Effects of precursor types of Fe and Ni components on the properties of NiFe2O4 powders prepared by spray pyrolysis

The effects of the precursor types of Ni and Fe components on the morphology, mean size, and magnetic property of NiFe₂O₄ powders prepared by spray pyrolysis from the spray solution, with citric acid were studied. The precursor powders with hollow and thin wall structure turned to the nano-sized NiFe₂O₄ powders after post-treatment at a temperature of 800 °C. The nickel ferrite powders obtained from the spray solution with ferric chloride had nanometer sizes and narrow size distributions irrespective of the types of nickel precursor. The nickel ferrite powders obtained from the spray solution with ferric nitrate and nickel chloride also had nanometer size and narrow size distribution. The saturation magnetizations of the NiFe₂O₄ powders changed from 37 to 42 emu/g according to the types of the Fe and Ni precursors. The saturation magnetizations of the NiFe₂O₄ powders increased with increasing the Brunauer-Emmett-Teller (BET) surface areas of the powders.     

Magnetic and Gas Sensing Property of Nanosized NiFe2O4 Powders Synthesized by Pulsed Wire Discharge

Nickel ferrite (NiFe₂O₄) powders were synthesized by pulsed wire discharge method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses show that only nickel ferrite spinel and no other phase was observed in the powders. Mean size of the obtained particles strongly depended on the oxygen pressure: the higher oxygen pressure corresponds to larger powder size, as determined by Brunauer–Emmet–Teller (BET). The room temperature saturation magnetization of the synthesized powders was 42–46 emu/g depending on the powder size. These powders also showed high chlorine sensitivity at about 280–360°C, and a good linear sensitivity with chlorine concentration.     

Microwave-induced combustion synthesis of Ni–Zn ferrite powder and its characterization

Ni–Zn ferrite powders were successfully synthesized by microwave-induced combustion process. The process takes only a few minutes to obtain calcined Ni–Zn ferrite powders. The resultant powders were investigated by XRD, SEM, VSM, TG/DTA and surface area measurements. The as-received product shows the formation of cubic ferrite with saturation magnetization (M_s)≈23 emu/g, whereas upon annealing at 850°C for 4 h, the saturation magnetization (M_s) increased to ≈52 emu/g.     

Effect of zinc substitution on magnetic and electrical properties of nanocrystalline nickel ferrite synthesized by refluxing method

Nanocrystalline Nickel ferrite (NiFe₂O₄) and Zn substituted nickel ferrite (NiZnFe₂O₄) have been synthesized by the refluxing method. These ferrites were characterized by XRD, TEM, Mossbauer spectroscopy and VSM in order to study the effect of zinc substitution in nickel ferrite. XRD diffraction results confirm the spinel structure for the prepared nanocrystalline ferrites with an average crystallite size of 14-16 nm. Lattice parameter was found to increase with the substitution of Zn²⁺ ions from 8.40 Å to 8.42 Å. TEM images confirmed average particle size of about 20 nm and indicates nanocrystalline nature of the compounds. A shift in isomeric deviation with the doublet was observed due to the influence of Zn substitution in the nickel ferrite. The Zn content has a significant influence on the magnetic behavior and electrical conductivity of NiFe₂O₄. Saturation magnetization drastically increased whereas room temperature electrical conductivity decreased due to the addition of Zn content in NiFe₂O₄, indicating super magnetic material with lesser coercivity.     

Finite size effects on the structural and magnetic properties of sol–gel synthesized NiFe2O4 powders

Nanoparticles of nickel ferrite have been synthesized by the sol–gel method and the effect of grain size on its structural and magnetic properties have been studied in detail. X-ray diffraction (XRD) studies revealed that all the samples are single phasic possessing the inverse spinel structure. Grain size of the sol–gel synthesized powders has been determined from the XRD data and the strain graph. A grain size of 9 nm was observed for the as prepared powders of NiFe₂O₄ obtained through the sol–gel method. It was also observed that strain was induced during the firing process. Magnetization measurements have been carried out on all the samples prepared in the present series. It was found that the specific magnetization of the nanosized NiFe₂O₄ powders was lower than that of the corresponding coarse-grained counterparts and decreased with a decrease in grain size. The coercivity of the sol–gel synthesized NiFe₂O₄ nanoparticles attained a maximum value when the grain size was 15 nm and then decreased as the grain size was increased further.     

Hyperfine characterization of the crystallization of nanocrystalline NiFe2O4 from the amorphous silica gel

Nanocrystalline NiFe₂O₄ was in‐situ prepared in amorphous silica using tetramethylor‐thosilicate and nickel (iron) nitrate hydrate as the starting materials in a sol‐gel reaction. The magnetic nanocrystals in the amorphous silica glasses grew slowly with increasing temperature. Above 600^○C, nickel ferrite nanoparticles began to precipitate from the amorphous silica matrix. Mössbauer spectroscopy of the nanocomposites suggested that in the silica glasses, Fe ions were present exclusively as Fe³⁺ in octahedral coordination, and the chemical environment of the Fe³⁺ ions appeared to remain unchanged until the crystallization of nickel ferrite nanocrystals. The formation of NiFe₂O₄ nanocrystals was the result of partial transformation of the FeO₆ octahedra to FeO₄ tetrahedra. The nanocrystalline NiFe₂O₄ are characterized by super‐paramagnetic behaviour at room temperature.     

Chemical synthesis of spinel nickel ferrite (NiFe2O4) nano-sheets

The present investigation is related to the deposition of single-phase nano-sheets spinel nickel ferrite (NiFe₂O₄) thin films onto glass substrates using a chemical method. Nano-sheets nickel ferrite films were deposited from an alkaline bath containing Ni²⁺ and Fe²⁺ ions. The films were characterized for their structural, surface morphological and electrical properties by means of X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and two-point probe electrical resistivity techniques. The X-ray diffraction pattern showed that NiFe₂O₄ nano-sheets are oriented along (3 1 1) plane. The FT-IR spectra of NiFe₂O₄ films showed strong absorption peaks around 600 and 400 cm⁻¹ which are typical for cubic spinel crystal structure. Microstructural study of NiFe₂O₄ film revealed nano-sheet like morphology with average sheet thickness of 30 nm. The room temperature electrical resistivity of the NiFe₂O₄ nano-sheets was 10⁷ Ω cm.     

Nanostructural and magnetic studies of virtually monodispersed NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystals synthesized by a liquid–solid-solution assisted hydrothermal route

This study presents a comprehensively and systematically structural, chemical and magnetic characterization of ~9.5 nm virtually monodispersed nickel ferrite (NiFe₂O₄) nanoparticles prepared using a modified liquid–solid-solution (LSS) assisted hydrothermal method. Lattice-resolution scanning transmission electron microscope (STEM) and converged beam electron diffraction pattern (CBED) techniques are adapted to characterize the detailed spatial morphology and crystal structure of individual NiFe₂O₄ particles at nano scale for the first time. It is found that each NiFe₂O₄ nanoparticle is single crystal with an fcc structure. The morphology investigation reveals that the prepared NiFe₂O₄ nanoparticles of which the surfaces are decorated by oleic acid are dispersed individually in hexane. The chemical composition of nickel ferrite nanoparticles is measured to be 1:2 atomic ratio of Ni:Fe, indicating a pure NiFe₂O₄ composition. Magnetic measurements reveal that the as-synthesized nanocrystals displayed superparamagnetic behavior at room temperature and were ferromagnetic at 10 K. The nanoscale characterization and magnetic investigation of monodispersed NiFe₂O₄ nanoparticles should be significant for its potential applications in the field of biomedicine and magnetic fluid using them as magnetic materials.     

Study of gamma ray energy absorption and exposure buildup factors for ferrites by geometric progression fitting method

The gamma ray energy absorption and exposure buildup factors (EABF and EBF) were calculated for ferrites such as cobalt ferrite (CoFe₂O₄), zinc ferrite (ZnFe₂O₄), nickel ferrite (NiFe₂O₄) and magnesium ferrite (MgFe₂O₄) using five parametric geometric progression (G-P fitting) formula in the energy range 0.015–15.00?MeV up to the penetration depth 40 mean free path (mfp). The obtained data of absorption and exposure buildup factors have been studied as a function of incident photon energy and penetration depth. The obtained EABF and EBF data are useful for radiation dosimetry and radiation therapy.     

Effect of electromagnetic field strength on Ni0.35Zn0.65Fe2O4 as performed by combustion synthesis

Ni_0.35Zn_0.65Fe₂O₄ ferrite is prepared through combustion synthesis in the external electromagnetic field. The highest magnetic field strength for the experiment is 1.1 T. Reactions temperatures were monitored by infrared radiation thermometer, the synthesized ferrite prepared in different magnetic fields is analyzed by XRD, SEM, and VSM. The results indicate that the coercivity of ferrite gradually decrease with the increase of magnetization. When the magnetic field strength is 0.54 T, the saturation magnetization is improved up to 56.05 emu/g (42%) as compared to that of ferrite in zero magnetic field. Through SEM analysis of Ni_0.35Zn_0.65Fe₂O₄ ferrite, homogeneous grains of the crystal are observed. With the increase of external magnetic field, the ferrite grain improved. This paper also systematically explores the effect of the electromagnetic field on ferrite by combustion synthesis.     

Multiferroic behaviour of epitaxial NiFe2O4--BaTiO3 heterostructures

Multiferroic NiFe2O4 （NFO）-BaTiO3 （BTO） bilayered thin films are epitaxially grown on （001） Nb-doped SrTiO3 （STO） substrates by pulsed-laser deposition （PLD）. Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with （001）-orientation, i.e. （001）-NFO/（001）-BTO/substrate and （001）- BTO/（001）-NFO/substrate. Microstructure studies from x-ray diffraction （XRD） and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious magnetoelectric （ME） effect on coupling response.     

Microstructure characterization of mechanosynthesized nanocrystalline NiFe2O4 by Rietveld's analysis

Nanocrystalline nickel ferrite (NiFe₂O₄) is synthesized at room temperature by high-energy ball milling the stoichiometric mixture of (1:1 mol%) of NiO and α-Fe₂O₃ powders. The structural and microstructural evolution of NiFe₂O₄ caused by milling is investigated by X-ray powder diffraction. The relative phase abundance, particle size, r.m.s. strain, lattice parameter changes of different phases have been estimated employing Rietveld structure refinement analysis of X-ray powder diffraction data. Particle size and content (wt%) of both NiO and α-Fe₂O₃ phases reduce rapidly with increasing milling time and a significant amount of nanocrystalline NiFe₂O₄ is formed within 1 h of ball milling. Particle sizes of all the phases reduce to ∼10 nm within 5 h of milling and remain almost unchanged with increasing milling time up to 20 h. Lattice parameter of cubic NiO decreases linearly with increasing milling time, following the Vegard's law of solid-solution alloy. A continuous decrease in lattice parameter of cubic NiFe₂O₄ phase clearly suggests that smaller Ni atoms have occupied some of the vacant oxygen sites of ferrite lattice. Cation distribution both in octahedral and tetrahedral sites changes continuously with milling time and the normal spinel lattice formed at early stage of milling, transforms to inverse spinel lattice in the course of milling. High-resolution transmission electron microscope (HRTEM) micrographs of 11 h milled sample corroborates the findings of X-ray profile analysis.     

Nickel-induced magnetic behaviour of nano-structured α-Fe2O3, synthesised by facile wet chemical route

We report the synthesis of pristine and nickel containing iron oxide (α-Fe₂O₃) nanocrystallites by facile environmentally benign wet chemical process. The magnetic behaviour of the samples has been found to change progressively with nickel content. The Mössbauer spectra revealed the precipitation of secondary phase of nickel ferrite (NiFe₂O₄) at ～2?wt% nickel contents. The transmission electron micrographs together with asymmetric magnetic hysteresis loop have confirmed the formation of core–shell structure. The Morin temperature of nanostructured α-Fe₂O₃ as estimated by superconducting quantum interference device has been found to be 257, 245, 247 and 242?K at nickel content of 0, 1, 2 and 4?wt%, respectively. The similar trends of increase/decrease in Morin temperature have been noticed by Mössbauer analysis. Furthermore, below Morin temperature, the temperature range of coexisted antiferromagnetic and ferromagnetic states has been found to increase with increase in nickel content.     

Li0.5Fe2.5−xMnxO4 ferrite sintered from microwave-induced combustion

Li_0.5Fe_2.5−xMn_xO₄ (0≦x≦1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, ferric nitrate, manganese nitrate and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Mn-substituted lithium ferrite powders. The resultant powders annealed at 650 ^°C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the Mn content were strongly influenced the magnetic properties and Curie temperature of Mn-substituted lithium ferrite powder. As for sintered Li_0.5Fe_2.5−xMn_xO₄ specimens, substituting an appropriate amount of Mn for Fe in the Li_0.5Fe_2.5−xMn_xO₄ specimens markedly improved the complex permeability and loss tangent.     

Synthesis and magnetic characterization of nickel ferrite nanoparticles prepared by co-precipitation route

Magnetic nanoparticles of nickel ferrite (NiFe₂O₄) have been synthesized by co-precipitation route using stable ferric and nickel salts with sodium hydroxide as the precipitating agent and oleic acid as the surfactant. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of single-phase nickel ferrite nanoparticles in the range 8-28 nm depending upon the annealing temperature of the samples during the synthesis. The size of the particles (d) was observed to be increasing linearly with annealing temperature of the sample while the coercivity with particle size goes through a maximum, peaking at ∼11 nm and then decreases for larger particles. Typical blocking effects were observed below ∼225 K for all the prepared samples. The superparamagnetic blocking temperature (T_B) was found to be increasing with increasing particle size that has been attributed to the increased effective anisotropy energy of the nanoparticles. The saturation moment of all the samples was found much below the bulk value of nickel ferrite that has been attributed to the disordered surface spins or dead/inert layer in these nanoparticles.     

Structural and Magnetic Properties of NiFe2−2xSnxCuxO4

The substituted nickel ferrite (NiFe_2−2xSn_xCu_xO₄, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe³⁺ ions by Sn⁴⁺ and Cu²⁺ cations on the structural and magnetic properties of the ferrite was studied by means of ⁵⁷Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe₂O₄ adopts a fully inverse spinel structure of the type (Fe)[NiFe]O₄, Sn⁴⁺ and Cu²⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe_1−2xSn_xCu_x]O₄, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe_2−2xSn_xCu_xO₄ samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement.     

Preparation and magnetic studies of nickel ferrite nanoparticles substituted by Sn and Cu

The mixed ferrite systems, namely NiFe_2−2xSn_xCu_xO₄ (x=0, 0.1, 0.2, and 0.3) nanoparticles have been studied to understand their structural and magnetic parameters. The NiFe_2−2xSn_xCu_xO₄ nanoparticles were prepared by high energy ball milling (HEBM). The samples were characterized by the X-ray diffraction technique. All samples exhibited spinel structures. The crystalline size and internal strain were evaluated by XRD patterns using Williamson-Hall and Scherrer methods. Magnetic properties of the nanoparticles ferrite were studied by means of alternating gradient force magnetometry (AGFM) and Faraday balance.     

Preparation and characterization of NiFe2O4/NiO composite film via a single-source precursor route

NiFe₂O₄/NiO nanocomposite thin films have been successfully prepared through a facile route using nickel iron layered double hydroxide (NiFe-LDH) as a single-source precursor. This synthetic approach mainly involves the formation of NiFe-LDH film by casting the slurry of NiFe-LDH precursor on the α-Al₂O₃ substrate, followed by high-temperature calcination. The composition, microstructure and properties of the films were characterized in detail by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results indicate that NiFe₂O₄/NiO composite film was composed of granules with diameter less than 100 nm, and the thickness of the film was in the range 1-2 μm. The magnetization of the film can be tuned by alternating the Ni/Fe molar ratio of LDH precursor. In addition, the method developed should be easily extended to fabricate other MFe₂O₄/MO composite film systems with specific applications just by an appropriate combination of divalent/trivalent composition in the precursor of LDHs.     

Swift heavy ion-induced effects in Ce-doped nickel ferrite nanoparticles

Swift heavy ions of various energies are being used for material modifications. The induced modifications depend on the kind of defects produced during interaction of ions with the target material. In the present work, irradiation of 200 MeV Ag beam-induced effects in NiFe₂O₄ and NiCe_0.04Fe_1.96O₄ nanoparticles are studied at two different fluences, 2×10¹² and 1×10¹³ ions/cm². Nanoparticles of nickel ferrite and Ce-doped nickel ferrite were prepared by chemical route. X-ray diffraction pattern shows peaks corresponding to pure spinel structure in both the systems, NiFe₂O₄ and NiCe_0.04Fe_1.96O₄. The pristine as well as irradiated nanoparticles were characterized by high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, electron paramagnetic resonance spectroscopy (EPR) and vibrating sample magnetometer (VSM). Raman spectra show bands corresponding to spinel structure. After irradiation, the position of the bands does not change significantly for both samples. The widths corresponding to the same band in both the systems show opposite trend with fluence. VSM results show that after irradiation, the magnetization decreases from 40 to 32 A m²/kg for NiFe₂O₄ and from 39 to 31 A m²/kg for NiCe_0.04Fe_1.96O₄. EPR results show that after doping with Ce as well as irradiation, the EPR line width is reduced, making samples important for applications.     

The study of transition on NiFe2O4 nanoparticles prepared by co-precipitation/calcination

In this study, the NiFe₂O₄ nanoparticles have been prepared by co-precipitation and calcination process. Using a vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer of X-ray (EDX), and X-ray photoelectron spectroscopy (XPS), the samples obtained by co-precipitation and then by further calcination have been analyzed. The experimental results show that the precursor synthesized by co-precipitation is the composite of both amorphous FeOOH and Ni(OH)₂, but has no amorphous NiFe₂O₄. The results of both EDX and XPS revealed that the FeOOH species is wrapped up by Ni(OH)₂ species. In the calcination process, the amorphous composite is dehydrated and transformed gradually into crystalline NiFe₂O₄ nanoparticles, with the metal ions diffusing. The reaction is different from the one used to prepare other ferrite (e.g., CoFe₂O₄, MnFe₂O₄, Fe₃O₄, etc.) nanoparticles directly by co-precipitation. With increasing calcination temperature, the NiFe₂O₄ grains grow and the magnetization is enhanced.