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The systems MgCuZnFe₂O₄ doped (0–0.6 wt% Ta) are prepared by the general ceramic method using the sintering temperature at 1200°C. The variations of the sintered density, lattice parameter, jump length of electrons, and initial permeability were studied. A maximum density was obtained at 1200°C during the preparation process. The electrical resistivity decreases with increasing tantalum (Ta) content upto 0.1 wt% and then increases for higher concentrations. The initial permeability and the change carries mobility increase upto 0.1 Ta and then decreases. The jump length decreases with enhancing Ta ions because the substitution of Ta ion with small size instead of Fe³⁺ at the A sites increase the concentration of iron ions at the B sites. The increase of the iron content causes the decrease of the jump length of electrons between Fe³⁺ and Fe²⁺. These improvements of the magnetic properties give some light about the importance of these compositions to be used in technology.

Li–Ni–Co ferrite samples with compositional formula Li${}_{0.45-0.5x}$Ni${}_{0.1}$Co${}_x$Fe${}_{2.45-0.5x}$O₄ with $x$ ranging from 0.00 to 0.1 in steps of 0.02 were prepared by sol–gel method. X-ray diffraction (XRD) analysis confirmed the formation of single phase with spinel structure in all the samples. The lattice constant evaluated from XRD data was found to increase with increase of Co${}^{2+}$ substitution and crystallite size was observed in the range of 30–59 nm. The microstructure of the samples was studied by using scanning electron microscopy (SEM). Nanocrystalline nature of ferrites was also confirmed by transmission electron microscopy (TEM). $M$–$H$ measurements were made using a vibrating sample magnetometer and hysteresis parameters such as saturation magnetization and coercivity were obtained for all compositions. The frequency variations of initial permeability and permeability loss showed a dispersive behavior for all compositions and an increase in initial permeability is observed with increase of Co${}^{2+}$ substitution. The results obtained and mechanisms involved are discussed in the paper.

Processing of ferrites has gained tremendous importance in recent times in order to meet high performance demands on ferrites in keeping with the fast emerging technologies. The main focus of research in the 21st century is towards the formation of smaller magnetic particles. In normal ceramic methods we cannot control particle size and porosity, whereas in precursor methods we can control both. In the present study we have synthesized Mg_0.9Mn_0.1Fe₂O₄ ferrites by the normal ceramic method and the citrate precursor method. By the citrate method we have simultaneously reduced the particle size and sintering temperature as compared to the normal ceramic method. By the citrate method, direct current (DC) resistivity is increased by two orders of magnitude, and electrical as well as magnetic losses are reduced as compared to the normal ceramic method. The initial permeability is reduced in both citrate method as compared to the normal ceramic methods. However, with sintering temperature the initial permeability increases. The dielectric constant is reduced by the citrate method as compared to normal ceramic methods. These observations are explained on the basis of various mechanisms and models.

Active powder of Cu-substituted Mn-Zn ferrite was synthesized by soft chemical approach called co-precipitation method. The initial permeability, density, grain size, Curie temperature and dc resistivity were studied. X-ray diffraction (XRD) method confirmed the sample to be a single-phase spinel and of nano-structure (~ 65 nm). Further, scanning electron micrograph (SEM) also confirmed nano-phase and the uniformity of the particles. The initial permeability values did not exhibit much variation with temperature, except near Curie temperature where it falls sharply. The initial permeability was found to increase with the increase in sintering temperature. This is attributed to the increase in the grain size.

Polycrystalline nickel–zinc ferrites of chemical formula Ni_0.65-xMg_xZn_0.35Fe₂O₄ (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.

In the present work, Al${}^{3+}$ substituted cobalt ferrites (CoFe${}_{2-x}$Al_xO₄, $x=0.2$, 0.4, 0.6, 0.8) have been synthesized via standard solid-state reaction technique. The incorporation of Al${}^{3+}$ ions in cobalt ferrite has been shown to play an important role in modifying the magnetic properties. The room temperature (300K) ${}^{57}$Fe Mössbauer spectra reveals that the studied samples show two characteristic ferromagnetic zeeman sextets at A and B-sites at lower Al${}^{3+}$ ion concentration (i.e., up to $x=0.4$). However, a paramagnetic relaxation has been noted for higher Al${}^{3+}$ substitution (for $x=0.6$ and 0.8) samples. The dependence of the Mössbauer parameters such as isomer shift, quadrupole splitting, line width and magnetic hyperfine field on Al${}^{3+}$ ion concentration has also been noted. The variations in initial permeability over a wide frequency range (125kHz to 30MHz) at 300K have been recorded. The fairly constant values of initial permeability and the low values of the relative loss factor of the order of 10${}^{-4}$ to 10${}^{-5}$ over the wide frequency range are the important findings of the present work. The observed low values of relative loss factor at high frequencies suggest that the studied ferrites are promising materials to be used in microwave applications.