Synthesis of nanocrystalline Ni-Zn ferrite powders by refluxing method

A method named refluxing method has been shown for preparing nanocrystalline Ni-Zn ferrite powders with a narrow particle size distribution. The variation of the samples refluxed for different times has been investigated by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and a recipe for the preparation of nanosized ferrite has been developed. Single-phase Ni-Zn ferrite has been found to form at a temperature of about 107 °C and with a calcination time of 6 h. The average diameter of the powders as-prepared is about 10 nm.     

A review of the structure,magnetic and electrical properties of bismuth ferrite (Bi2Fe4O9)

Nowadays, investigations on the materials with multiferroic properties are in progress. These materials compromise simultaneous electric and magnetic properties. Ferrite Bismuth (FB) is one of the ceramic materials that enjoy this property and possesses three different crystalline structures (perovskite BiFeO₃, selenite Bi₂₅FeO₄₀ and mullite Bi₂Fe₄O₉). In this review, first, the crystalline structure and the electric and magnetic properties of Bi₂Fe₄O₉ are studied, and then, the effects of adding dopants to the ferrite are discussed. Mullite-type bismuth ferrite (Bi₂Fe₄O₉) as a spin frustrated multiferroic has potential for magnetoelectric coupling, and it might be an appropriate alternative for some of the multiferroics that suffer from a weak magnetoelectric coupling.     

Effect of fuel type on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Porous magnetite (Fe₃O₄) powders were synthesized by solution combustion method using the glycine and urea at different fuel to oxidant ratios (ϕ). The combustion behavior depended on the fuel type as characterized by thermal analysis. The structure and phase evolution investigated by X-ray diffraction method showed nearly single phase Fe₃O₄ powders which were achieved only by using the glycine fuel at ϕ=1. The specific surface area and porous structures of the as-combusted Fe₃O₄ powders were characterized by N₂ adsorption-desorption isotherms and scanning electron microscopy, respectively. The surface area using the glycine fuel (62.6 m²/g) was higher than that of urea fuel (42.5 m²/g), due to different combustion reactions. Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry which exhibited the highest saturation magnetization of 74 emu/g using the glycine fuel at ϕ=1 on account of its high purity and large crystallite size.     

Effect of Mg doping on magnetic,and dielectric properties of NiCr2O4 nanoparticles

The structural, magnetic, and dielectric properties of spinel Magnesium (Mg) doped Nickel chromite (NiCr₂O₄) nanoparticles (NPs) have been studied in detail. The X-ray powder diffraction exhibited normal spinel phase formation of Mg_xNi_1-xCr₂O₄ (x = 0, 0.2, 0.4, 0.6, and 1) NPs with a maximum average crystallite size of about 44 nm for x = 0.2 composition. The FTIR spectra of these NPs revealed the characteristic Ni–O and Mg–O and Cr–O bands around 639 cm^?1 and 497 cm^?1, respectively which confirmed the spinel structure. Temperature-dependent zero field cooled and field cooled graphs of NiCr₂O₄ NPs showed phase changes from ferrimagnetic to paramagnetic state at 86 K, while MgCr₂O₄ NPs showed antiferromagnetic (AFM) transition at Neel temperature (T_N) at 15 K due to corner-sharing of Cr³⁺ ions at a tetrahedral lattice site resulting in a highly magnetic frustrated structure. The field dependent magnetization (M ? H) loops of Mg_xNi_1-xCr₂O₄ NPs confirmed the competing AFM interactions and ferrimagnetic interactions resulting in a sharp decreased saturation magnetization with Mg doping. Dielectric constant, dielectric loss, and ac conductivity of these NPs showed size-dependent variation and depicted maximum value at x = 0.2 Mg concentration. In summary, the magnetic and dielectric properties of Mg doped NiCr₂O₄ NPs were modified by variations in the average crystallite size and magnetic exchange interactions, which may be suitable for different technological applications.     

Effects of pH value on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Magnetite (Fe₃O₄) powders were prepared by solution combustion synthesis method using conventional and microwave ignition at various pH values of starting solution, adjusted by NH₄OH. The chelated species in dried gels were predicted by theoretical calculations and Fourier transform infrared spectroscopy. The combustion reaction rate strongly depended on pH values as investigated by thermal analysis. Phase evolution and structure characterized by X-ray diffraction method showed single phase and well-crystalline Fe₃O₄ powders which were achieved using conventional ignition at pH ≥ 7. However, the microwave ignition led to the formation of impure FeO phase together with Fe₃O₄. The microwave combusted powders exhibited the disintegrated structure in comparison with the bulky microstructure for conventionally combusted powders, as observed by scanning electron microscopy. Magnetic properties of the as-combusted powders studied by vibration sample magnetometry showed the highest saturation magnetization of 81.3 emu/g for conventional ignition at pH of 7, due to the high purity and large crystallite size.     

Enhancement of magnetic properties of Ni0.5Zn0.5Fe2O4 nanoparticles prepared by the co-precipitation method

Nano crystalline Ni–Zn ferrites of composition Ni_0.5Zn_0.5Fe₂O₄have been prepared by a chemical co-precipitation method. The powdered samples were sintered at a temperature of 800 °C and 900 °C for three hours. X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared (FTIR) Spectroscopy were used to study their structural and morphological changes. The enhanced magnetic properties were investigated by using a Vibrating Sample Magnetometer (VSM). The saturation magnetization was found to increase from 73.88 to 89.50 emu/g as a function of sintering temperature making this material useful for high frequency applications. Electromagnetic studies showed sustained values of permittivity up to 1 GHz. These results have been explained on the basis of various models and theories.     

Microstructure and microwave-frequency electromagnetic properties of Ni0.4Zn0.6Fe2O4/Ba0.6Sr0.4TiO3 composites

(x)Ni_0.4Zn_0.6Fe₂O₄+(1−x)Ba_0.6Sr_0.4TiO₃ composite ceramics with x=0.6, 0.7, 0.8, 0.9 and 1 were synthesized by solid state reaction method. The high dense composites have only two phases, i.e., Ni_0.4Zn_0.6Fe₂O₄ and Ba_0.6Sr_0.4TiO₃. The permittivity ε′ of the composites decreases slightly with the frequency increasing from 3 MHz to 1 GHz. The permittivity ε′′ of the composites also shows a little increase with frequency in the 3 MHz–1 GHz range. The permeability displays a relaxation resonance within the 3 MHz–1 GHz frequency range. The permeability μ′ increases while the cut-off frequency decreases with the Ni_0.4Zn_0.6Fe₂O₄ concentration, obeying the Snoek's law μ_if_r=constant. The permittivity ε′ of the composites decreases with Ni_0.4Zn_0.6Fe₂O₄ concentration. The composites have a relatively higher ε′ than the pure Ni_0.4Zn_0.6Fe₂O₄ at 1–10 GHz. In the frequency range of 1–10 GHz, the magnetic permeability μ′ reaches its maximum and μ′′ shows a minimum for the composite with x=0.6 in all ceramics. The permeability μ′ of the composites decreases with dc magnetic field at 1–10 GHz. The permeability shows a domain wall resonance, and the resonance frequency shifts to high frequency with the dc magnetic field. The permittivity was also influenced by the dc magnetic field due to a magnetodielectric effect.     

Temperature induced evolution of structure/microstructure parameters and their correlations with electric/magnetic properties of nanocrystalline Nickel ferrite

Nickel ferrite nanoparticles were annealed in order to find dependence of electric/magnetic properties on crystallite size. The following correlations of crystallite size with physical parameters were found: (a) lattice parameter decreases with the increase in size and it reaches value for bulk counterpart approximately for crystallites bigger than 7 nm, (b) ac electrical resistivity at room temperature increases with the increase in crystallite size, (c) for crystallites of ~7 nm or smaller electrical resistivity have maximum value at 50 °C, (d) the real part of permittivity at selected frequency generally decreases with the increase in crystallite size and (e) magnetization increases with the increase in crystallite size. Deviation of stoichiometry, cation polyvalence, and cation redistribution with annealing are the main factors that influence physical properties of Nickel ferrite nanoparticles.     

Synthesis and characterization of NiO and Ni nanoparticles using nanocrystalline cellulose (NCC) as a template

In this study, nanosized nickel oxide (NiO) and nickel (Ni) powders were synthesised via glycine-nitrate (GN) combustion process, assisted by nanocrystalline cellulose (NCC) as a template. Despite the unique morphology of NCC, it has yet to be applied as a sacrificial bio-template for GN combustion process. In addition, NiO and Ni nanoparticles were obtained at relatively low temperatures in this study, whereby the calcination temperatures were varied from 400 °C to 600 °C, with calcination durations of 2, 4, and 6 h. The morphological analysis of the resulting products were conducted using FESEM, which showed uniformly dispersed NiO and Ni particles with average crystallite size of 25 nm and 27 nm, respectively. These results were confirmed using X-ray diffraction (XRD) technique. The Raman and Fourier transform infrared (FTIR) spectra revealed that the molecular fingerprints of the samples were in agreement with each other. Further analyses revealed that samples calcined at 600 °C for 4 h showed the lowest particle size for pure NiO, whereas the lowest particle size for pure Ni was obtained at 400 °C for 4 h. The TGA results were also consistent with the XRD analysis, whereby pure Ni was initially formed and upon heating, had gradually converted into NiO.     

Structural and magnetic properties of strontium substituted NiZn ferrite nanopowders

Sr-substituted NiZn ferrite nanopowders, Ni_0.5-xZn_0.5Sr_xFe_2.0O₄ (0≤x≤0.20), were synthesized by the sol-gel auto-combustion method. The effects of Sr substitution on the structural and magnetic properties have been investigated. Differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements were used to characterize chemical, structural and magnetic properties. The DTA-TG results indicate that there are three steps of combustion process. XRD results indicate that the lattice parameter increases, and the average crystallite size decreases with increasing Sr substitution. The Sr₂FeO₄ and SrFe₁₂O₁₉ impurity phases formed with excess Sr substitution. The saturation magnetization monotonically decreases with the increase of Sr substitution. Meanwhile, the coercivity initially decreases with the increase of Sr substitution when x≤0.15, and increases when x>0.15.     

Electrical and magnetic properties of ZrO2-doped lithium-titanium-zinc ferrite ceramics

This report documents the effect of 0–3 wt% ZrO₂ additive on the electrical and magnetic properties of LiTiZn ferrite. Ferrite powder of Li_0.65Fe_1.6Ti_0.5Zn_0.2Mn_0.05O₄ composition was synthesised at 900 °C for 4 h in air. Ferrite ceramics doped with ZrO₂ were sintered at 1010 °C for 2 h in air. A spreading resistance analysis showed that LiTiZn ferrites exhibited nonuniform distribution of depth DC resistivity, which varied in the range of (0.25–2.3) × 10⁹ Ω⋅cm depending on the amount of additive. Zirconia also affected the magnetic properties of ferrite so that the magnetisation increased and the initial permeability decreased as the ZrO₂ content increased. In addition, the Curie temperature varied. The permeability spectra measured in the frequency range from 10 MHz to 18 GHz changed depending on the zirconia content.     

Synthesis of Co-Zr doped nanocrystalline strontium hexaferrites by sol-gel auto-combustion route using sucrose as fuel and study of their structural,magnetic and electrical properties

Sol-gel auto-combustion route using sucrose as fuel has been employed to synthesize nanocrystalline particles of SrZr_xCo_xFe_(12−2x)O₁₉ (0.0≤ x ≤1.0). The characterization of these materials has been done by TGA-DTA, FT-IR, XRD and EDS. SEM and TEM techniques have been used to study the structure and morphology. Magnetic properties have been investigated by VSM and Mössbauer spectroscopy (MS). The influence of calcination temperature on morphology and magnetic properties of samples is studied in a wide temperature range of 500–1100 °C. XRD analysis indicates the formation of pure single phase hexagonal ferrites at 900 °C. The crystallite size calculated using Scherrer equation lies in a narrow range of 21–33 nm. The crystallite size is small enough to obtain a suitable signal to noise ratio in high density recording medium. Substitution of Zr and Co for Fe has been found to have a profound effect on the structural, magnetic and electrical properties. Upon substitution saturation magnetization (M_S) first increases from 62.67 emu/g to 64.84 emu/g (up to x=0.4) followed by a decrease to 49.71 emu/g at x=1.0. There is a slow fall in coercivity (H_C) from 5785.74 (x=0.0) to 1796.51 Oe (x=1.0). Dielectric constant, dielectric loss tangent and AC conductivity in the frequency range 20 Hz to 120 MHz have been studied for all the compositions (x=0–1.0). The composition and frequency dependence of these dielectric parameters has been qualitatively explained.     

Cation distributions and magnetism of Al-substituted CoFe2O4 - NiFe2O4 solid solutions synthesized by sol-gel auto-combustion method

Aluminium substituted cobalt-nickel ferrite nanoparticles were synthesized by citrate gel auto-combustion method followed by annealing at 1000?°C for 1?h in air. Scanning electron micrographs of all the samples show crystalline particles of irregular morphology with a small variation in particle sizes (~ 110–160?nm). From the analysis of the X-ray diffraction results we observed that the unit cell parameter decreases linearly with increase in aluminium concentration due to the smaller ionic radius of the Al³⁺ ions substituting the other cations such as Co²⁺, Ni²⁺ and Fe³⁺ ions in the compounds. The room temperature Mössbauer spectra of the samples show Zeeman split sextet patterns corresponding to the tetrahedral (Th) and octahedral (Oh) interstitial iron (Fe³⁺) cations. The observed magnetic hyperfine field (B_hf) decreases with increase in Al-concentration due to the distribution of diamagnetic Al³⁺ in the environment of ⁵⁷Fe probe atoms. The saturation magnetization measured by Vibrating Sample Magnetometer (VSM) shows a similar trend like that of B_hf. The distributions of the cations obtained from the Rietveld refinement and Mössbauer spectroscopy results indicate an increase in Fe³⁺(Th)/Fe³⁺(Oh) occupancy-ratio on increasing Al³⁺ concentration, and Ni²⁺ cations prefer the octahedral site, whereas Co²⁺ and Al³⁺ ions redistribute themselves in tetrahedral and octahedral sites, in the ratio 2:3.     

Synthesis and Characteristics of Superparamagnetic Co0.6Zn0.4Fe2O4 Nanoparticles by a Modified Hydrothermal Method

Nanoparticles of Co_0.6Zn_0.4Fe₂O₄, with narrow size distribution, regular morphology, and high saturation magnetization, have been synthesized. The synthesis, involved a very rapid mixing of reducible metal cations with sodium borohydride, is carried out in a colloid mill and followed by a separate hydrothermal process. The microstructure and magnetic properties of the synthesized nanoparticles are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The effects of different synthesis conditions (synthesis temperature and reaction time) on the characteristics of the ferrite nanoparticles are discussed. The changes in cation contribution are revealed by the Raman study. The magnetic measurements explore that all the as‐synthesized samples are superparamagnetic in nature. The corresponding superparamagnetic behavior is explained by paramagnetic Langevin theory. Note that, the superparamagnetic Co_0.6Zn_0.4Fe₂O₄ ferrite nanoparticle, with excellent performance, can be synthesized at 160°C for a short reaction time (4 h).     

Structural,dielectric, and magnetic properties of reduced graphene oxide-wrapped MnFe2O4 composites synthesized by in-situ sol-gel autocombustion method

Herein, the reduced graphene oxide (rGO) wrapped MnFe₂O₄ (MFO@rGO) composites with different rGO content of 10, 20, 30, and 40 wt% have been synthesized by a one-step in-situ sol-gel autocombustion method. The synthesized composites have been tested for their structural, electrical, dielectric, and magnetic characteristics. The composites are characterized by using standard techniques (XRD, HR-TEM, FTIR, and Raman spectroscopy). The composite having 20 wt% of rGO exhibits the highest value of dielectric constant (ε′～1.32 × 10⁴ at 100 Hz, ε′～143 at 1 MHz) and dc conductivity (σ_dc = 4.31 × 10^?6 Ω^?1-cm^?1) among the investigated composites. The dipole polarization contribution to the dielectric relaxation behavior of MFO@rGO composites is observed, which arises from the increased vacancy defect dipoles in rGO sheets. The impedance studies show the existence of two different time relaxation phenomena in MFO@rGO composites. The magnetic measurements reveal the superparamagnetic behavior of composites. The saturation magnetization of composites decreases first with the increase in rGO content up to 20 wt% and then increases with a further increase in rGO content. The findings of this research make these composites a potential candidate for various applications such as EMI shielding and energy storage devices.     

Microwave absorption properties of Ni0.6Zn0.4Fe2O4 composites with nonmagnetic nanoferrite percentages

Microwave absorption materials need to be thin and lightweight and possess strong wave absorption ability and a wide absorption frequency band. To satisfy these conditions, we changed the microstructure of the composite by mixing ferrite material with different particle sizes. Specifically, we mixed nanosized nonmagnetic ZnFe₂O₄ powder into Ni_0.6Zn_0.4Fe₂O₄ powder, investigated the microwave absorption properties depending on the packing fraction. The crystal structure of the synthesized ferrite powders was analyzed through XRD, and the particle size was analyzed using a PSA and SEM. The density of the powders, which is required to measure the packing fraction, was determined via the gas disposition method, and the magnetic properties of the composites were analyzed using a VSM. The reflection loss represents the electromagnetic wave absorption characteristics, and it was calculated by substituting the measured permittivity and permeability values, into the equation based on the transmission line theory. The Ni_0.6Zn_0.4Fe₂O₄/ZnFe₂O₄ composite showed 99.9% absorption with a high packing fraction, and the absorption peak shifted to high frequencies. These characteristics suggest that the absorption ability and frequency range of the electromagnetic-wave-shielding composite can be easily controlled. Because of the high-absorption characteristic, absorption frequency control, and cost effectiveness, this composite can be applied to products such as thin electromagnetic-wave-shielding sheets.     

Impact of Zn doping on the dielectric and magnetic properties of CoFe2O4 nanoparticles

Owing to its unique magnetic, dielectric, electrical and catalytic properties, ferrite nanostructure materials gain vital importance in high frequency, memory, imaging, sensor, energy and biomedical applications. Doping is one of the strategies to manipulate the spinel ferrite structure, which could alter the physico-chemical properties. In the present work, Co_1-xZn_xFe₂O₄ ($x$ = 0, 0.1, 0.2, 0.3, and 0.4 wt%) nanoparticles were prepared by sol-gel auto-combustion method and its structural, morphological, vibrational, optical, electrical and magnetic properties were studied. The structural analysis affirms the single-phase cubic spinel structure of CoFe₂O₄. The crystallite size, lattice constant, unit cell, X-ray density, dislocation density and hopping length were significantly varied with Zn doping. The Fe–O stretching vibration was estimated by FTIR and Raman spectra. TEM micrographs show the agglomerated particles and it size varies between 10 and 56 nm. The Hall effect measurement shows the switching of charge carriers from n to p type. The dielectric constant (ε′) varies from 0.2 × 10³ to 1.2 × 10³ for different Zn doping. The VSM analysis shows relatively high saturation magnetization of 57 and 69 emu/g for ZC 0.1 and ZC 0.2 samples, respectively than that of undoped sample. All the prepared samples exhibit soft magnetic behaviour. Hence, it can be realized that the lower concentration of Zn ion doping significantly alters the magnetic properties of CoFe₂O₄ through variation in the cationic distribution and exchange interaction between the Co and Fe sites of the inverse spinel structure of CoFe₂O_4.