Enhanced structural,electromagnetic and absorption features of CoSm ferrite-metamaterial absorbers through synergistic effects

Currently, materials with outstanding absorption abilities, such as thin size, better absorbing power, and light weight are the need of industry to resolve the electromagnetic issues. However, the research on optimizing the composition of the material, microstructure and the structure of the absorber are also the important factors for enhancing the absorption features. A metamaterial microwave absorber (MMA) based on nano ferrites with desirable absorption peaks is proposed and simulated. Sol-gel auto combustion route is used to prepare the nanosized Sm doped Co ferrite with Co_1+xSm_xFe_2-2xO₄ at x = 0.00, 0.03, 0.06, 0.09, respectively. XRD, VSM, FESEM, and VNA were employed to evaluate the structural, magnetic, morphological, and dielectric features. Rietveld refinement of the XRD patterns of samples was evaluated. Refined parameters show the spinel phase's emergence and the Fe₂O₃ phase. Grain size and crystallite size were increased with Sm doping in Co ferrite. Electromagnetic studies depicted that the highest dielectric constant value was found at x = 0.09 and the minimum value at x = 0.03, respectively. Sm doped Co ferrite at x = 0.09 depicted high Q values at higher frequencies. The coercivity values first decreased and then increased. All samples exhibit variations in coercivity and magneto-crystalline anisotropy constant. This variation was attributed to the super-exchange interactions and strong LS coupling of the cations. The multiple absorption peaks are attained for TE-polarization, and the absorptivity is considerably improved for x = 0.09. The proposed absorber simulated from CST depicted the absorption peaks of the S-band and C-band of the microwave regime. The synergistic effects among the metamaterial and ferrite layers may enhance the absorption feature and would be useful for satellite communication applications.     

Impact of Co doping on physical,structural, microstructural and magnetic features of MgZn nanoferrites for high frequency applications

Cobalt (Co) doped MgZn spinel nanoferrites with composition Mg_0.5Zn_0.5Co_x Fe_2-xO₄ at x = 0.0, 0.10, 0.20, 0.30, 0.40, 0.50 were prepared using sol-gel auto ignition method. The characterizations techniques such as FESEM, FTIR, XRD and VSM were used to determine the morphology, force constants, phase, structure and magnetic features of the samples. Lattice parameters, FWHM, d-spacing, crystallite size, micro strains and volume were investigated using high score plus software. Materials analysis using diffraction (MAUD) software was also used to study the Rietveld refinement properties of the Co doped MgZn ferrites. Physical properties such as porosity, X-ray and bulk density were also determined. Force constants of their respective absorption bands were calculated from FTIR of the Co doped MgZn nanoferrites. Single phase structure with cubic phase were observed for MgZn and Co doped MgZn at x = 0.0 whereas second phase was observed at higher Co concentrations respectively. FESEM show regular shape of the particles at low Co concentrations whereas agglomerations were observed at higher Co concentrations respectively. The magnetic properties of the Co doped MgZn ferrites were also investigated from VSM study. Magnetic remanence, coercivity, initial permeability, saturation magnetization, Bohr magneton and anisotropy constant were determined from VSM analysis. The coercivity, saturation magnetization, remanence, anisotropy constant and initial permeability were enhanced with the doping of ‘Co’ in MgZn nanoferrites. Response of the Co doped MgZn nanoferrites at high frequency regime was also evaluated. It can be seen that the response from all the Co doped MgZn nanoferrites was 2.84 GHz–5.96 GHz respectively and suggested the use of these nanoferrites for the operation of nanodevices in the X-band high frequency regime.     

Synthesis of dysprosium/Mn–Cu ferrite binary nanocomposite: Analysis of structural,morphological, dielectric,and optomagnetic properties

Manganese–copper ferrite (MCFO) and dysprosium (Dy)-doped manganese–copper ferrite nanocomposites (Mn_0.5Cu_0.5Dy_xFe_2−xO₄) (x = 0, 0.05, 0.10, and 0.15) were synthesized by sonochemical method. Crystal structure and the structural parameters of the MCFO were analyzed based on the doping concentration of Dy ion. It was observed that the average crystalline size of the synthesized nanocomposite decreases when the concentration of Dy increases. The existing spherical surface morphology of the MCFO and Dy-doped MCFO nanocomposites were obtained through scanning electron microscopy. In the UV spectrum, the pristine MCFO sample showed an absorbance peak at 743 nm whereas the absorbance values of Dy-doped ferrite nanocomposite considerably shifted (blue) toward a lower wavelength (231–222 nm). The dielectric parameters of all ferrite nanocomposites were studied in the frequency range of 100 Hz to 5 MHz. The dielectric spectrum revealed that dielectric constant and loss tangent decreased with increased doping concentration of Dy ion. The saturation magnetization also changed with Dy doping in MCFO. The impact of Dy on manganese–copper ferrite changed the optical, dielectric and magnetic properties of the prepared binary ferrite nanocomposite, which can be used for microwave-absorbing material applications.     

Effect of neodymium ion on the structural,electrical and magnetic properties of nanocrystalline nickel ferrites

NiNd_xFe_2-xO₄ nanoferrites with different compositions of x?=?0.01, 0.03, 0.05, 0.07 and 0.09 were prepared using the sonochemical method. The structural, optical and morphological properties of the prepared nanoferrites were characterized by X-ray diffraction, ultra violet-diffuse reflectance spectroscopy, scanning electron microscopy and X-ray fluorescence techniques. The X-ray diffraction analysis of the prepared nanoferrites confirmed the presence of a cubic spinel structure. The average crystallite sizes of the prepared nanoferrites were 52, 49, 46, 44 and 40?nm for x?=?0.01, 0.03, 0.05, 0.07 and 0.09, respectively. The particle size of the prepared NiNd_xFe_2-xO₄ nanoferrites was in the range 60–40?nm. The dielectric parameters ranged from 2.9?GHz to 5.6?GHz. Decrease in the dielectric constant was observed with an increase in Nd³⁺ ions in the prepared NiNd_xFe_2-xO₄ nanoferrites. However, a reverse trend was observed in the dielectric loss. An impedance analysis of the prepared nanoferrites was carried out to explore the pseudo-capacitance behavior. The saturation magnetization and remnant magnetization values of the prepared nanoferrites decreased with an increase in the concentration of Nd³⁺ ions in NiNd_xFe_2-xO₄ nanoferrites.     

Preparations and characterizations of Ca doped Ni–Mg–Mn nanocrystalline ferrites for switching field high-frequency applications

Ca-doped Ni–Mg–Mn spinel ferrites with compositions of Ni_0·5Mg_0·3Mn_0.2Ca_xFe_2-xO₄ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared via sol-gel auto-ignition technique. TGA/DTA, FTIR, XRD, FESEM, and VSM were employed to evaluate the thermal, spectral, structural, morphological, and magnetic features of Ca-doped Ni–Mg–Mn spinel ferrites. TGA/DTA curves show the weight loss in the sample. This weight loss was attributed to the oxidation and decomposition of the sample contents at a temperature of 500 °C. XRD reveals a single-phase structure of the Ni–Mg–Mn nano ferrites. A single-phase orthorhombic structure was confirmed for Ca-doped Ni–Mg–Mn ferrites. Structural parameters such as lattice parameter, ‘da’, ‘db’, ‘dc’, and ‘dv’ were evaluated using unit cell software. The absorption peaks at 427 to 538 cm^?1 confirmed the spinel structure, which was evaluated using FTIR. FESEM analyses showed that the agglomerations increased with the doping of Ca in Ni–Mg–Mn ferrites. Remanence, Y–K angles, saturation, coercive force, magnetic squareness, magnetic moment, and anisotropy constant were determined for Ca-doped Ni–Mg–Mn spinel ferrite samples. It is noticed that saturation increases from 29.157 to 51.322 emu/g, whereas remanence increased from 5.34 to 9.40 emu/g, respectively. The permeability, anisotropy constant, and magnetic moments were also found to increase with Ca doping. However, the Y–K angles increased with Ca concentration in Ni–Mg–Mn nano ferrites. In addition, the switching field distribution (SFD) and high-frequency response of all the Ca-doped Ni–Mg–Mn samples were also evaluated. Ca-doped Ni–Mg–Mn samples are suggested to be suitable for switching, filters, inductors, and microwave absorption applications because of the superparamagnetic nature of the prepared spinel ferrites.     

Cobalt ferrite nanoparticles prepared by microwave hydrothermal synthesis and adsorption efficiency for organic dyes: Isotherms,thermodynamics and kinetic studies

Magnetic nanoferrites (MFe₂O₄, M = Co, Ni) were successfully synthesised through microwave-hydrothermal route, characterised and used for adsorption of Eriochrome Black T (EBT) and Bromophenol Blue (BRB) dyes from their aqueous solution. The powder XRD patterns confirmed the formation of cubic spinel structure for both the ferrites. Under identical conditions, the adsorption efficiency of CoFe₂O₄ was found relatively higher than the corresponding NiFe₂O_4. Further characterisations revealed that CoFe₂O₄ sample was nearly spherical in size (8–9 nm) with narrow size distribution. The sample showed superparamagnetic behaviour with saturation magnetization (M_s) value (66.4 emu/g). BET surface area calculated for the synthesized cobalt ferrite as 70.9 m²/g. Batch adsorption experiments as a function of initial dye concentration, pH, contact time and adsorbent dose showed the adsorption of dyes depends on pH. Equilibrium adsorption data were well explained by both Langmuir and Freundlich isotherm models. The maximum monolayer adsorption capacities (Q_o) were found to be 82.6 and 25.6 mg/g for EBT and BRB dyes, respectively. Kinetics of the adsorption was best described by pseudo-second-order model. Various thermodynamic parameters such as ΔG, ΔH and ΔS derived from adsorption data over the temperature range 20–50 °C, accounted for a favourable, spontaneous, endothermic physisorption process. The materials showed potential for repeated use without significant decrease in adsorption capacity after proper regeneration.     

Sol gel derived MnTi doped Co2 W-type hexagonal ferrites: Structural,physical, spectral and magnetic evaluations

W-type BaSr Co₂ hexaferrites doped with Mn and Ti of the following composition Ba_0.5Sr_0.5Co₂Mn_xTi_xFe_16-2xO₂₇ (x = 0.00, 0.50, 1.00, 1.50, 2.00, 2.50) were synthesized by sol-gel auto ignition method. The structure, phase, spectral bands, microstructure, and magnetic behaviors of the MnTi doped BaSr Co₂ W-type ferrites were determined using XRD, FTIR, FESEM, and VSM respectively. Structural and physical parameters such as lattice parameters ‘a’ and ‘c’, crystallite size, cell volume, micro strain, porosity, bulk and X-ray density of the MnTi doped BaSr Co₂ W-type hexaferrites were evaluated. The detailed and refined structural properties were determined using the Rietveld refinement of the MnTi doped BaSr Co₂ W-type hexagonal ferrites. MAUD software was used for the refinement of the MnTi doped BaSr Co₂ W-type hexagonal ferrites patterns. Rb, Rwp and Rexp values were found in the range of 10–19 for MnTi doped BaSr Co₂ W-type hexagonal ferrites. The force constants at respective sites were also investigated through FTIR studies. FESEM images showed the hexagonal shape of the MnTi doped hexaferrites. Magnetic properties were estimated from the hysteresis loops recorded by VSM. The magnetic properties were decreased with the MnTi doping. However, anisotropic field was also found to be decreased with MnTi doping. This might be due to the ionic radii and nonmagnetic substitution of Ti in BaSr Co₂ W-type hexagonal ferrites. The low coercivity values of these ferrites suggest the use of MnTi doped BaSr Co₂ W-type ferrites for microwave absorption, memory devices and magnetic radar absorbing materials (MRAMs) in high frequency regime.     

Morphological and magnetic properties of BaFe12O19 nanoferrite: A promising microwave absorbing material

In this work, ultrapure hexagonal BaFe₁₂O₁₉ nanoferrite was synthesized by a facile co-precipitation method. Formation of single phase was analyzed by using wide angle X-ray diffraction. Crystallite size was found to increase from 50 nm to 78 nm when annealing temperature increased from 800 °C to 1000 °C, respectively. Ferrimagnetic behavior with moderate value of saturation magnetization and coercivity were studied at room temperature with the help of vibrating sample magnetometer (VSM). The electromagnetic radiation (EMR) absorption properties were studied in the frequency range of 2–18 GHz by using Vector Network analyzer (VNA). The maximum EMR absorption of −26.52 dB was observed at a frequency of 5.79 GHz. The FTIR spectra confirm tetrahedral and octahedral sites in BaFe₁₂O₁₉ structure. The surface morphology was analyzed by scanning electron microscopy (SEM), which reveals that the particles are agglomerated into irregular shapes. Particle size was measured with transmission electron microscopy (TEM), which was in correlation with the already calculated size from x-ray diffraction (XRD) spectra.     

Structural,spectral, dielectric and magnetic properties of Ni0.5MgxZn0.5-xFe2O4 nanosized ferrites for microwave absorption and high frequency applications

Ni_0.5Mg_xZn_0.5−xFe₂O₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) (NiMgZn) nano-sized ferrites were synthesized via sol-gel route. The average cation radius, bond lengths (A and B sites), shared (d_AE, d_BE) and unshared edges (d_BEU) of the NiMgZn nanoferrites were determined from the XRD data. FTIR studies confirmed the spinel structure of NiMgZn nanoferrites. The force constant at tetrahedral and octahedral sites were calculated. The surface morphology was investigated from the micrographs. The dielectric parameters such as dielectric constant, dielectric loss factor, loss tangent and Q values with different concentration of Mg in NiZn nanoferrite were evaluated. It was found that the NiMgZn sample at x=0.5 showed high Q values with low dielectric losses at higher frequencies. The squareness ratio and coercivity values confirmed the super paramagnetic behaviour of the NiMgZn nano-sized ferrites. However, the saturation and remanence increased with the increasing Mg contents whereas coercivity values follow the Stoner-Wolforth model for NiMgZn at x=0, 0.2, 0.3 and 0.4. The NiMgZn nano-sized ferrites samples at x=0.1 and 0.5 show the variations in coercivity values which may be due to the strong LS coupling and super-exchange interactions of the metal cations at tetrahedral and octahedral sites. The dielectric and magnetic studies of NiMgZn nano-sized ferritesexplored their application in various technological and industrial fields such as magnetic storage, microwave absorption and high frequency applications.     

Magnetically retrievable nanoscale nickel ferrites: An active photocatalyst for toxic dye removal applications

Nickel ferrite (NiFe₂O₄) nanoparticles were synthesized through the sol-gel auto-combustion method using urea and glycine as mixed fuel. The prepared nanoparticles were investigated for their structural, optical, and magnetic characterizations. Rietveld refined X-ray diffraction (XRD) patterns revealed the development of single-phase cubic spinel. The crystallite size was calculated by using Modified Scherrer's method and the W-H plot was found in the order of 26.6 nm and 25.4 respectively which are nearly the same. The infrared spectrum showed the typical characteristic absorption bands in the range of 400 cm^-1 to 600 cm^-1 belonging to cubic spinel structure. Scanning electron microscopy images showed the spherical nature of the nanoparticles along with agglomeration to some extent. As per the optical study, the prepared nanoparticles have an optical bandgap of 2.59 eV. The magnetic properties were studied through the M − H hysteresis curve showing superparamagnetic nature, the value of saturation magnetization (M_s), coercivity (H_c) was observed 46.20 emu/gm, and 383.2 Oe respectively. The photocatalytic activity of nickel ferrite was studied based on the degradation of methylene blue (MB) dye as a model compound, where the result showed that prepared nanoparticles possessed a good photocatalytic activity against dye degradation. Up to four times catalyst exhibits nearly the same reutilization.