Structure and magnetic properties of Co–Ni–Li ferrites synthesized by citrate precursor method

Nanoparticles of Co_0.5Ni_0.5−2xLi_xFe_2+xO₄ with x ranging from 0.00 to 0.25 in steps of 0.05 were prepared by using citrate precursor method. The microstructure and the magnetic properties of the as-prepared nanosamples and the effect of increasing Li¹⁺ ions on their physical properties were studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), particle size analyzer (PSA), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM) were used to investigate the samples. The XRD analysis confirmed the cubic spinel phase formation of the prepared samples, while TEM images and PSA ensure the nanostructural features of them. The FTIR spectra reveal the presence of two prominent absorption bands v₁ and v₂ in the range of 600 and 400 cm⁻¹ which are usually attributed to the tetrahedral and octahedral complexes of the spinel lattice, respectively. The change of v₂ gradually towards lower frequency and the slightly change of v₁ were explained depending on the effect of increasing Li¹⁺ content on the bond length of B-site metal ions and the spin canting of A-site metal ions, respectively. Saturation magnetization and remnant magnetization were found to increase with adding Li¹⁺ ions up to x=0.15 and then to decrease again, while coercivity decreases monotonically by increasing Li¹⁺ ions. The change in magnetic properties by adding Li¹⁺ ions is explained as to be dependent on many factors such as crystallite size, measured density, porosity, expected cation distribution, A–B exchange interactions, and magnetocrystalline anisotropy.     

Structural and magnetic properties of nano-crystalline Ni–Zn ferrites synthesized using egg-white precursor

Nano-crystalline nickel–zinc ferrites of different compositions; Ni_1−xZn_xFe₂O₄ (x=0.0–1.0) were prepared by a precursor method involving egg-white and metal nitrates. An appropriate mechanism for the egg-white-metal complexation was suggested. Differential thermal analysis-thermogravimetry, X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer and AC-magnetic susceptibility measurements were carried out to investigate chemical, structural and magnetic aspects of Ni–Zn ferrites. XRD confirmed the formation of spinel cubic structure. The average crystallite size was calculated using line broadening in XRD patterns. Structural parameters like lattice constant, X-ray density, bond lengths and inter-cationic distance were determined from XRD data. TEM showed agglomerated particles with average size agreed well with that estimated using XRD. FT-IR spectra confirm the formation of spinel structure and further lends support to the proposed cation distribution. Zn-content was found to have a significant influence on the magnetic properties of the system. The changes in the magnetic properties can be attributed to the influence of the cationic stoichiometry and their occupancy in the specific sites.     

High-resistivity nickel–zinc ferrites by the citrate precursor method

Nickel–zinc ferrites of different compositions, Ni_1−xZn_xFe₂O₄ with x=0.2, 0.35, 0.5 and 0.6, have been prepared by a precursor method involving citrate precursors of the concerned metals and mixing them in solution state. Resistivity has been studied as a function of composition and sintering temperature. It is observed that NiZn ferrites prepared by this method have resistivity ⩾10⁸ Ω cm which is higher by atleast two orders of magnitude than that reported (⩽10⁶ Ω cm) for ferrites prepared by the conventional ceramic method. This is attributed to better purity as well as better compositional and microstructural control achievable by the citrate method. High resistivity makes these ferrites suitable particularly for high-frequency applications where eddy current losses are required to be low.     

Effect of nanoparticles on the magnetic properties of Mn–Zn soft ferrite

In this paper, the effect of nanostructures on the magnetic properties like the specific saturation magnetization (σ_S) and the coercivity (H_C) for Mn_0.4Zn_0.6Fe₂O₄ ferrite prepared by the co-precipitation method has been presented. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanoparticles, and that the average size of these nanoparticles calculated with the Scherrer formula depends upon the sintering temperature. When the sintering temperature is increased from 500 to 900 °C, the average nanoparticle diameter varies from 19.3 to 36.4 nm. The nanoparticle phase is further confirmed by scanning electron microscopy (SEM). Both results are found to be in good agreement. The magnetic properties are explained on the basis of the single-domain and multi-domain theory.     

Influence of manganese substitution and annealing temperature on the formation,microstructure and magnetic properties of Mn–Zn ferrites

The effects of annealing temperature and manganese substitution on the formation, microstructure and magnetic properties of Mn_xZn_1−xFe₂O₄ (with x varying from 0.3 to 0.9) through a solid-state method have been investigated. The correlation of the microstructure and the grain size with the magnetic properties of Mn–Zn ferrite powders was also reported. X-ray diffraction (XRD), a scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM) were utilized in order to study the effect of variation of manganese substitution and its impact on crystal structure, crystalline size, microstructure and magnetic properties of the ferrite powders formed. The XRD analysis showed that pure single phases of Mn–Zn ferrites were obtained by increasing the annealing temperature to 1200–1300 °C. Increasing the annealing temperature to ?1300 °C led to abnormal grain growth with inter-granular pores and this led to a decrease in the saturation magnetization. Moreover, an increase in the Mn²⁺ ion substitution up to x=0.8 increased the lattice parameter of the formed powders due to the high ionic radii of the Mn²⁺ ion. Mn–Zn ferrites phases were formed and the positions of peaks were shifted by substituting manganese. The average crystalline size was increased by increasing the annealing temperature and decreased by increasing the substitution by manganese up to 0.8. The average crystalline size was in the range 95–137.3 nm. The saturation magnetization of the Mn–Zn-substituted ferrite powders increased continuously with an increase in the Mn concentration up to 0.8 at annealing temperatures of 1200–1300 °C. Further increase of Mn substitution up to 0.9 led to a decrease of saturation magnetization. The saturation magnetization increased from 17.3 emu/g for the Mn_0.3Zn_0.7Fe₂O₄ phase particles produced to 59.08 emu/g for Mn_0.8Mn_0.2Fe₂O₄ particles.     

Effect of ethylene carbonate concentration on structural and electrical properties of PEO–PMMA polymer blends

Polyethylene oxide–polymethyl methacrylate (PEO–PMMA) polymer blend electrolyte system complexed with silver salt having different ethylene carbonate (EC) concentrations was prepared using solution cast technique. Complex formation and change in structural and microstructural properties have been studied by X-ray diffraction, Fourier transform infrared, and scanning electron microscopy analysis. The thermal properties of polymer films have been examined by the differential scanning calorimetry technique. Addition of plasticizer is observed to lower melting temperature. Electrical response of polymer films has been measured as a function of EC concentration and temperature using complex impedance spectroscopy. Complex impedance data are used to analyze the conductivity, permittivity, and modulus formalism to understand the conduction mechanism. The temperature dependence of electrical conductivity of polymer electrolytes shows a sudden rise at the melting temperature of PEO.     

Ni–Zn–Sm nanopowder ferrites: Morphological aspects and magnetic properties

Ni–Zn ferrites have been widely used in components for high-frequency range applications due to their high electrical resistivity, mechanical strength and chemical stability. Ni–Zn ferrite nanopowders doped with samarium with a nominal composition of Ni_0.5Zn_0.5Fe_2−xSm_xO₄ (x=0.0, 0.05, and 0.1 mol) were obtained by combustion synthesis using nitrates and urea as fuel. The morphological aspects of Ni–Zn–Sm ferrite nanopowders were investigated by X-ray diffraction, nitrogen adsorption by BET, sedimentation, scanning electron microscopy and magnetic properties. The results indicated that the Ni–Zn–Sm ferrite nanopowders were composed of soft agglomerates of nanoparticles with a high surface area (55.8–64.8 m²/g), smaller particles (18–20 nm) and nanocrystallite size particles. The addition of samarium resulted in a reduction of all the magnetic parameters evaluated, namely saturation magnetization (24–40 emu/g), remanent magnetization (2.2–3.5 emu/g) and coercive force (99.3–83.3 Oe).     

Influence of CuO and sintering temperature on the microstructure and magnetic properties of Mg–Cu–Zn ferrites

The synthesis of a series of Mg–Cu–Zn ferrites with the substitution of Cu for Mg has been obtained by solid-state reaction method. Microstuctural and structural analyses were carried out using a scanning electron microscope and X-ray diffraction (XRD), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. Microstructural analyses indicate that CuO influences the microstructure of the ferrites by the formation of liquid phase during sintering. The grain size significantly increases with increasing copper content. Exaggerated grain growth is observed for the samples of x=0.25–0.35. The initial magnetic permeability (μ′) increases sharply with increasing concentration of Cu ions. This increase in μ′ is explained with the grain growth mechanism and enhanced densification of the ferrites. The resonance frequency of all the samples shifts toward the lower frequency as the permeability increases with Cu content. Sintering temperature T_s also affects the densification, grain growth and initial magnetic permeability of the samples.     

Enhanced structural and magnetic properties of microwave sintered Li–Ni–Co ferrites prepared by sol–gel method

The properties of lithium ferrites are very sensitive to chemical composition, synthesis method, and sintering techniques. Li–Ni–Co ferrites with compositional formula Li_(0.45-0.5x)Ni_(0.1)Co_xFe_(2.45-0.5x)O_4, where 0.00 ≤ x ≤ 0.1 in steps of 0.02 were prepared by chemical sol–gel method and sintered by microwave sintering technique. The x-ray diffraction patterns confirmed the formation of single phase with spinel structure in all the samples. The structural parameter viz.lattice constant, crystallite size, and x-ray density for these samples were studied and compared with those measured from samples of similar composition prepared by the sol–gel method and sintered by conventional sintering technique. Enhancement in the magnetic properties like Curie temperature, hysteresis parameters was observed by employing sol–gel synthesis combined with microwave sintering. The results obtained and mechanisms involved are discussed in the paper.     

Influence of Ag doping on structural and optical properties of ZnO thin films synthesized by the sol–gel technique

Thin films of Ag–ZnO samples deposited on glass substrates with a different percentage of Ag content (1, 2, and 3 at%) were synthesized, at room temperature, by a dip-coating sol-gel method. The obtained samples are hexagonal wurtzite structure. The average grain size of deposits is about 5 nm. Up to 3 at%, c-axis lattice parameter shifts toward a higher value, which indicates that silver atoms replace Zn atoms in the crystal lattice. As shown by the DRX spectra, growth rate in the (101) direction is favored by the presence of silver ions in the ZnO. The layers present a homogeneous crystallites distribution, as we can remark it on SEM micrographs and exhibit a very low roughness according to AFM images. The entire samples exhibit a transmission value greater than 80 %, in the visible region, while the maximum is obtained for those doped at 2 at%. Energy band varies between 3.15 eV and 3.25 eV. The wider gap obtained is that of the ZnO layer doped with 2 at%. It is worth noting a strong UV emission observed on PL spectrum, performed at very low temperature (liquid nitrogen temperature), for silver doped ZnO compared to that of pure ZnO.     

Influence of Al doping on electrical properties of Ni–Cd nano ferrites

We have reported the structural and electrical properties of nano particles of Al doped Ni_0.2Cd_0.3Fe_2.5O₄ ferrite using X-ray diffraction, dielectric spectroscopy and impedance spectroscopy at room temperature. XRD analysis confirms that the system exhibits polycrystalline single phase cubic spinel structure. The average particle size estimated using Scherrer formula for Lorentzian peak (3 1 1), has been found 5(±) nm. The results obtained show that real (ε′), imaginary (ε″) part of the dielectric constant, loss tangent (tan δ), and ac conductivity (σ_ac) shows normal behaviour with frequency. The dielectric properties and ac conductivity in the samples have been explained on the basis of space charge polarization according to Maxwell–Wagner two-layer model and the Koop’s phenomenological theory. The impedance analysis shows that the value of grain boundary impedance increases with Al doping. The complex impedance spectra of nano particles of Al doped Ni–Cd ferrite have been analyzed and explained using the Cole–Cole expression.     

Finite size effect and influence of temperature on electrical properties of nanocrystalline Ni–Cd ferrites

Electrical conductivity and dielectric measurements have been investigated for four different average grain sizes ranging from 3 to 7 nm of nanocrystalline Ni_0.2Cd_0.3Fe_2.5−xAl_xO₄ (0.0 ⩽ x ⩽ 0.5) ferrites. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of the Al doped Ni–Cd ferrites. The analysis of data shows only one semi-circle corresponding to the grain boundary volume suggesting that the conduction mechanism takes place predominantly through grain boundary volume in the studied samples. The variation of impedance properties with temperature and composition has been studied in the frequency range of 120 Hz–5 MHz between the temperatures 300–473 K. The hopping of electrons between Fe³⁺ and Fe²⁺ as well as hole hopping between Ni³⁺ and Ni²⁺ ions at octahedral sites are found to be responsible for conduction mechanism. The dielectric constant and loss tangent (tan δ) are found to decrease with increasing frequency, whereas they increase with increasing temperature. The dielectric constant shows an anomalous behavior at selected frequencies, while the temperature increases, which is expected due to the generation of more electrons and holes as the temperature increases. The behavior has been explained in the light of Rezlescu model.     

Mössbauer and magnetic studies of nanocrystalline zinc ferrites synthesized by microwave combustion method

Zinc ferrite nano-crystals were synthesized by a microwave assisted combustion route with varying the urea to metal nitrates (U/N) molar ratio The process takes only a few minutes to obtain Zinc ferrite powders. The Effect of U/N ratio on the obtained phases, particle size, magnetization and structural properties has been investigated. The specimens were characterized by XRD, Mössbauer and VSM techniques. The sample prepared with urea/metal nitrate ratio of 1/1 was a poorly crystalline phase with very small crystallite size. A second phase is also detected in the sample. The crystallite size increases while the second phase decrease with increasing the urea ratio. The saturation magnetization and coercivity of the as prepared nano-particles changed with the change of the U/N ratio. The powder with the highest U/N ratio showed the presence of an unusually high saturation magnetization of 16 emu/g at room temperature. The crystallinity of the as prepared powder was developed by annealing the samples at 700 ^°C and 900 ^°C. Both the saturation magnetization (Ms) and the remnant magnetization (Mr) were found to be highly dependent upon the annealing temperature. Mössbauer studies show magnetic ordering in the powder even at room temperature. The Mössbauer and the magnetic parameters of this fraction are different from the standard values for bulk zinc ferrite.