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Ni0.5Zn0.5Fe2O4 powders were prepared by a novel molten‐salt synthesis method. The effects of calcination processes of the powders on their sintering behaviors were investigated. Compared with the synthesis by traditional solid‐state reaction, the proposed molten‐salt method can significantly reduce the synthesis temperature of Ni0.5Zn0.5Fe2O4 from 800 to 550°C below, and the prepared powders have relatively high sintering activity at low temperature, which can thus decrease the sintering temperature. However, the abnormal growth of grains is easy to occur during sintering, thus resulting in uneven grain size. In particular, during the molten‐salt synthesis, the holding time for calcination is a dominant factor affecting the activity and crystallization degree of the resultant powders. From the point of view of increasing the density of sintered bodies, the optimal conditions for synthesizing Ni0.5Zn0.5Fe2O4 powder by the proposed molten‐salt synthesis is 400°C for 6 h. In addition, the saturate magnetization of the finally obtained ferrite ceramics has nothing to do with the preparation processes, while their coercivity depends on their densification and grain size caused by their different processing routes. [ABSTRACT FROM AUTHOR]

A series of diamagnetic aluminum (Al3+) substituted Ni-Zn Nanoferrites have been synthesized using sol-gel auto combustion route. Structural, magnetic, and dielectric properties were systematically studied and reported with respect to Al3+ substitution in host Fe3+ ions. X-ray diffraction (XRD) and infrared spectroscopy (IR) measurements confirm the presence of Al3+ ions at both A and B sites. Cation distribution proposed from XRD and IR correlates with magnetic and dielectric results. It is observed that Al3+ ions are distributed in to tetrahedral and octahedral sub-lattices. The saturation magnetization varies between 58.5 and 44.2 emu/g with increasing Al3+ substitution. This decrease in magnetization is ascribed to presence of the non-collinear spin (canted spin) structure in octahedral sub-lattice. Dielectric constant decreased and a significant improvement in AC resistivity is observed with Al3+ substitution. The observed variations are accounted on the basis of cation distribution in spinel ferrite. [ABSTRACT FROM AUTHOR]

Ni-Zn ferrite nanoparticles were synthesized via mechanical activation of Zn, NiO and Fe 2 O 3 powders in a high energy planetary ball mill. The 30 h-milled samples in argon, oxygen and air atmospheres were pressed in pellet and toroid shape form and were sintered from 500 °C to 900 °C with 100 °C increments. The X-ray diffraction patterns results indicated a single phase Ni-Zn ferrite formation with a cubic-spinel structure in all the samples sintered at 500 °C. The milling atmosphere had a key role in the synthesis, microstructure and properties of the samples in such a way that this effect sustained even after the completion of sintering process. Thus, the main goal of this study is to scrutinize the effect of sintering temperature in the 30-h-milled samples in different atmospheres on DC electrical resistivity and dielectric behavior of Ni-Zn ferrite samples. The results indicated that although electrical resistivity decreased, dielectric behaviors, i.e. constant, loss and tan δ increased with increase in sintering temperature. The milled samples in argon had the highest resistivity of 1.2 × 10 6 Ωcm at 500 °C, and lowest dielectric constant and loss ( ∼ 4.67 × 10 2 and 1.7 at 300 K and frequency 10 6 MHz, respectively) compared to other samples owing to more homogeneity and smaller average crystallite size, making them a good candidate for high frequency applications. X-ray photoelectron spectroscopy (XPS) revealed the presence of metal ions in their proper valence in the Ni-Zn ferrite crystal structure. Noticeably, a variation in the binding energy for the milled samples in different atmospheres is attributed to the changes in surroundings of Fe 3+ and Zn 2+ /or Ni 2+ , due to non-equilibrium distribution of cations in tetrahedral and octahedral sites, which is further confirmed by the XRD patterns. [ABSTRACT FROM AUTHOR]

The Sn-substituted Ni-Zn ferrites, (0.0≤ x ≤0.30), have been synthesized by the standard double sintering technique from the oxide nanopowders of Ni, Zn, Fe and Sn. The structural and electrical properties have been investigated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), DC resistivity and dielectric measurements. From XRD data, the single cubic spinel phase has been confirmed for x ≤0.1, whereas for x >0.1 an extra intermediate phase has been detected along with the cubic spinel phase of Ni-Zn ferrite. The grain size is increased due to Sn substitution in Ni-Zn ferrites. DC resistivity as a function of temperature has been measured by two probe method. The semiconducting nature has been found operative in the samples. The DC resistivity was found to decrease whilst the dielectric constant increased with increasing Sn content in Ni-Zn ferrites. The unusual behavior of the dielectric loss factor of the ferrites was explained by the Rezlescu model. The electrical relaxation of the ferrites has been studied in terms of electric modulus formalism and the time for dielectric relaxation was calculated. The contribution of grain resistance has been studied from the Cole-Cole plot. The suitability to use the as prepared samples in the miniaturized memory devices based capacitive components or energy storage principles are confirmed from the values of dielectric constant. [ABSTRACT FROM AUTHOR]

Ni-Zn ferrites of nominal composition Ni 0.5 Zn 0.5 Sm x Fe 2- x O 4 ( x =0–0.1) were prepared by a conventional two-steps solid sintering method. The effect of Sm 3+ doping on the microstructural, magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. The main phase of all the samples was ferrite spinel, and the samples doped with Sm 3+ ions contained a small amount of a foreign SmFeO 3 phase as well. And the doping of Sm 3+ resulted in the increase of lattice constant. The grain size, density and densification of the ferrites initially decreased after Sm 3+ doping, but then increased with more Sm 3+ doped. With increasing substitution level, x , the saturation magnetization of the as-prepared ferrites decreased, while the coercivity increased. The Curie temperature raised initially and decreased later with increasing content of Sm 3+ in the samples, reaching a maximum of 274 °C when x =0.025. The initial permeability of the ferrites first decreased and then increased with increasing doping amount of Sm 3+ ions. The introduction of Sm 3+ ions into Ni-Zn ferrite would lead to the reduced dielectric loss in the frequency range of 1–100 MHz, but the dielectric loss raised when more Sm 3+ was added in the frequency range of 100–1000 MHz. When x =0.05, the dielectric loss reached the lowest value. [ABSTRACT FROM AUTHOR]

The constant heating rate method employed in sintering studies offers several advantages over the isothermal method, particularly the fact that all the parameters that describe the sintering phenomena can be obtained from a single sample. The purpose of this work is to determine the parameters of sintering kinetics of nanosized Ni-Zn ferrite powders synthesized by combustion reaction. The nonisothermal sintering method was studied using a constant heating rate (CHR). The Ni-Zn ferrite powders, with average particle size varying from 18 nm to 29 nm, were uniaxially pressed and sintered in an horizontal dilatometer at a constant heating rate of 5.0 °C/min from 600 °C up to complete densification, which was reached at 1200 °C. The compacts were characterized by scanning electron microscopy (SEM). Experimental results revealed three different sintering stages, which were identified through the Bannister Theory. The shrinkage and the shrinkage rate analyzed showed a viscous contribution in the initial sintering stage, which was attributed to the mechanism of structural nanoparticle rearrangement.

Polycrystalline nickel-zinc ferrites of chemical formula Ni0.65-xMgxZn0.35Fe2 O4 (x = 0.00 to 0.2 in steps of 0.04) have been prepared by conventional ceramic technique. Calcination and sintering of all samples have been carried out in air atmosphere at 950°C and 1250°C, respectively, followed by natural cooling to room temperature. All the samples were characterized by the X-ray diffraction (XRD) for structure determination. These samples were then investigated for their magnetic and electric properties, including saturation magnetization, Curie temperature, initial permeability measurements and DC electrical resistivity. Porosity was decreased drastically from 15% to 5% showed better quality of the sintered samples. There were increments in initial permeability and DC electrical resistivity throughout the series of samples. Variations in the observed properties as a function of magnesium concentration have been discussed in light of the existing understanding. [ABSTRACT FROM AUTHOR]

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Abstract: Ni–Zn ferrite, Ni0.3Zn0.7Fe2O4, with a wide variation of grain sizes has been prepared via high energy ball milling through two different sintering routes: multi-sample sintering and single-sample sintering. The parallel relationships between evolving microstructural properties and AC magnetic response parameters were investigated using a FEI Nova NanoSEM 50 series and an Agilent Model HP4291B Impedance/Material Analyzer respectively. SEM micrographs showed larger grain size as the sintering temperature increased, consequently increasing the number of multi-domain grains. The AC magnetic response parameters belong to three groups with strongly, moderately and weakly ferromagnetic behavior respectively. Single-sample sintering and multi-sample sintering evolution yield quite similar permeability-grain size relationship trends. The permeability from both sintering routes is influenced by several factors which are degree of crystallinity, dominant magnetization process (ease of domain walls movement in multi-domain grains or spin rotation in single-domain grains) and large enough grain size which surpasses the critical grain size for transition from single-domain to multi-domain grains. [Copyright &y& Elsevier]

Being materials with a large number of interesting properties, ferroelectric-ferrite based composites have recently been developed. People are showing a great interest in these materials due to some unique properties like magnetoelectric effect in addition to the ferroelectric, dielectric and magnetic properties. After a review of literature it is found that the variation in different properties of PZT ceramics is found to depend on the amount of ferrite content. In this paper, we are reporting the variation in ferroelectric properties of PbZr0.65Ti0.35O3 (PZT) by varying Ni-Zn ferrite (NZF) content. The studied system having compositional formula (1-x) PZT-x NZF (0 ≤ x ≤ 0.025, in steps of 0.005), was prepared by solid state route using microwave sintering. Remanant polarization was found to be monotonically decreasing with increasing ferrite content as observed from the recorded P-E hysteresis loops for all the samples at 20 Hz. Microwave sintering results in significant improvements in properties as compared to conventionally sintered samples. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline Ni–Zn ferrite samples with different microstructures have been prepared by the conventional ceramic technique, and their complex permeability and permittivity spectra have been studied. The permeability spectra have been resolved into contributions of domain wall resonance and spin rotation relaxation. The fitting results of permeability dispersion have revealed the relationships between domain wall resonance, spin rotation relaxation mechanisms, and microstructures. With increasing average grain size, the permittivity also gradually increased. However, extremely big grain size led to an uneven permittivity–frequency curve. These results may be rationalized in terms of the modifications of the microstructures brought about by the different sintering temperatures. [Copyright &y& Elsevier]

Abstract: The as-prepared Ni0.5Zn0.5Fe2O4 powders fabricated directly from the solution of metal nitrates by the refluxing method were testified by the analysis of XRD, TEM, SAED and HRTEM. XRD pattern indicated that obtained Ni0.5Zn0.5Fe2O4 powders were single phase with spinel structure, TEM analysis showed that the powders with cubic shape were uniform in particle size of about 10–20 nm. Ceramics prepared by the as-synthesized Ni0.5Zn0.5Fe2O4 powders sintered at various temperatures between 950 °C and 1150 °C for 2 h were observed by SEM technique, which indicated that the Ni0.5Zn0.5Fe2O4 ferrites can almost be sintered to theoretic density at 1100 °C for 2 h, lower by at least about 200 °C compared with those ferrites prepared by the conventional oxide method. The relative magnetic loss tanδ/μ i of the ceramic samples sintered at the temperature 1050 °C was measured to be of the order of 10−4–10−5 in the frequency range from 1 MHz to 10 MHz, and the threshold frequency of the ferrites was 77.2 MHz. [Copyright &y& Elsevier]