituted cobalt ferrites (Co–Mn ferrites), CoMn_xFe_2−xO₄, with x varied from 0 to 0.3 in 0.1 increments, were prepared by solid-state reaction. XRD examination confirmed that all sintered Co-based ferrites had a single-phase spinel structure. The average grain size, obtained from SEM micrographs, increased from 8.2 μm to 12.5 μm as the Mn content (x) increased from 0 to 0.3. Both the Curie temperature and coercivity of Co-based ferrites decreased with greater amounts of Mn, while the maximum magnetization (at H=6 kOe) of Mn-substituted cobalt ferrites was larger than that of the pure Co-ferrite. Magnetostrictive properties revealed that the pure Co-ferrite had the largest saturation magnetostriction (λ_S), about −167 ppm, and the CoMn_0.2Fe_1.8O₄ sample exhibited the highest strain sensitivity (|dλ_⊥/dH|_m) of 2.23×10⁻⁹ A⁻¹m among all as-prepared Co-based ferrites. In addition, AC impedance spectra analysis revealed that the real part (Z′) of the complex impedance of Co–Mn ferrites was lower than that of pure Co-ferrite in the low frequency region, and the Co-based ferrites exhibited semiconductor-like behavior.     

Magnetic and catalytic properties of copper ferrite nanopowders prepared by a microwave-induced combustion process

Copper ferrite nanopowders were successfully synthesized by a microwave-induced combustion process using copper nitrate, iron nitrate, and urea. The process only took a few minutes to obtain CuFe₂O₄ nanopowders. The resultant powders were investigated by XRD, SEM, VSM, and surface area measurement. The results revealed that the CuFe₂O₄ powders showed that the average particle size ranged from 300 to 600 nm. Also, it possessed a saturation magnetization of 21.16 emu/g, and an intrinsic coercive force of 600.84 Oe, whereas, upon annealing at 800 °C for 1 h. The CuFe₂O₄ powders specific surface area was 5.60 m²/g. Moreover, these copper ferrite magnetic nanopowders also acted as a catalyst for the oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethylhydrogenquinone and 2,3,5-trimethyl-1,4-benzoquinone for the first time. On the basis of experimental evidence, a rational reaction mechanism is proposed to explain the results satisfactorily.     

The influence of cationic surfactant CTAB on optical,dielectric and magnetic properties of cobalt ferrite nanoparticles

In the present work, the influence of cationic surfactant CTAB (cetyltrimethylammonium bromide) on size, shape and coalescence behaviour of cobalt ferrite nanoparticles (CFNPs) synthesized via hydrothermal method is reported. Pure CFNPs show no additional peaks, whereas α-Fe₂O₃ phase is observed in CTAB added CFNPs upon annealing. FT-IR analysis confirms the formation of M − O vibrational bands (metal -oxygen) at tetrahedral A-site and octahedral B-site for both samples. SEM observations reveal less agglomeration and smaller particle size for surfactant added CFNPs. Raman spectral study confirms the formation of cubic spinel structure and Raman active modes of CTAB added CFNPs. UV–Vis spectra indicate a decrease in the energy band gap with annealing. The dielectric constant of surfactant added CFNPs decreases with increasing applied frequencies for both real and imaginary, but ac conductivity increases with increasing frequencies. Two sextet patterns of Fe³⁺ trivalent ions from tetrahedral and octahedral sites are observed in Mössbauer spectra. VSM study indicate the ferrimagnetic nature of CTAB added CFNPs. The electrochemical analysis reveals the pseudocapacitive nature of working electrode prepared by CTAB added CFNPs.     

Structural and mechanical properties of nanograined magnesium ferrite produced by oxalate coprecipitation method

Magnesium ferrite (MgFe₂O₄) was prepared by simple low-cost oxalate coprecipitation method and characterized by XRD and SEM. The X-ray analysis confirmed the formation of a single-phase cubic spinel structure. The product revealed a non-uniform morphology and some certain extent of agglomeration. Crystallite size, texture coefficient, dislocation density, hopping length, and mechanical properties of the product are also reported.     

Microwave dielectric properties of Al-doped ZnO powders synthesized by coprecipitation method

Al-doped ZnO (AZO) powders with different Al concentrations were synthesized by coprecipitation method. Crystal structural and dielectric properties of the powders as a function of aluminum doping concentration as well as annealing temperature were investigated. The XRD results reveal that Al atoms are doped into ZnO lattice successfully and all the samples are polycrystalline with a hexagonal wurtzite structure. The real part (ε′) and imaginary part (ε″) of the complex permittivity of the powders were carried out by a vector network analyzer in the microwave frequency range of 8.2–12.4 GHz. The results show that the ε′ and ε″ of the doped ZnO powders increase with the doping content and both of them are higher than that of the pure one. For the AZO powder with 7 mol% Al, both ε′ and ε″ increase firstly and then decrease with increasing annealing temperature.     

一步烧结法合成镁铝尖晶石的研究与工业应用

以特级铝矾土生料、轻烧氧化镁粉等为原料,纸浆废液为结合剂,在1600℃煅烧3h,研究了活性Al2O3微粉、镁铝尖晶石粉、硼酸(H3BO3)、MgCl2.6H2O等对合成镁铝尖晶石体积密度的影响。结果表明,添加硼酸能有效提高合成尖晶石的体积密度,而且对工业生产成本增加有限,本试验的最佳加入量(质量分数)为1.5%。在不改变基本原料和工艺参数的情况下进行了工业试验,即将质量分数为1.5%的硼酸与矾土生料和轻烧镁粉共磨,然后加入适量纸浆废液混练并压球成型,干燥后在回转窑中于1700℃煅烧。结果表明,在矾土基合成镁铝尖晶石的生产工艺中,添加少量硼酸能促进合成尖晶石的烧结,提高合成尖晶石的体积密度和产品回收率,具有一定的应用价值。     

Solution properties of hydrophobically modified polyelectrolytes synthesized via solution and micellar copolymerization

Hydrophobically modified polyelectrolytes (HMPEs) were synthesized using sodium 2‐acrylamido‐2‐methyl‐propanesulfonate and N‐n‐dodecylacrylamide as monomers with the same feeding ratio via micellar and solution copolymerization. The effects of hydrophobic association and electrostatic interaction on the solution properties of the HMPEs were studied. Compared with HMPE obtained via solution copolymerization (s‐PAD), the hydrophobic interaction of HMPE obtained via micellar copolymerization (m‐PAD) is more obvious due to the micro‐blocky distribution of hydrophobic groups. The viscosity properties of m‐PAD in deionized water or brine follow well the scaling theory of polyelectrolytes. However, for s‐PAD, the concentration where zero‐shear viscosity (η₀) and solvent viscosity (η_s) follow η₀ ≈ 2η_s is more likely to be critical entanglement concentration (c_e) rather than critical overlap concentration (c*). It is suggested that modifying of the transition region from c* to c_e is valid and reasonable for s‐PAD. It is believed that the different solution properties of s‐PAD and m‐PAD should be attributed to the distributions of hydrophobic groups in the chains. Copyright © 2010 Society of Chemical Industry     

Magnetic and dielectric properties of barium ferrite fibers/poly(vinylidene fluoride) composite films

Barium ferrite fibers/poly(vinylidene fluoride) (BaFe₁₂O₁₉/PVDF) composite films were prepared from poly(vinylidene fluoride) (PVDF) resin with different weight percentages (1, 5, 10, 20, 30 wt%) of M-type barium ferrite fibers using N,N-dimethylformamide as a solvent. The structure and morphology of the BaFe₁₂O₁₉/PVDF composite films were characterized by scanning electron microscopy and X-ray diffraction. These results show that BaFe₁₂O₁₉ fibers with diameters around 1 μm and an aspect ratio (length/diameter) of about 50 are well dispersed in the PVDF resin and the dispersed fibers result in a structural change of the PVDF from α to β phase. Measurements of the magnetization of the composite films by using a vibrating sample magnetometer show that these BaFe₁₂O₁₉/PVDF composite films possess a hard magnetic characteristic. The specific saturation magnetization and dielectric loss increase with BaFe₁₂O₁₉ content, whereas the coercivity and dielectric constant of the composite films are less affected. These BaFe₁₂O₁₉/PVDF composite films can combine magnetic, dielectric, and mechanical properties of the BaFe₁₂O₁₉ and PVDF phases.