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Copper substituted Ni–Zn ferrite powders of Ni0.8−xCuxZn0.2Fe2O4 with 0 ≤ x ≤ 0.4 composition are synthesised at 80°C by soft chemical route. Their electrical, magnetic, and microstructural properties are studied using XRD, VSM and SEM techniques. These studies revealed that the bulk density, dc electrical resistivity and initial permeability increased considerably with the optimum copper concentration of x = 0.2. The major achievement was the decrease in its loss factor in the MHz frequency region. The improvement in the electrical and magnetic properties was attributed to the uniform grain-growth/microstructure of the copper substituted ferrite achieved at a lower sintering temperature T ≈ 1000°C.

Polycrystalline nickel-zinc ferrite powder was obtained by chemical coprecipitation involving the corresponding metal nitrates and sodium hydroxide. The precipitate, when dried at 80 °C in air, was characterized by powder XRD, SEM and VSM measurements. It shows the formation of cubic ferrite with saturation magnetization M s ≈ 44 emu / g . When calcined at 1200 °C, the magnetization reached 96% of the saturation value, M s ≈ 67 emu / g . The temperature dependence of magnetization confirmed the Curie temperature T c ≈ 480 ° C.

A novel chemical passivation route is established to obtain microcrystalline solid solutions of binary oxide system Mn1−x Ni x O (0·01

A novel method of preparation, involving careful formation of a stoichiometric solid solution of stabilized Mn1-x Mg x O system for eight different concentrations ofx (0.001 ⩽x ⩽ 0.15) is described. A variety of physicochemical techniques such as X-ray diffraction, DTA-TGA, reflectance spectra, magnetic susceptibility and XPS data are used to determine structure-property correlations in the solid solutions, which are (i) X-ray diffraction studies reveal the linear decrease of cubic lattice parameter with increasing x, (ii) DTA-TG-DTG studies which confirm the formation of solid solution and the stability of these solid solutions in air which increases from 515 to 565 K withx, (iii) the diffused reflectance spectra shows nearly perfect octahedral symmetry around Mn2+ ions, (iv) magnetic susceptibility data indicates the usual dilution effects of diamagnetic ions in antiferromagnetic host lattice, (v) XPS studies reveal the presence of mixed phase of Mn2O3-MgO on the surface which protects the bulk MnO from its further oxidation to higher oxides of manganese. This shows the important role of Mg2+ in the chemical passivation of manganous oxide.

Active powders of Ni–Zn ferrite were synthesized by soft chemical approaches and were processed with varying concentrations of Bi2O3. The sintered products were characterized extensively using a vibrating sample magnetometer, scanning electron microscopy, and resistivity techniques. The loss factor and the permeability have been evaluated. At an optimum concentration of Bi2O3 doping the loss factor has been reduced by 20%. The rotational responses are found to be strongly dependent on particle size.

Active powders of Ni–Zn ferrite were synthesized by soft chemical approaches and were extensively characterized using x-ray diffraction, scanning electron micrographs, vibrating sample magnetometer, resistivity, and permeability/loss factor techniques. The variation in the sintering conditions established a useful microstructure–magnetic permeability correlation.

Active powders of Ni–Zn ferrite were synthesized by soft chemical approaches and were processed with varying concentrations of Bi2O3. The sintered products were characterized extensively using a vibrating sample magnetometer, scanning electron microscopy, and resistivity techniques. The loss factor and the permeability have been evaluated. At an optimum concentration of Bi2O3 doping the loss factor has been reduced by 20%. The rotational responses are found to be strongly dependent on particle size.

Magnetic susceptibility studies of Mn1-xMxO (M = Zn, x≤0.1; M = Mg, x≤0.12;M = Fe, x≤0.4) in the range 77 to 300 K are reported. The methods of preparation of Mn1-xMxO systems preclude the presence of trivalent ions. The M1-xFexO system shows anomalous behaviour aroundx = 0.2–0.3. The results are discussed in terms of competition between the nearest neighbour and the next-near-neighbour interactions, dilution effects and cooperative effects of FeO6 octahedra.

Easily oxidizable oxides, FeO, and MnO, are unstable in air but can be easily stabilized by small amounts of other oxides. Further these two unstable oxides stabilize each other very well. Such stabilized FeO and MnO provide easy and reproducible methods of preparing electronic ceramics that need such unstable valency states in them. Ferrous-zinc ferrite has been successfully synthesized employing FeO stabilized with a small amount of Fe3O2.

Thermal (DTA/DTG/TG) studies have been carried out in order to understand the ferritization reaction leading to the formation of hexagonal strontium ferrite. Two different routes, namely, (a) the conventional ceramic method (solid state reaction) and (b) the chemical coprecipitation method, have been used to prepare the starting materials. Simultaneous DTA/DTG/TG plots clearly exhibit the onset of the exothermic ferritization reaction at T ⋍ 730°C, with an activation energy of 43.872 kcal mol −1 for the precursors derived from the coprecipitation route. On the other hand, the temperature required for the reaction with the ceramic route precursors was greater than 900°C without any accompanying energy change.

Highly uniform submicrometre size particles of hexagonal strontium ferrite (SrFe12O19) have been synthesized by chemical coprecipitation technique at pH ⋍ 13. Chemical coprecipitation technique has helped in bringing down the ferritization temperature from 1300 to 925° C which is revealed by DTA-TG and XRD studies. Reproducible uniform single domain particle size and its distribution has been observed by scanning electron microscopy. X-ray and Mossbauer studies have identified single phase ferrite with Fe3+ ions occupying the proper crystallographic sites. The performance parameters of the sintered isotropic strontium ferrite magnets have proved to be superior by about 20% over the ferrites prepared by conventional ceramic technique.

Manganous-zinc ferrites are best prepared directly from MnO and can be conveniently pressed with non-volatilizable binders such as polyvinyl alcohol which however can be burnt out without oxidizing the Mn2+ in the ferrite by sintering in a static atmosphere generated by the thermal dissociation of active ferric oxide pellets placed out of contact with the ferrite in the closed sintering unit. Such a process eliminates cracks and rejections in the sintered pieces besides giving very satisfactory and reproducible results.

Highly unstable FeO is chemically passivated by incorporating Cr3+ ions by solid solution technique and forming FexO∶Cr3+ single phase material. XRD, chemical analysis and Mossbauer spectroscopy are used for the characterization of the freshly prepared as well as samples aged in the desiccator for nearly three months. Optimum concentration range — 0.25 to 0.75 mole% — of Cr2O3 has been found to be necessary for stabilizing FexO∶Cr3+. x is determined by chemical analysis. Mossbauer and XRD studies have confirmed the chemical passivation of unstable FeO.

Active manganous oxide preparedin situ is mixed in a closed system with a coprecipitated mixture of zinc and ferric oxides, and then heated in an inert atmosphere to 800°C to form the manganous zinc ferrite at this relatively low temperature. A volatilizable binder employed for pressing is first distilled off in an inert atmosphere and the sintering is then carried out in a controlled static atmosphere. The formation of the spinel with total absence of Mn3+ far below the sintering temperature, and the subsequent sintering without any possibility of oxidation of Mn2+ at any stage result in improved properties.

Stoichiometric polycrystalline samples of Mn x Mg 1− x Fe 2 O 4 (0·5 ≤ x ≤ 0·66) have been synthesized by following a novel route using stabilized MnO and Fe 2 O 3 at high temperatures. This route precludes the formation of large amounts of Mn 3+ and Fe 2+ and precipitation of MgO and α-Fe 2 O 3 which are generally observed during the usual route of preparation by conventional ceramic techniques. These samples have been characterized for their structural and magnetic properties using X-ray diffraction, Fe 57 Mossbauer spectroscopy and bulk magnetic properties such as initial permeability, loss factor, ferromagnetic transition temperature, remanance and coercivity. For X = 0·62, these ferrites exhibit the highest remanance ratio ≅0·96, suitable for square loop applications.

Ferrous-zine ferrites, ZnxFe3−xO4(0

Mesures de conductivite electrique et de force thermoelectromotrice de ces solutions solides pour etudier l'effet de ZnO sur la conductivite electrique de MnO et la nature des porteurs de charge dans MnO stabilise

Manganese(II) monoxide which is spontaneously oxidized in air is stabilized by solid solution with zinc oxide and then employed as a raw material in the synthesis of manganese(II) zinc ferrites in an inert atmosphere, giving thereby no chance for Mn2+ to get oxidized. Sintering is done in a static controlled atmosphere created by the thermal dissociation of pellets of active iron(III) oxide kept in oxygen-free nitrogen along with the ferrite toroids. The ferrite formation and the sintering are performed at 950 and 1150 °C respectively by employing active oxide raw materials.