Studies on the Properties of Manganese Substituted Nickel Ferrite Nanoparticles

Mn²⁺-substituted Ni ferrite nanoparticles were synthesized by sol-gel auto combustion method. The synthesized samples were annealed at 800 ^°C and characterization studies were carried out by XRD, VSM, electron paramagnetic resonance (EPR), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. The XRD patterns revealed that Mn ²⁺-substituted Ni ferrite crystallizes in cubic spinel phase and addition of α-Fe ₂ O ₃ phase was also observed. The average crystallite sizes were found to be from 42 to 56 nm using a Scherer equation. The coercivity and remanent magnetization decreases when Mn ²⁺ ion concentration is increased. The EPR spectrum shows the phase homogeneity of the samples. The FE-SEM images revealed that particles are both spherical in shape and particle sizes varied from 22 to 41 nm. The FT-IR spectrum confirmed the two main metal ion vibrations of nickel ferrite near 550 to 560 cm ^?1 (A site) and 441 to 460 cm ^?1 (B site).     

Effects of Gd2O3 on structure and magnetic properties of Ni-Mn ferrite

The emulsion method was used to prepare nanocrystalline Ni_0.7Mn_0.3Gd _x Fe_2-x O₄ ferrites. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd₂O₃ on magnetic properties of Ni-Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30–40 nm, all the samples have the similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped-Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions can’t enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd³⁺ ions are larger than that of Fe³⁺ ions. The ferrimagnetism have not disappeared completely, even if the crystallite size is 7.8 nm.     

Study of structural and magnetic properties of (Co–Cu)Fe2O4/PANI composites

The nanocomposites of the polyaniline and Co_1−xCu_xFe₂O₄ (PANI/CoCuFe) were prepared by in-situ oxidative polymerization of aniline. Prepared nanocomposites samples were characterized by using various experimental techniques like X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), Mössbauer spectroscopy and ultraviolet–visible spectrophotometry (UV–VIS). The elemental analysis as obtained from the energy dispersive X-ray spectroscopy (EDAX) measurement is in close agreement with the expected composition from the stoichiometry of the reactant solutions. XRD result confirms that all the samples have the single phase cubic spinel structure. Unit cell parameter ‘a’ is found to decrease with the increase in copper ion substitution. The crystallite size was investigated by using the Debye–Scherer formula and it was found in the range of ∼28–37 nm. FE-SEM confirmed the homogeneous and well defined surface morphology of the synthesized samples. FT-IR study showed the main absorption bands corresponding to the spinel structure those arose due to the tetrahedral and octahedral stretching vibrations. Cation distribution was estimated using XRD data. Hysteresis measurements revealed that the saturation magnetization decreased with increase in Cu²⁺ substitution. Magnetic environment of ⁵⁷Fe in Cu-doped cobalt ferrite was investigated by using Mössbauer spectroscopy. Mössbauer study evidenced the ferrimagnetic behavior of the synthesized samples.     

Effect of NaOH Concentration and Adding Sequences on Structural and Magnetic Properties of Ni<Subscript>0.4</Subscript>Co<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanopowders Prepared Via Co-precipitation Route

Ni_0.4Co_0.6Fe₂O₄ nanopowders were prepared via the co-precipitation route followed by annealing treatment. The structural and magnetic properties of the as-synthesized samples were determined by XRD, FT-IR, TG-DSC, and PPMS measurements, respectively. The XRD patterns indicated a single-phase cubic spinel structure for all the Ni-Co ferrite samples, regardless of adding sequences of the reactants or NaOH concentration. The analysis of the XRD patterns revealed that the enhancement in lattice constant with increasing NaOH concentration is related to the prevention of oxidization of Co²⁺ ions in the Ni-Co ferrite lattice. The FT-IR spectra indicated that samples prepared in the B process have fewer impurities than those prepared in the A process. The enhancement in saturation magnetization with the increase in sodium hydroxide concentration could be attributed to the strengthening of super-exchange interaction between A and B sublattices, due to replacements of Co³⁺ ions (magnetic moment of 0 μ _B) by Co²⁺ ions (magnetic moment of 3 μ _B) at B sublattices. The obvious increase in the coercivity field with the increase in concentration of NaOH solutions can be interpreted in terms of enhancement of magneto-crystalline anisotropy that originated from gradual substitutions of Co³⁺ ions with Co²⁺ ions at the octahedral sites.     

Structural and Magnetic Properties of Cobalt and Copper Ions Mixed Nickel Ferrite Nanoparticles

Co²⁺ and Cu²⁺ ions mixed nickel ferrite nanoparticles were synthesized by sol-gel auto combustion method. XRD patterns revealed the existence of a single-phase cubic spinel structure. The average grain size estimated from XRD patterns was found to be from 42 to 56 nm. VSM study indicates increase in saturation magnetization and decrease in coercivity. FE-SEM images exhibit particles with spherical shape and size ranges from 37 to 79 nm. The two main metal ion vibrations of ferrites were observed in FT-IR spectra.     

Hydrothermal formation of Ni-Zn ferrite from heavy metal co-precipitates

The hydrothermal synthesis of Ni-Zn ferrite from simulated wastewater containing Ni²⁺ and Zn²⁺ ions has been studied. The influence of co-precipitation order, the existence of Na⁺ in suspension, the hydrothermal reaction time and temperature on the composition, morphology and saturation magnetization (_s) of the hydrothermal products is reported. Adding the simulated wastewater to the NaOH solution can prevent the formation of -Fe₂O₃ in the Ni-Zn ferrite. Increasing the hydrothermal reaction time improved the magnetization of the Ni-Zn ferrite, while the influence of temperature, stirring intensity and Na⁺ in suspension on the hydrothermal formation of ferrite were not obvious. Thermodynamic calculation indicated that under hydrothermal conditions (180–240°C), the order of chemical stability is as follows: NiFe₂O₄ > Fe₂O₃ > Na₂Fe₂O₄. The high Gibbs formation energy of Na₂Fe₂O₄ prevented the incorporation of Na⁺ into the ferrite lattice.     

Influence of synthesis variables on the properties of barium hexaferrite nanoparticles

Barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were synthesized by sol–gel auto-combustion route. Prepared samples were sintered at 950 and 1100 °C with Fe³⁺/Ba²⁺ = 12 and 20 mol ratio. The formation mechanism of barium hexaferrite was investigated by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. In addition, the effect of temperature and Fe³⁺/Ba²⁺ mole ratio on BaFe₁₂O₁₉ formation and magnetic properties, and the effect of increasing the Fe³⁺/Ba²⁺ upon gel ignition and subsequent phase development were investigated. Finally the magnetic behavior was monitored with VSM. DSC studies showed that pure barium hexaferrite phase was formed from maghemite (γ-Fe₂O₃), without the formation of hematite (α-Fe₂O₃). Also, XRD results confirmed the formation of barium hexaferrite phase in non stoichiometric Fe/Ba ratio. VSM results showed that the saturation magnetization was decreased and coercivity increased with decreasing the grain size.     

Investigation on the Effects of Milling Atmosphere on Synthesis of Barium Ferrite/Magnetite Nanocomposite

In this research, barium ferrite /magnetite nanocomposites synthesized via a mechano-chemical route. Graphite was used in order to reduce hematite content of barium ferrite to magnetite to produce a magnetic nanocomposite. The effects of processing conditions on the powder characteristics were investigated by XRD, VSM, and HRTEM techniques. XRD results revealed that milling under air and argon atmospheres resulted in the appearance of Fe₃O₄ peaks beside BaFe₁₂O₁₉ peaks after 15 and 20 hrs milling, respectively. The intensity of Fe₃O₄ peaks in the XRD patterns increased by increasing the milling time. VSM studies revealed that saturation magnetization of the 40-hrs milled samples under air and argon atmospheres was 31.25 and 36.42 emu/g, respectively. This difference might be due to more Fe₃O₄ content in the latter sample. By annealing of the 40-hrs milled sample in air, saturation magnetization increased to 139.12 emu/g.     

Influence of the presence of Fe2+ ion in nickel-zinc ferrite

The presence of small amounts of Fe²⁺ ion in nickel zinc ferrite significantly influences some of its magnetic properties. The lattice parameter increases slightly and the increase Δa is independent ofx. The variation of magnetization with zinc concentration is explained on the basis of the Yafet-Kittel model. Increase in the Néel temperature on Fe²⁺ substitution in Zn _x Ni_1-x Fe₂O₄ is remarkable. This has been explained on the basis of a four sublattice model. Our analysis shows thatJ _AB (d ⁵-d ⁵) interaction is most affected. The influence of Fe²⁺ ions on the relaxation processes in the Mössbauer line shapes of Ni-Zn ferrite is also investigated and is compared with Cu²⁺ doped Ni-Zn ferrite.     

Mechanochemically activated synthesis of nanostructured NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Powdery NiFe₂O₄ has been obtained by mechanothermal treatment. Nickel and iron hydroxides are used as initial compounds. For comparison the initial compounds are calcinated without mechanical treatment (samples obtained by direct heating). The characterization of the samples is carried out by XRD analysis and Mössbauer spectroscopy. It is established that single phase NiFe₂O₄ is formed after mechanical activation (5 h) and calcination at 773 K. The ferrite synthesized at this temperature contains a smaller quantity of Fe³⁺ ions in tetrahedral position (31%) than is the case of conventional nickel ferrite (50%). The number of tetrahedrally coordinated iron ions increases with enhancement of the synthesis temperature, approaching the distribution of the tetrahedral and octahedral positions typical of conventional NiFe₂O₄. The samples obtained by direct heating contain unreacted NiO and α-Fe₂O₃ even after calcinations at 1073 K.     

Hysteresis analysis of Co-Ti substituted M-type Ba-Sr hexagonal ferrite

The magnetic, crystallographic properties and grain morphology of synthesized Ba_0.5Sr_0.5Co_xTi_xFe_{(12 − 2x)}O₁₉ ferrite have been investigated by XRD, SEM and VSM. XRD and SEM confirm M-type hexagonal crystal structure. X-ray diffraction indicates expansion of hexagonal unit cell with substitution of Co²⁺ and Ti⁴⁺ ions. The microstructure governs increase in density and intergrain connectivity with substitution. The preferential site occupancy of substituted Co²⁺ and Ti⁴⁺ ions results in rapid decline of anisotropy field, hysteresis loops also revealed same effect of substitution. Coercivity and remanence magnetization can be easily controlled by varying substitution while maintaining high saturation magnetization, making it useful for recording media.     

Effect of Ho3+ substitution on the cation distribution,crystal structure and magnetocrystalline anisotropy of nanocrystalline cobalt ferrite

Ho³⁺ ion-substituted nanocrystalline cobalt ferrite materials with the chemical formula CoFe_{2? x} Ho _x O₄ for x?=?0.0, 0.025, 0.05, 0.075 and 0.1 have been synthesised by standard citrate precursor method. Crystal structure and phase purity have been studied by powder X-ray diffraction (XRD) method by employing Rietveld refinement technique. The distribution of cations between the tetrahedral site (A-site) and octahedral site (B-site) has been estimated by Rietveld analysis. The refinement result shows that Ho³⁺ ion has a strong preference for octahedral sites (B-sites). The lattice constants decrease with the Ho³⁺ concentration up to x?=?0.05. Crystallite size decreases with the Ho³⁺ concentration. The magnetic hysteresis loop measurements have been carried out at room temperature using a vibrating sample magnetometer (VSM) over a field range of ±2?T. The magnetisations in saturation have been analysed by employing the ‘law of approach (LA)’ technique. The magnetocrystalline anisotropy constant and saturation magnetisation are found to decrease with the Ho³⁺ concentration up to x?=?0.05. The coercivity decreases with the Ho³⁺ concentration. The vibrational modes of the octahedral and tetrahedral metal complex in the sample have been carried out using Fourier transform infrared spectroscopy (FT-IR). The FT-IR spectra of the samples have been analysed in the wave number range of 350–1000?cm^?1. We have observed two prominent absorption bands which are assigned to tetrahedral and octahedral metal complexes. The elemental analysis has been carried out using energy dispersive spectroscopy (EDS) with the help of field emission scanning electron microscope (FE-SEM) and the results reveal that, elements are as per the stoichiometric ratio in all the samples.     

Synthesis of chemically coprecipitated hexagonal strontium-ferrite and its characterization

Highly uniform submicrometre size particles of hexagonal strontium ferrite (SrFe₁₂O₁₉) have been synthesized by chemical coprecipitation technique at pH ⋍ 13. Chemical coprecipitation technique has helped in bringing down the ferritization temperature from 1300 to 925° C which is revealed by DTA-TG and XRD studies. Reproducible uniform single domain particle size and its distribution has been observed by scanning electron microscopy. X-ray and Mossbauer studies have identified single phase ferrite with Fe³⁺ ions occupying the proper crystallographic sites. The performance parameters of the sintered isotropic strontium ferrite magnets have proved to be superior by about 20% over the ferrites prepared by conventional ceramic technique.     

In Situ Synthesis of Silica-Coated Magnetite Nanoparticles by Reverse Coprecipitation Method

Silica-coated magnetite nanoparticles were synthesized by reverse coprecipitation of Fe²⁺ and Fe³⁺ with sodium hydroxide in the presence of sodium silicate solution. Effect of reaction conditions and various amounts of sodium silicate solution on the powder particle characteristics was investigated by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), laser particle size analyzer (LPSA), streaming current potential and vibrating sample magnetometer (VSM) techniques. Also, stability of silica-coated magnetite nanoparticles in the acidic condition has been studied by titration method. FT-IR results revealed that silica chemisorbed on the surface of magnetite nanoparticles by Fe?CO?CSi bonds. Analysis of the XRD patterns confirmed the formation of magnetite having spinel structure in the presence of sodium silicate solution. FE-SEM micrographs revealed that the mean particle size of spherical magnetite decreased from 50 to less than 25?nm by adding sodium silicate solution. Agglomeration declined when the volume ratio of sodium silicate/sodium hydroxide was 0.1. This was attributed to the coating of magnetite nanoparticles by silica. Coating of magnetite by silica prevents the formation of hydrogen bondings between magnetite and water molecules. Further increase in the sodium silicate concentration revealed a reverse effect.     

Photoluminescence properties of β-Ga2O3:Tb nanofibers prepared by electrospinning

One-dimensional Tb³⁺-doped β-Ga₂O₃ nanofibers were prepared by a simple and cost-effective electrospinning process. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Raman technique, and photoluminescence (PL) were used to characterize the electrospun nanofibers. FE-SEM results indicated that the diameters all of the nanofibers ranged from 100 to 300 nm, and the lengths of nanofibers reached up to several millimeters. The XRD and Raman results showed that the Ga₂O₃ phase belongs to the monoclinic phase. Under ultraviolet excitation, the β-Ga₂O₃:Tb³⁺ samples showed green emission with the strongest peak at 550 nm, corresponding to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The luminescence intensity had been further studied as a function of the doping concentration of Tb³⁺ in the β-Ga₂O₃ samples.     

Non-stoichiometry of lithium-copper ferrites - I - spectrophotometric characterization (γ, X-ray,UV-vis IR)

In the heat-treatment under nitrogen of spinel type lithium-copper ferrite Li_0,25Cu_0,5Fe_2,25O₄, the oxygen loss involves the precipitation of CuFeO₂ and the formation of a non-stoichiometric ferrimagnetic phase. Fe²⁺ ions are revealed in this spinel phase by different spectrometric analyses (γ, X, UV-vis IR).     

Irradiation induced texturing in the Mg0.95Mn0.05Fe2O4 ferrite thin film

We present a study on the effect of swift heavy ions irradiation on the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ ferrite thin film grown by pulsed laser deposition technique. X-ray diffraction (XRD) pattern of the as-deposited film reveals a cubic spinel structure with an intermediate phase of α-Fe₂O₃. This impurity phase completely dissolves upon irradiation with 200 MeV Ag¹⁵⁺-ions and it exhibits a strong crystallographic texture along the (440) plane. The magnetization values start increasing systematically with irradiation at lower fluence values, whereas decrease for higher one. This decrease in magnetic signal can be attributed to partial amorphization caused by irradiation in agreement with XRD and atomic/magnetic force microscopic images.     

Synthesis, structural and magnetic characterization of iron-zinc-borate glass ceramics containing nanocrystalline zinc ferrite

Two different glass ceramics with the composition of the (Fe₂O₃)_x·(B₂O₃)_(60−x)·(ZnO)₄₀, where x = 12.5 and 15 mol%, have been synthesized using the melt-quench method. The X-ray diffraction (XRD) patterns show the presence of nanometric zinc ferrite (ZnFe₂O₄) crystals, with spinel structure, in a glassy matrix after cooling from melting temperature. The estimated amount of crystallized zinc ferrite varies between 16 and 35%, as a function of the chemical composition. Glass transition (T_g), crystallization (T_p) and melting (T_m) temperatures were determined by differential thermal analysis (DTA) investigations. Fourier transform infrared (FTIR) data revealed that the BO₃ and BO₄ are the main structural units of these glass ceramics network. FTIR spectra of these samples show features at characteristic vibration frequencies of ZnFe₂O₄. Electron paramagnetic resonance (EPR) measurements show the presence of isolated Fe³⁺ ions predominantly situated in rhombic vicinities and as well as the Fe³⁺ species interacting by dipole–dipole interaction or to their superexchange coupled pairs in clustered formations. The magnetic properties of the studied glass ceramics were investigated by vibrating sample magnetometer (VSM). From the magnetization curves for glass ceramic containing 15 mol% Fe₂O₃ it was found that the nanoparticles exhibit ferromagnetic interactions combined with superparamagnetism with a blocking temperature, T_B. For studied samples the hysteresis is present. The coercive field is dependent on composition and magnetic field being around 0.05 μ_B/f.u for measurements performed in maximum 0.4 T.     

Optical and structural investigations on iron-containing phosphate glasses

The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain non-toxic compounds related to environment. The oxide system Li₂O?CMgO?C(CaO)?CAl₂O₃?CP₂O₅?C(FeO/Fe₂O₃) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV?Cvis?CNIR (ultraviolet?Cvisible?Cnear infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 °C. UV?Cvis?CNIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe²⁺/Fe³⁺ species. TG analysis made in the 20?C1000 °C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 °C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe³⁺ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe²⁺ and Fe³⁺, both in octahedral coordination symmetry and a clustering process supported by only Fe³⁺ ions.     

Mn3O4 Nanoparticle Synthesis via Ionic Liquid-Assisted Route

Via the green chemistry route, a new class of Mn₃O₄ nanoparticles has been synthesized using 1-n-butyl-3-methylimidazolium trifluoromethane sulfonate [BMIM][TfO] ionic liquid, which serves as a capping agent. The thermal behavior, phase structure, morphology, and magnetic properties of the samples are characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), and Vibrating sample magnetometer (VSM) studies. The phase-pure Mn₃O₄ nanocrystals with 40-nm narrow particle size distribution are obtained with the significant influence of ionic liquid. The synthesized Mn₃O₄ nanoparticles show the superparamagnetic behavior.