Nanocrystalline Ni Zn Ferrites Research Articles

Experimental and theoretical investigations of the role of (Co–Ti) in the modification of the functional properties of nanocrystalline Ni–Zn ferrites

Experimental and theoretical investigations of the role of (Co–Ti) in the modification of the functional properties of nanocrystalline Ni–Zn ferrites

Tunable cationic distribution and structure-related magnetic and optical properties by Cr3+ substitution for Zn2+ in nanocrystalline Ni-Zn ferrites

We report a microwave-combustion synthesis and structure-related physical properties of Ni0.4Zn0.6−xCrxFe2O4 (0.0 ≤ x ≤ 0.6) nanocrystals in a study of effects by substitution among cations with different oxidation states, Cr3+ for Zn2+. High-quality nanocrystals with an average particle size of 26–33 nm and crystallite size ranged in 23–32 nm are revealed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Structural properties and cationic redistribution are studied by the XRD Rietveld analysis implying different preferences of Zn2+ and Cr3+ ions to occupy the tetrahedral and octahedral sites, respectively. Further characterization for the characteristic IR absorption bands, ionic valence states, chemical compositions and morphology have been performed by employing the Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and electron dispersive X-ray spectroscopy (SEM-EDX). XPS analysis indicates partial reduction of Fe3+ to Fe2+ and further confirms the estimated cationic distribution. UV–Vis absorbance measurements indicated a gradual decrease in the optical energy gap which implies the emergence of sub-band-gap energy levels by the Cr substitution. The magnetic properties were investigated by magnetization measurements showing highly soft magnetic behavior. The values and trend of the observed magnetic moment are consistent with the theoretically calculated magnetic moment based on cationic distributions estimated from the XRD and XPS. Ni-Zn-Cr spinel nanoferrites with soft magnetic properties, magnetization up to 106 emu/g and coercivity down to 70 Oe, tunable by cationic redistribution are introduced for high-frequency power applications.

Influence of Zn2+ doping towards the structural, magnetic, and dielectric properties of NiFe2O4 composite

The present work is aimed to study the changes in characteristics of nickel ferrites followed by the zinc doping and for that, the nanocrystalline Ni–Zn ferrites (Ni1−xZnxFe2O4: x = 0, x = 0.2 and x = 0.4) were prepared via sol–gel auto combustion method and by annealing at subsequent temperature. The physical characterization studies of the final composite provided that the lattice structure of Zn2+ substituted at Ni sites confirms for the single-phase ferrite with spinel structure got investigated at room temperature (RT) with functional, morphological as well as temperature-dependent magnetic and dielectric properties. The magnetic properties imply that the distribution of cations at the lattice sites suggests that the magnetization is getting increased with a decrease of temperature from RT to lower temperature in a field cooling process and is due to the strong dipolar magnetostatic interactions between the individual magnetic moments, which also affirms that the magnetization decreases with a decrease of Ni concentration. The coercively extracted from isothermal magnetization curves attributed to the single domain nature at RT. Further, the dielectric constant (e′) and dielectric loss (tan δ) are also examined and found to be strongly dependent on the function of frequency and temperature. The change in e′ and tan δ demonstrated that the dispersion due to the Maxwell–Wagner interfacial polarization and is in a good agreement with Koop’s theory.

Cation Distribution and Magnetic Properties of Gd+3-Substituted Ni-Zn Nano-ferrites

A series of Gd+3-substituted nanocrystalline Ni-Zn ferrites Ni1-xZnxGd0.1Fe1.9O4 (0 ≤ x ≤ 1) are prepared using a low-temperature citrate auto-combustion method. The cation distribution obtained using powder x-ray diffraction demonstrates an increase in hopping length between magnetic and Zn+2 ions. Cation–oxygen vibrations are identified by FTIR spectra. Effect of Zn+2 ion on the magnetic properties at room temperature is determined from the magnetic moment measured through a vibrating sample magnetometer. The magnetic moment and saturation magnetization obey Yafet–Kittel type magnetization with the highest saturation magnetization for x = 0.2 (≈ 54 emu/g). The low squareness ratio of the samples (0.25–0.12) confirms the uniaxial anisotropy.

The influence of Nd substitution in Ni–Zn ferrites for the improved microwave absorption properties

Nanocrystalline Ni–Zn ferrites with different neodymium contents (Ni0.5Zn0.5NdxFe2-xO4) were synthesized by sol-gel route combined with self-propagating combustion (SPC) method. The presence of surface functional groups, crystal structure and morphology of the samples were studied by FT-IR, XRD and SEM. The results show that the prepared samples are composed of spinel phase under the condition of low neodymium content, like the pure Ni–Zn ferrite. While neodymium oxide appears after the content of Nd3+ exceeds a certain limit (x > 0.04) and there exist two phases in the ferrite. The results of vibrating sample magnetometer (VSM) and vector network analyzer (VNA) show that adjusting the content of Nd is significant in improving the dielectric properties and microwave absorption capacity of the materials, specifically at low frequencies. When x < 0.04, the enhancement of dielectric loss ability of spinel ferrites by doping Nd3+ is the dominant factor affecting microwave absorption ability of samples. The secondary phase Nd2O3 hardly appears under this condition, thus the weakening effect of Nd3+ addition on magnetic loss ability is not obvious. When x = 0.04, the optimal absorption peak of the material reaches −20.8 dB at 4.4 GHz with a thickness of 8.5 mm and the effective absorption bandwidth (RL < −10 dB) was 3.2 GHz. On the contrary, when x > 0.04, the magnetic loss ability decreases rapidly (e.g., Ms decreases from 82.47 emu/g to 59.77 emu/g). Meanwhile, the dielectric loss increases slowly and the microwave absorption capacity decreases.

Effect of γ- rays irradiation on structural, electrical and magnetic properties of Dy3+ substituted nanocrystalline Ni-Zn ferrites

Nanocrystalline NixZn1-xDyyFe2-yO4 (x ≤ 0 ≤ 1.0; y = 0.0, 0.1) ferrites were prepared by solution combustion method. Structural investigation was studied using XRD, FTIR, SEM and EDAX techniques. All samples were irradiated with 60Co gamma source with total exposure dose of 310 kGy. XRD patterns revealed the formation of cubic spinel structure. FTIR spectra confirm the presence of two prominent vibrational bands. DC conductivity was found to obey the Arrhenius relation with a change in slope at Curie temperature and impedes with Dy3+ ion content. ZnFe2O4 nanoparticles exhibit a weak ferrimagnetic behavior at 300 K. The saturation magnetization, remanence magnetization, coercivity, remanence ratio, magneton number and Yaffet–Kittle angle were found to decrease in Dy3+ ion substituted samples attributed to redistribution of cations amongst the sites and weakening the A-B exchange interactions. The enhancement of DC conductivity and magnetic parameters on γ-irradiation attributed to surface states pinning of domains released.

Influence of cerium substitution on structural, magnetic and dielectric properties of nanocrystalline Ni–Zn ferrites synthesized by combustion method

Nickel–Zinc (Ni–Zn) ferrites substituted by cerium (Ce) and having the chemical composition Ni0.5Zn0.5Ce x Fe2−x O4 (x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were synthesized by combustion method using the organic fuel urea as reducing agent. The effects of cerium substitution on the structural, magnetic and dielectric properties of Ni–Zn compounds have been evaluated. X-ray diffraction patterns indicate that the Ni0.5Zn0.5Ce x Fe2−x O4 crystallizes into cubic spinel structure initially and secondary phase emerged along with main spinel phase when the Ce3+ content is increased. The elemental composition analysis confirms the stoichiometric presence of expected elements in the samples. Scanning electron microscope and high-resolution transmission electron microscope images reveal the nature of grain growth and the particle size of the synthesized samples. Fourier transform infrared spectroscopy confirms the formation of spinel phase and predicted the shifting of bands corresponding to Fe–O vibrations towards higher wavenumbers compared to undoped Ni–Zn ferrite. Magnetic characterization studies reveal that the substitution of Ce3+ into the Ni–Zn ferrite leads to a significant change in saturation magnetization and coercivity values. A plot of dielectric constant (ɛ′) versus applied electrical frequency measured at room temperature shows the normal dielectric behavior of the spinel ferrites. The introduction of Ce3+ rare earth ions into Ni–Zn ferrites samples is found to affect the values of both dielectric constant and AC conductivity.

Structural and Magnetic Studies of Cu-Substituted Nanocrystalline Ni–Zn Ferrites Obtained Via Hexamine–Nitrate Combustion Route

Ni ${}_{0.6 -_x}$ Cu x Zn0.4Fe2 O 4 ferrite compositions with x = 0.1, 0.2, 0.3, 0.5, and 0.6 were synthesized by a hexamine–nitrate combustion route. The phase purity and nanocrystalline nature was confirmed from XRD studies. The structural parameters such as lattice constant, X-ray density, bulk density, and porosity were calculated and compared for the effect of Cu inclusion in Ni–Zn ferrites. The lattice constant, X-ray density, and bulk density increase while the porosity exhibits a decreasing trend with increasing copper content. The FTIR spectra display two characteristic bands in the region 574–548 and 421–395 cm−1 assigned to M–O stretching vibrations in tetrahedral and octahedral sites, respectively. The AC susceptibility studies indicate the presence of superparamagnetic as well as single-domain particles and the decrease in Curie temperature with Cu substitution. The saturation magnetization, remanence, and coercivity were found to decrease with increasing Cu concentration and attributed to the lower magnetic moment of Cu ions than Ni ions.

Structural and magnetic properties of nanocrystalline Ni[sbnd]Zn ferrites: In the context of cationic distribution

Nanocrystalline NiZn ferrites (NixZn1-xFe2O4, x = 0.2–0.8) were synthesized by a novel and facile chemical method via a polymer precursor and their structural and magnetic properties were evaluated and discussed in correlation with the cationic distribution. The synthesis process involves a reaction of aqueous solutions of metal (Fe3+, Zn2+ and Ni2+) salts with an aqueous poly-vinyl alcohol (PVA)-sucrose solution at 60-65 °C. Controlled growth of the ferrite nanoparticles in terms of both composition and morphology was achieved by encapsulation of the nucleating sites in the PVA-sucrose polymer micelles. All the derived samples show single phase of cubic spinal structure (Fd3m space group). The microstructural features in the derived samples were evaluated with a field emission scanning electron microscope (FESEM) and a high resolution transmission electron microscope (HRTEM). Structural properties of the derived samples were studied with X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), Raman spectroscopy, energy dispersive X-ray (EDX) analysis, and Fourier transformed infra-red (FTIR) spectroscopy. Magnetic properties of the derived samples were studied with a vibrating sample magnetometer (VSM) at room temperature. The cationic distribution in the tetrahedral (A) and octahedral (B) sites of the mixed spinel structure was estimated from both XRD and EXAFS analyses. It was observed that Fe3+ ions migrate from the B to A-sites with the increase in Ni2+ concentration in the ferrite structure (NixZn1-xFe2O4, x = 0.2–0.8). The distribution of cations at the lattice sites has significant influence on the magnetic properties of the ferrite samples. The magnetization increases with the increase in Ni concentration in the samples till the maximum magnetization is observed in the composition Ni0.5Zn0.5Fe2O4. Further increase in Ni concentration reduces the magnetization. The results were explained on the basis of inter sub-lattice and intra sub-lattice coupling interactions between cations in A and B-sites.

Experimental characterization of nanocrystalline niobium-doped nickel–zinc ferrites: occurrence of superparamagnetism

Structural, morphological, magnetic, and dielectric investigations are carried out in Nb-doped (viz., for x equal to 0.0–0.4 by wt%) nanocrystalline Ni–Zn ferrites synthesized by hydrothermal method. XRD, IR studies infer the growth of nano structures and Fe2O3 phase. Nb ions segregate at grain boundaries. Crystallite size (D) varies from 62 to 18 nm with x. FTIR absorption exhibits split at higher x. Saturation magnetization witnesses an overall decrease with x. Trends of Ms(x) are explained by nature of dopant, preferential replacement, surface canting (Y–K angles) and lattice contraction. Variations of coercive field (Hc) and D infer single-domain to multi-domain morphological transformation. Occurrence of superparamagnetism (SPM) is predicted for zeroed values of Hcand for a critical concentration xcrit equal to 0.321. Enhanced Nb5+–Fe2+ binding with dopant (x up to 0.2) results for decrease in dielectric constant \( \varepsilon^{\prime}_{r} \), loss factor tanδ and increase in resistivity ρ. Lowered ac conductivity is attributed to blockade of path by Nb5+ ions in the vicinity of B-sites. Relatively higher ρ (~108 Ω cm) and lower loss (tanδ ~10−2–10−3) evinced for 10 kHz. Enhanced core loss is realized with x manifested as lowered Hc and tanδ to usher their utility in high-frequency applications.

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

Nano crystalline Ni–Zn ferrites of composition Ni0.5Zn0.5Fe2O4have 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 89.50emu/g as a function of sintering temperature making this material useful for high frequency applications. Electromagnetic studies showed sustained values of permittivity up to 1GHz. These results have been explained on the basis of various models and theories.

Study of structure and magnetic properties of Ni–Zn ferrite nano-particles synthesized via co-precipitation and reverse micro-emulsion technique

Nano-crystalline Ni–Zn ferrites were synthesized by chemical co-precipitation and reverse micro-emulsion technique with an average crystallite size of 11 and 6 nm, respectively. The reverse micro-emulsion method has been found to be more appropriate for nano-ferrite synthesis as the produced particles are monodisperse and highly crystalline. Zero-field cooled and field cooled magnetization study under different magnetic fields and magnetic hysteresis loops at different temperatures have been performed. The non-saturated M–H loops, absence of hysteresis, and coercivity at room temperature are indicative of the presence of super paramagnetic and single-domain nano-particles for both the materials. In sample ‘a’, the blocking temperature (TB) has been observed to decrease from 255 to 120 K on increasing the magnetic field from 50 to 1,000 Oe, which can be attributed to the reduction of magneto crystalline anisotropy constant. The MS and coercivity were found to be higher for sample ‘a’ as compared with sample ‘b’ since surface effects are neglected on increasing the crystallite size.

Magnetic properties and cation distribution study of nanocrystalline Ni–Zn ferrites

Nanocrystalline spinel ferrites with general formula Ni1−xZnxFe2O4 (x=0−1.0) were prepared by an oxalate co-precipitation method. Magnetic properties were investigated by means of saturation magnetization, AC susceptibility, cation distribution and Curie temperature measurements. The saturation magnetization increases with increasing concentration of zinc up to x=0.4 and then decreases with increasing zinc concentration. Investigation of the Yafet–Kittel (Y–K) angles shows the existence of Neel’s two sublattice model for x≤0.2 and Y–K model for x≥0.4 compositions. Variation of normalized AC susceptibility with temperature shows single domain particle nature for the compositions x≤0.2, whereas multi-domain particle nature for the compositions x≥0.4. Curie temperatures of the samples decrease with the increase in zinc concentration. Upadhayay’s model is used to investigate the cation distribution and hence to calculate the Curie temperature. The composition for x=1 shows paramagnetic behavior at and above room temperature.

Dielectric Behaviour of Nanocrystalline Ni-Zn Ferrites Prepared by Oxalate Co-Precipitation Method

Nickel–zinc ferrites with chemical formula Ni1-xZnxFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) were prepared by oxalate co-precipitation method. The dielectric constant (ε') dielectric loss (tanδ) and AC conductivity (σac) of all the samples were determined at room temperature in the frequency range 20Hz -1MHz. The dielectric constant and dielectric loss are much smaller than those for samples prepared by ceramic method. The dielectric behaviour is attributed to the Maxwell–Wagner type interfacial polarization. AC conductivity of all the samples lies in the range 1.20×10-8 to 54.7×10-8 Ω-1cm-1. Low dielectric loss and high resistivity suggest the suitability of these ferrites for high frequency applications.

Fabrication of Cu2+ substituted nanocrystalline Ni–Zn ferrite by solution combustion route: Investigations on structure, cation occupancy and magnetic behavior

The reactivity of Cu2+ ion concentration in Ni–Zn spinel matrix fabricated using solution combustion route has been investigated. The specimens of nanocrystalline Ni0.8−xCuxZn0.2Fe2O4 (x=0.0⩽0.6 with steps of 0.2) exhibits single phase cubic structure. The detailed studies regarding the physico-chemical stability, crystal structural stability, surface morphology and magnetic properties as a function of Cu2+ ion concentration were performed. The annealing treatment does not alter the crystal structure but increases the crystallinity of the samples. The cation occupancies of the prepared materials were estimated by using X-ray diffraction (XRD) data analysis. The morphological investigations of the samples were studied by using field emission scanning electron microscopy (FE-SEM) technique. The crystallographic analyses of all the compositions were systematically investigated by Fourier transform infrared spectroscopy (FTIR). The saturation magnetization (M–H plots) at room temperature with field 10kOe exhibits strong influence of Cu2+ ion content and annealing temperature.

Double-layer microwave absorber based on nanocrystalline Zn0.5Ni0.5Fe2O4/α-Fe microfibers

The microwave absorption properties of the nanocrystalline NiZn ferrite (Zn0.5Ni0.5Fe2O4) and iron (α-Fe) microfibers with single-layer and double-layer structures were investigated in the frequency range of 2–18GHz. The double-layer absorbers have much better microwave absorption properties than the single-layer absorbers, and the microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the absorbing layer and matching layer. With the absorbing layer thickness 0.7mm of α-Fe microfibers–wax composite and the matching layer thickness 1.5mm of Zn0.5Ni0.5Fe2O4 microfibers–wax composite, the minimum reflection loss (RL) reaches about −71dB at 16.2GHz and the absorption band width is about 9.2GHz ranging from 8.8 to 18GHz with the RL value exceeding −10dB. While, when the absorbing layer is the Zn0.5Ni0.5Fe2O4 microfibers–wax composite with thickness 1.8mm and the matching layer is the α-Fe microfibers–wax composite with thickness 0.2mm, the RL value achieves the minimum about −73dB at 13.8GHz and the absorption band width is about 10.2GHz ranging from 7.8 to 18GHz with the RL value exceeding −10dB, which covers the whole X-band (8.2–12.4GHz) and Ku-band (12.4–18GHz).

Synthesis of nanocrystalline Ni–Zn ferrites by combustion method with no postannealing route

Nanocrystalline Ni–Zn ferrites were synthesized by a novel combustion route without post annealing process. The sintered ferrites characterized by X-ray diffraction have shown highly pure nanocrystalline phase. Calculated by the Scherrer’s formula, the estimated crystallite size is about 26–41 nm and lattice constant of the cubic spinel was 8.353–8.458 Å. The saturated magnetization is in the range of 6–57 emu/g and the corresponded coercivity varies from 26 to 221 Oe. Further, the high frequency electromagnetic properties were investigated by analysis of magnetoimpedance spectra. The novel combustion synthesis without post annealing has implied for practical industrial fabrication of ferrites for electromagnetic applications, inherently interest of energy efficiency and cost effective.

Mechanosynthesis of nanostructured magnetic Ni–Zn ferrite

Nanocrystalline Ni–Zn ferrite (NiZnFe 2O 4) was directly produced by high energy ball milling of stoichiometric mixture of ZnO, NiO, Fe 2O 3 powders. X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), simultaneous thermal analysing (STA), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM) were carried out to characterize the structural, chemical and magnetic aspects of NiZnFe 2O 4 compound. The formation of NiZnFe 2O 4 phase appeared to involve two stages; development of Zn ferrite by diffusion of ZnO in Fe 2O 3 followed by diffusion of NiO in Zn ferrite to form Ni–Zn ferrite. The crystallite size of final product after 60 h of ball milling time was estimated to be 18 nm which increased to 45 nm after annealing at 800 °C for 4 h. After annealing of ball milled powders, the saturation magnetization was increased and coercivity was decreased as lattice defects and internal strain reduced.

Synthesis, Microstructure and Magnetic Properties of Nanocrystalline Ni-Zn Ferrite by a Modified Wet Chemical Method

Nanocrystalline Ni1-xZnxFe2O4 ferrites with 0 ≤ x ≤ 1 were prepared by sprayingcoprecipitation method. The microstructure was investigated by TG-DSC, XRD, SEM, TEM and BET. Magnetic properties were measured with vibrating sample magnetometer at room temperature. The results showed that uniform and fine nanocrystalline Ni1-xZnxFe2O4 ferrites are obtained. The grain size of sample calcined at 600°C for 1.5h is about 30nm. There are a few agglomerates with average sizes below 100nm. The specific saturation magnetization, Ms, of the sample increases with increasing Zn2+ concent x at room temperature, and the maximum Ms is 66.8 A·m2·kg-1 as the Zn2+ content x is around 0.5mol. As calcining temperature increased from 400°C to 1050°C, the Ms of Ni0.5Zn0.5Fe2O4 ferrite increases from 40.2 A·m2·kg-1 to 75.6 A·m2·kg-1. The coercivity maximum is about 5.97 kA·m-1 as its critical grain size is about 62.0nm. The relation between coercivity and grain size for nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite may be explained based on random anisotropy theory.

Grain size effect on the dielectric behavior of nanostructured Ni0.5Zn0.5Fe2O4

The dielectric properties of nanocrystalline Ni0.5Zn0.5Fe2O4 spinel ferrite with various grain sizes, obtained by mechanically milling, have been studied using impedance measurements in the frequency range from 1 Hz to 10 MHz and in the temperature range from 300 to 823 K. The effect of milling, frequency, and temperature on the dielectric properties of nanocrystalline Ni-Zn ferrite is discussed. The real part of dielectric constant (ε′) for the 14 nm grain size sample is found to be about an order of magnitude smaller than that of the bulk nickel zinc ferrite. The anomalous frequency dependence of ε′ has been explained on the basis of hopping of both electrons and holes. The unusual increase in dielectric loss with milling is because of the increase in electrical conductivity due to oxygen vacancies introduced upon milling. The electrical modulus has been fitted to a stretched exponential function and the results clearly reveal the presence of the non-Debye type of dielectric relaxation in this material. The relaxation frequency is observed to decrease with milling due to increasing interaction between charge carriers arising out of oxygen vacancies introduced by milling. The mechanism for the electrical conduction is found to be the same as that for the dielectric polarization.