Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

Synthesis and study of nanocrystalline Ni-Cu-Zn ferrites prepared by oxalate based precursor method

Nanocrystalline ferrites of compositions Ni_0.5+1.5xCu_0.3Zn_0.2Fe_2−xO₄ (0 ≤ x ≤ 0.5) have been synthesized by using oxalate based precursor method at very low temperature. The Ni-Cu-Zn ferrite powder particles were obtained at 450 °C and they exhibit a crystallite size of 16-24 nm. The lattice constants were found nearly equal in all these samples due to minute difference in the ionic radius between Ni²⁺ and Fe³⁺ ions. The thermal analysis has showed the ferrite phase formation at very low temperature 377 °C. The two main spectroscopic bands corresponding to lattice vibrations were observed in the wavelength range from 300 to 1000 cm⁻¹. The IR bands at 570 cm⁻¹ (v₁) and 390 cm⁻¹ (v₂) were assigned to tetrahedral (A) and octahedral [B] groups. The spectroscopic bands shift with the increase of doping concentration. The magnetization was found to decrease with increasing doping concentration. The dielectric constant (?′) and dielectric loss tangent (tan δ) decreased with increase of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrite samples appeared to be lower than that of the ferrites prepared by other synthesis techniques.     

Role of Cr ions on the microstructure development, and magnetic phase evolution of Ni0.7Zn0.3Fe2O4 ferrite nanoparticles

A series of ferrite samples with the chemical formula Ni_0.7Zn_0.3Cr_xFe_2−xO₄ (x = 0.0-0.5) were prepared by a sol-gel auto-combustion method and annealed at 600 °C for 4 h. The resultant powders were investigated by various techniques, including X-ray diffractometry (XRD), vibrating sample magnetometry (VSM), and permeability studies. The prepared samples have a cubic spinel structure with no impurity phase. As the Cr³⁺ content x increases, bulk density and crystallite size decrease, whereas porosity increases. The saturation magnetization decreases linearly from 58.31 to 42.90 emu/g with increasing Cr³⁺ content. However, coercivity increases with increasing Cr³⁺ substitution. The magnetic moments calculated from Neel's molecular-field model are in agreement in the experiment results. The initial permeability (μ_i) decreases with increasing Cr³⁺ substitution. The decrease in initial permeability (μ_i) is attributed to decrease in magnetization on addition of Cr³⁺. The real part of the permeability decreases gradually with increasing frequency in accordance with Snoek's law. The Curie temperature decreases linearly with increasing Cr³⁺ content.     

Effect of Gd doping on magnetic, electric and dielectric properties of MgGdxFe2−xO4 ferrites processed by solid state reaction technique

MgGd_xFe_2−xO₄ (x = 0.0, 0.05, 0.1 and 0.15) ferrites, with improved dc resistivity, initial permeability, saturation magnetization, and extremely low relative loss factor, have been synthesized by solid state reaction technique. The microstructures, electric, dielectric and magnetic properties have been investigated by means of X-ray diffraction, Keithley 2611 system, impedance analyzer and VSM respectively. The addition of Gadolinium in Mg ferrite has been shown to play a crucial role in enhancing the electric, dielectric and magnetic properties. The dc resistivity is increased by two orders of magnitude as compared to Mg ferrite. Saturation magnetization has been increased by two times and remnant magnetization has been increased by more than three times due to the doping of Gd³⁺ ions in Mg ferrite. The relative loss factor was found to have very low values and is of the order of 10⁻⁴-10⁻⁵ in the frequency range 0.1-30 MHz. The variations of electric, dielectric and magnetic properties of the samples have been studied as a function of frequency and Gd³⁺ ions concentration measured at room temperature. High resistivity and improved magnetic properties can be correlated with better compositional stoichiometry and the replacement of Fe³⁺ ions by Gd³⁺ ions. The mechanisms responsible to these results have been discussed in this paper.     

Structural, optical and transport properties of Al doped BiFeO3 nanopowder synthesized by solution combustion method

Aluminum doped Bismuth ferrite (BFO) nanopowders (grain size 13-20 nm) having composition Bi_1−xAl_2xFe_1−xO₃ (x = 0.00, 0.025, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were successfully synthesized by solution combustion method using citric acid as fuel at a temperature as low as 200 °C. As-prepared samples were examined by powder XRD for phase identification and crystallite size determination. The d.c. resistivity as a function of temperature was measured by standard two probe setup which exhibits clear metal to insulator transition for all samples. FTIR analysis was carried out to identify the chemical bonds present in the system. The optical band gap was calculated from the UV-vis absorbance spectra using classical Tauc relation which was found to vary from 2.78 eV to 2.93 eV for different Al³⁺ concentrations. The activation energies calculated from the slopes of ln(ρ) versus 10³/T plots are in the range 0.54-0.73 eV.     

Structural, magnetic and electrical properties of Al substituted Ni-Zn ferrite nanoparticles

Nanocrystalline ferrite materials having the general formula Ni_0.7Zn_0.3Fe_2−xAl_xO₄ (0.0 ≤ x ≤ 0.5) have been synthesized by citrate-gel auto combustion method and characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FE-SEM), dc magnetization, dielectric and impedance spectroscopy measurements. XRD studies confirm that all the samples show single phase cubic spinel structure. The crystallite size of Ni_0.7Zn_0.3Fe_2−xAl_xO₄ (0.0 ≤ x ≤ 0.5) nanoparticles calculated using the Debye-Scherrer formula was found in the range of 13-17 nm. The value of lattice parameter ‘a’ is found to decrease with increasing Al³⁺ content. EDX patterns confirm the compositional formation of the synthesized samples. FE-SEM micrographs show that all the samples have nano-crystalline behavior and particles show spherical shape. The variation of dielectric properties ?′,?″, and tan δ with frequency shows the dispersion behavior which is explained in the light of Maxwell-Wagner type of interfacial polarization in accordance with the Koop's phenomenological theory. The dc magnetization studies infer that magnetic moment of Ni_0.7Zn_0.3Fe_2−xAl_xO₄ (0.0 ≤ x ≤ 0.5) nanoparticles was found to decrease with Al doping. Impedance spectroscopy techniques have been used to investigate the effect of grain and grain boundary on the electrical properties of the synthesized compounds.     

Effect of ZrO2 addition on the microstructure and electromagnetic properties of YIG

In this work, we reported the microstructure and electromagnetic properties of a series of zirconium substituted yttrium iron garnet ferrites (YCaZrIG) with iron deficiency composition of Y_3−xCa_xZr_xFe_4.93−xO₁₂ (x = 0.1, 0.2, 0.3, and 0.4, with electrostatic balance by Ca²⁺ substituted for Y³⁺ ions) prepared by a solid-reaction method. The addition of ZrO₂ shows no obvious influence on the phase, density and dielectric constant of YIG ferrites. When Zr addition x ≤ 0.3, the substitution of Zr⁴⁺ for Fe³⁺ decreases the amount of Fe ions, increases the lattice parameter and enhances the grain growth of garnet phase. The solubility of zirconium in YCaZrIG ferrite was found to be approximately 0.3, above which excess ZrO₂ would lead to the precipitation of a second phase inside the YCaZrIG ferrite. This would inhibit the grain growth of garnet phase and cause an increase in the dielectric loss and coercivity. The observed reduce for saturation magnetization when x = 0.4 is possibly due to antiparallel alignment of magnetic moment of Fe³⁺ in the d site caused by the decrease of a-d exchange interaction. Additionally, we got the optimum electromagnetic properties in the samples with x = 0.3: ?_r = 14.1, tan δ_e = 2.5 × 10⁻⁴, H_c = 47 A/m, 4πM_s = 1936 × 10⁻⁴T, ΔH = 7.1 KA/m.     

Mn-Zn soft magnetic ferrite nanoparticles synthesized from spent alkaline Zn-Mn batteries

Using spent alkaline Zn-Mn batteries as raw material, Mn-Zn soft magnetic ferrite nanoparticles are prepared by multi-step processes including acid leaching, chemical treatment of battery iron shells and citrate-nitrate precursor auto-combustion. Acid leaching and chemical treatment mechanisms are investigated. Dried gels thermal decomposition process, auto-combustion, phase composition, morphological and magnetic properties of as-prepared Mn-Zn ferrite nanoparticles are characterized by thermogravimetric and differential thermal analysis, X-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. Synthesized Mn-Zn ferrite nanoparticles (Mn_0.5Zn_0.5Fe₂O₄) have pure ferrite phase, larger saturation magnetization (M_s = 60.62 emu g⁻¹) and lower coercivity (H_c = 30 Oe) compared with the same composition ferrites prepared by other techniques due to better crystallinity. Mn-Zn ferrite nanoparticles synthesis method presents a viable alternative for alkaline Zn-Mn batteries recycling.     

Synthesis, structural and magnetic characterization of nanocrystalline nickel ferrite—NiFe2O4 obtained by reactive milling

Nanocrystalline nickel ferrite (NiFe₂O₄) has been synthesized from a stoichiometric mixture of oxides NiO and α-Fe₂O₃ in a high energy planetary mill. An annealing at 350 °C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure.     

Negative magnetization, magnetic anisotropy and magnetic ordering studies on Al-substituted copper ferrite

Detailed magnetic properties of Al³⁺-modified CuFe₂O₄ spinel ferrite system: CuAl_xFe_2−xO₄; x = 0.0, 0.2, 0.4 and 0.6, have been studied by means of X-ray powder diffraction, field cooled (FC) and zero field cooled magnetization (ZFC) (H = 10 mTesla, T = 4-325 K), magnetic hysteresis (H_max = 2 Tesla, T = 10 and 300 K) and low field (40 A/m) ac susceptibility (T = 300-750 K) measurements. The system exhibits canted spin structure. It has been shown that the observed features of the FC-ZFC magnetization and ac susceptibility curves arise due to the low magneto crystalline anisotropy, not due to the cluster spin-glass-like magnetic ordering. The interesting features like low temperature cusp in the ZFC magnetization for all the compositions and negative magnetization for x = 0.6 composition have been observed. An attempt has been made to explain the negative magnetization within the framework of available models.     

Hydrothermal synthesis and photoluminescence of Ce and Tb doped La2Sn2O7 nanocrystals

Phase-pure Ce-/Tb-doped and co-doped lanthanum stannates (La₂Sn₂O₇) nanocrystals were synthesized by a co-precipitation process combined with hydrothermal techniques without any further heat treatment. The crystal structure, particle size, morphologies, and photoluminescence properties of the as-synthesized products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The as-prepared samples were single-phase cubic pyrochlore-type nanocrystals with a typical size of 10-20 nm. PL spectra showed a dominating green-emitting line around 544 nm attributing to ⁵D₄-⁷F₅ magnetic dipole transition for Tb³⁺ doped and Ce³⁺/Tb³⁺ co-doped La₂Sn₂O₇ nanocrystals. Meanwhile, the concentration quenching phenomenon was observed in both La_2−xTb_xSn₂O₇ and La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals. Furthermore, an interesting enhancement of the energy transfer induced green emission was observed in the as-synthesized La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals.     

Synthesis and characterization of Er doped CaF2 nanoparticles

Er³⁺ doped CaF₂ nanoparticles were synthesized by a chemical co-precipitation method. Effect of the dopant concentrations on the structure and optical properties of the CaF₂ nanoparticles was investigated. The X-ray powder diffraction and transmission electron microscopy analysis was used to characterize the structure and morphology of the nanoparticles. The nanoparticles with different dopant concentration exhibited a sphere-like morphology with diameters of about 8-36 nm. The incorporation of Er³⁺ ions into CaF₂ resulted in the decrease in grain size and deterioration of crystallinity, but enlarged the lattice constants of CaF₂. Additional annealing treatment at 400 °C to the prepared CaF₂ removed the NO₃⁻ and OH⁻ groups adsorbed on the particles’ surfaces, and improved the optical properties of the nanoparticles. The fluorescence intensity, with a maximum at approximately 0.4 mol%, decreased with the increase in doping concentration because of concentration quenching.     

Studies on the magnetic, magnetostrictive and electrical properties of sol-gel synthesized Zn doped nickel ferrite

Zinc doped nickel ferrite i.e., Ni_1−xZn_xFe₂O₄ (0 ≤ x ≤ 0.6) have been prepared by using sol-gel method. X-ray diffraction of these samples shows the presence of single-phase cubic spinel structure. The room temperature magnetic measurements showed that saturation magnetization (M_s) increases with the substitution of Zn²⁺ ions up to x = 0.4 and thereafter it begins to decrease, whereas magnetostriction (λ) value decreases with the addition of Zn²⁺ in the Ni-Zn ferrite. Dielectric permittivity (?′), dielectric loss tangent (tan δ) and AC conductivity (σ_AC) for all the prepared samples have been studied as a function of frequency and composition in the range from 0.05 Hz to 10 MHz at room temperature. It has been observed that initially ?′, tan δ and σ_AC decreases with the substitution of Zn²⁺ up to x = 0.4 and then increases with the further addition of Zn²⁺ ions. Variation in the slope parameter s with zinc contents indicates the presence of different type of conduction mechanism in different compositions. The dielectric loss curves exhibit relaxation peaks which shift with the addition of Zn contents. The results have been explained on the basis of space charge polarization according to Maxwell-Wagner's two-layer model and the hopping of charges between Fe²⁺ and Fe³⁺ as well as between Ni³⁺ and Ni²⁺ ions at the octahedral sites.     

Structural, dielectric and magnetic properties of Nd-doped Co2Z-type hexaferrites

Z-type hexaferrites doped with Nd³⁺, Ba_3−xNd_xCo₂Fe₂₄O₄₁ (x = 0, 0.05, 0.10, 0.15, and 0.25), were prepared by solid-state reaction. The effect of the Nd³⁺ ions substitution for Ba²⁺ ions on the microstructure and electromagnetic properties of the samples was investigated. The results reveal that an important modification of microstructure, complex permeability, complex permittivity, and static magnetic properties can be obtained by introducing a relatively small amount of Nd³⁺ instead of Ba²⁺. SEM image shows that the grains of the ferrites doped with Nd³⁺ were smaller, more perfect and homogeneous than that of the pure ferrite. The real part (?′) of complex permittivity and imaginary part (?″) increase at first, and then decrease with increasing Nd content. At low frequency, the imaginary part μ″ of complex permeability decreases with Nd content and then increases when frequency is above 7.0 GHz. The magnetization (M_s) and the coercivity (H_c) are 79.38 emu g⁻¹ and 36.94 Oe for Ba_2.75Nd_0.25Co₂Fe₂₄O₄₁. The data of magnetism show that the ferrite doped with Nd³⁺ ions is a better soft magnetic material due to the higher magnetization and lower coercivity.     

Influence of surfactants on co-precipitation synthesis of strontium ferrite

Strontium ferrite (SrFe₁₂O₁₉) particles were prepared by co-precipitation method. The ferrite precursors were produced from aqueous mixtures of ferric chloride and strontium nitrate by co-precipitation, using 3 mol/L sodium hydroxide aqueous solutions as precipitant. Three surfactants sodium dodecyl sulfate (SDS), polyethylene glycol 6000 (PEG-6000), cetyltrimethylammonium bromide (CTAB), were applied and the influence of surfactants on the properties of the strontium ferrite particles was studied. The ferrite precursors were first precalcined in a muffle furnace at 400 °C and then mixed with KCl and NaCl using a planetary milling machine in order to lower the calcination temperature. Subsequently the mixtures were calcined at various temperatures. Structure and magnetic properties of the particles were characterized by X-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. In this paper, effects of Fe³⁺/Sr²⁺ mole ratio were first verified and annealing temperatures were then discussed. The results show the strontium ferrite phase begins to form at 650 °C and complete at 800 °C after calcination, and the particles prepared using CTAB exhibit the best properties with respect to particle size and dispersibility.     

Synthesis and functional properties of the Ni1−xMnxFe2O4 ferrites

Nanocrystalline Ni_1−xMn_xFe₂O₄ (x = 0; 0.17; 0.34; 0.5) ferrite powders were successfully synthesized using the sol-gel combustion method, by using nitrates as cations source and citric acid (C₆H₈O₇) as combustion/chelating agent. The reaction advancement was observed by means of IR absorption spectroscopy, by monitoring two characteristic bands for the spinel compounds at about 600 cm⁻¹ and 400 cm⁻¹, respectively. The as-synthesized powders were characterized by IR spectroscopy, X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The magnetic study shows that the saturation magnetization decreases with increasing the Mn addition, as result of the particle size reduction. The dielectric properties were measured as a function of frequency in the range of 10 Hz to 1 MHz. The real part of permittivity has values of ∼88 at 1 kHz and ∼7 at 1 Hz for x = 0. An increasing dielectric permittivity with increasing the amount of Mn is observed. For all the investigated compositions, both the real and imaginary parts of permittivity decrease with frequency.     

Producing nanocrystalline bulk Mg-3Al-Zn alloy by powder metallurgy assisted hydriding-dehydriding

Nanocrystalline bulk Mg-3Al-Zn alloy with an average grain size of 48 nm has been prepared by powder metallurgy assisted hydriding-dehydriding. Evolutions of nanograined structure powders and bulk alloy have been investigated by TEM, SEM and XRD, respectively. The results showed that by milling in hydrogen for 60 h, as-hydriding powder possessed an average grain size of 5.9 nm. After a subsequent process of desorption-recombination treatment (at 350 °C) and consolidation process (extruded at 200 °C) resulted in bulk samples with an average crystallite size of 48 nm and MgH₂ was fully turned into Mg. The consolidated samples of 60 h milled powder had a final density of 1.77663 ± 0.006 g/cm³, which corresponded to 97.57 ± 0.3% of theoretical density. The highest microhardness of the nanocrystalline bulk alloy reached about 872.5 MPa, which is about three times higher than that of the coarse-grained AZ31.     

High rate of copper electrodeposition from the hexafluorosilicate bath

A high-rate copper electrodeposition performed from a hexafluorosilicate bath is presented in this article. It is shown that the current density for electrodeposition ranges from 1 to 30 A dm^− 2 and the optimal suggested current density is 15 A dm^− 2 or a rate of 200 μm h^- 1. High plating rate is due to a higher mass transport through the hexafluorosilicate media when compared to a conventional sulphate-based bath. The microstructure, texture and mean grain size of the 30 μm-thick films plated from the additive free bath and the bath containing 10^− 3 mol dm^− 3 thiourea and 500 ppm Cl⁻ is studied with respect to the applied current density. Copper plated from the bath without additives has a macrocrystalline structure with preferable 110 texture and mean grain size of 65-85 nm, while thiourea produces a microsmooth surface and 111 texture with grain size of 40-70 nm.     

Influence of chromium substitution on structural and magnetic properties of BaFe12O19 powder prepared by sol-gel auto combustion method

The nanocrystalline Cr³⁺ substituted barium hexaferrite having generic formula BaFe_12−xCr_xO₁₉ (where x = 0.00, 0.25, 0.50, 0.75, and 1.00) samples were synthesized by sol-gel auto-combustion technique. The precursors were prepared by using stoichiometric amounts of Ba²⁺, Fe³⁺ and Cr³⁺ nitrate solutions with citric acid as a chelating agent. The metal nitrate to citric acid ratio was taken as 1:2 while pH of the solution was kept at 8. The thermal decomposition of nitrate-citrate gels of as-prepared powder was investigated by TG/DTA. The as-prepared powder of BaFe_12−xCr_xO₁₉ was sintered at 900 °C for 8 h. The sintered powder was characterized by XRD, EDAX, SEM and VSM technique. The pure barium hexaferrite shows only single phase hexagonal structure, while for the samples at x = 0.25, 0.50, 0.75 and 1.00 shows α-Fe₂O₃ peaks with M-phase of barium hexaferrite. The lattice parameters (a and c) decreases with increase in chromium content x. The particle size obtained from XRD data is in the range of 30-40 nm which confirms the nanocrystalline nature of the samples. The magnetic properties were investigated by means of vibrating sample magnetometer (VSM) technique. The saturation magnetization (M_s), remanence magnetization (M_r), coercivity (H_c) and magneton number (n_B) decreases with increase in chromium content x.     

Study of manganese ferrite powders prepared by a soft mechanochemical route

Manganese ferrite, MnFe₂O₄ have been prepared by a soft mechanochemical route from mixture of (a) Mn(OH)₂ and α-Fe₂O₃ and (b) Mn(OH)₂ and Fe(OH)₃ powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the MnFe₂O₄ spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements. The spinel phase formation was first observed after 12 h of milling and its formation was completed after 25 h in both cases. The synthesized MnFe₂O₄ ferrite has a nanocrystalline structure with a crystallite size of about 40 and 50 nm respectively for cases (a) and (b). There are five Raman active modes. Measurements after 25 h of milling show magnetization values of 70.4 emu/g and 71.1 emu/g respectively for cases (a) and (b). In order to understand better the whole process of phase formation, Mössbauer measurements were done.