Preeti Mathur

Processing of High Density Manganese Zinc Nanoferrites by Co-Precipitation Method

Nanoparticles of spinel ferrites MnxZn1-xFe2O4 with x = 0.0 to 1.0 were prepared by co-precipitation method. The ferrite samples were pre-sintered at 200°C at the rate of 200°C/h for 15h. Finally, one set of samples was sintered at 400°C and the other set at 500°C at the rate of 200°C/h for another 15h. The spinel structure was confirmed by X-ray diffraction (XRD) pattern. The particle size was calculated by using Debye–Scherrers equation for Lorentzian peak. The calculated average particle size lies between 19–53 nm. The particle size was also investigated by using scanning electron microscopy (SEM). Both the results were found to be in good agreement. The resistivity data was taken by two probe method and resistivity, activation energy and porosity were calculated. There was an increase in the resistivity and activation energy when the ferrite samples were sintered at a higher temperature. Possible models, theories and mechanisms contributing to these processes have been discussed.

Preparation and Characterization of Mn0.4NixZn0.6−xFe2O4 Soft Spinel Ferrites for Low and High Frequency Applications by Citrate Precursor Method

In the present study, preparation and characterization of Mn-Ni-Zn soft ferrites with chemical formula Mn0.4NixZn0.6−xFe2O4, where x = 0.0, 0.2 and 0.4, by citrate precursor method has been reported. Microstructural properties studied with the help of X-ray diffraction and scanning electron microscopy show that the samples have almost uniform sized crystallites and have single phase spinel structure. The properties like initial permeability, permeability loss, dielectric constant, dielectric loss are studied as a function of frequency. The d.c. resistivity of the samples is also studied. Variation of d.c. resistivity with composition, x, of the ferrite sample shows that pure zinc ferrite has more resistivity than that of nickel substituted zinc ferrite. The dispersion in the magnetic and electrical properties has been discussed by using various mechanisms, models and theories.

Controlling the Properties of Manganese-Zinc Ferrites by Substituting In3+and Al3+Ions

The effect of substitution of In3+ and Al3+ ions on the electrical and magnetic properties of Mn-Zn ferrites has been investigated. The substitution of In3+ ions for Fe3+ ions resulted in an increase of lattice parameter, owing to the larger size of In3+ ions, whereas lattice parameter was found to decrease on substituting Al3+ ions in place of the Fe3+ ions, owing to the smaller size of Al3+ ions. The dc resistivity was found to increase with the substitution of In3+ and Al3+ ions in the Mn-Zn ferrite system. The improvement in the dc resistivity has been observed at the expense of deterioration in the magnetic properties of Al3+ substituted Mn-Zn ferrites. A significant reduction in the values of initial permeability, saturation magnetization and Curie temperature was observed with successive increase of Al3+ ions. The saturation magnetization and initial permeability were found to increase with incorporation of In3+ ions. A marked increase in the value of initial permeability was found for the Mn0.4Zn0.6In0.5Fe1.5O4 ferrite. Curie temperature was found to decrease with an increase of In3+ ion concentration. These changes in the properties are explained on the basis of their magnetic interactions, a modified cation distribution and various models.

IMPACT OF PROCESSING AND POLARIZATION ON DIELECTRIC BEHAVIOR OF NixMn0.4-xZn0.6Fe2O4 SPINEL FERRITES

In this paper, dielectric properties of NixMn0.4-xZn0.6Fe2O4 ferrites with x varying from 0.05 to 0.35 prepared by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. A decrease in the dielectric constant is observed with the increase in Ni concentration except for x = 0.3. This decrease in dielectric constant with the increase in Ni concentration is justified by inverse proportionality between resistivity and dielectric constant. Dispersion in the dielectric constant with frequency in the range of 75 Hz to 30 MHz is observed. Resonance peaks were observed in tan δe versus frequency curve for all the samples. A shift in the resonance frequency toward higher frequency is observed with the increase in temperature. The peak height also increases with an increase in temperature. Phase change is confirmed by differential scanning calorimetry. Structural studies have been done by X-ray diffraction technique and scanning electron microscopy. Possible theories, models, and mechanisms contributing to these processes have been discussed.

A study of nano-structured Zn?Mn soft spinel ferrites by the citrate precursor method

In the present study, the ZnxMn1 - xFe2O4 series of ferrites, where x= 0.1, 0.3, 0.5, 0.7 and 0.9, are prepared by the citrate precursor technique. One set of samples is subjected to the normal pressing technique and the other to the hot-pressing technique. X-ray diffraction (XRD) and scanning electron microscopy techniques are used to study the structural properties of the given series of ferrites. The results are found to be in good agreement. Hot pressing of Zn?Mn ferrites results in improvement of their magnetic and micro-structural properties as it controls simultaneously grain growth and porosity. However, hot pressing of Zn?Mn ferrites results in deterioration of their dc resistivity. The cation distribution has been studied by using x-ray analysis and magnetization. The variation of saturation magnetization and Curie temperature with increasing concentration of Zn2+ ions can be explained on the basis of cation distribution and Neels two-sublattice models. M?ssbauer studies were carried out to confirm the superparamagnetic behaviour of the nanoferrites. The possible mechanisms, models and theories contributing to these results have been discussed.

Effect of particle size on the properties of Mn-Zn-In ferrites

In the present study, we have synthesized Mn0.4Zn0.6In0.5Fe1.5O4 ferrites by the normal ceramic method and the citrate precursor method. The structural studies have been made by using an x-ray diffraction (XRD) technique and scanning electron microscopy (SEM), which confirmed the formation of a single-phase spinel structure. In the normal ceramic methods, we cannot control the particle size and porosity, whereas in precursor methods, we can control both. Using the citrate precursor method, we have simultaneously reduced the particle size and sintering temperature as compared to the normal ceramic method. There is an increase in dc resistivity, reduction in dielectric constant, electrical and magnetic losses by the citrate precursor method as compared to the normal ceramic method. The initial permeability is also reduced using the citrate precursor method as compared to the normal ceramic method. However, with sintering temperature, the initial permeability increases. These observations are explained on the basis of various models and mechanisms.

COMPARATIVE STUDY OF DIELECTRIC BEHAVIOR OF Mn0.4Zn0.6Fe2O4 NANOFERRITE BY CITRATE PRECURSOR METHOD

In the present work, comparative study of the dielectric behavior of Mn0.4Zn0.6Fe2O4 ferrite synthesized with and without H2O2 (hydrogen peroxide) has been presented. The dc resistivity has been improved by the citrate precursor method as compared to the ceramic method, and it is further improved by the addition of H2O2, which acts as a strong oxidizing agent. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanocrystallites and the average size of these nanocrystallites–calculated by Scherrers formula–depends on the polarizer. The average particle size was found to be ~70 nm with H2O2 and ~88 nm without H2O2. The particle size is further confirmed by scanning electron microscopy. Both the results are found to be in good agreement. The decrease in dielectric constant and dielectric loss factor by addition of oxidizing agent is justified by inverse proportionality between the resistivity and dielectric constant. Possible mechanisms contributing to these processes have been discussed.

PROCESSING OF NANO-CRYSTALLITE SPINEL FERRITE PREPARED BY CO-PRECIPITATION METHOD

Mn0.4Cu0.4Zn0.2Fe ferrite was synthesized by soft chemical approach called co-precipitation technique. The ferrite powder was calcined, compacted and sintered at 700°C and 800°C for 3 h. The initial permeability, density, grain size, Curie temperature and dc resistivity have been studied. X-ray diffraction (XRD) method confirmed the sample to be a single-phase spinel structure without unreacted constituents. The particle size was calculated from XRD spectrum using Scherrers formula and found to be ~55 nm. Then, nanoparticles were observed with tunneling electron microscopy (TEM). Further, scanning electron micrograph (SEM) also confirmed nano-phase and the uniformity of the particles. The initial permeability values do not exhibit much variation with temperature, except near Curie temperature, where it falls sharply. The initial permeability is found to increase with the increase in sintering temperature. This is attributed to the increase in the grain size. Calculation of activation energy indicates that the given ferrite is p-type semiconductor. Mossbauer study of these samples shows superparamagnetic behavior, which also confirms the formation of nano-particles. Possible models and mechanisms contributing to these processes have been discussed.