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Magnetism in Cu_1-xCd_xFe₂O₄ ferrites (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) was measured using an ac susceptibility technique and the vibrating sample magnetometer. The orientation of spins at octahedral and tetrahedral sites and Y–K angles have been measured. For samples having x = 0.0, 0.1 and 0.2, the Y–K angle is measured to be zero and the samples follow Neel's collinear model. For samples having x=0.2 a triangular spin arrangement on B-sites weaken the AB-interaction. Magnetic behaviour of these ferrite is predicted on the basis of the abovementioned observations.

Ultra fine NiAl_xFe_2-xO₄(0 ≤ x ≤ 1) nanopowders were synthesized by sol-gel method and their structural properties were investigated using X-ray diffractometer (XRD) and fourier transform infrared (FTIR) spectrometer. The particle size D, lattice constant a, density dx decreased with increasing non-magnetic Al content x. The combustion reaction mechanisms were explained with the help of FTIR analysis.

The physico-chemical, structural and electrical properties of zinc substituted copper ferrites having the general formula Cu_1-xZn_xFe₂O₄(x=0.0 to x=0.8) have been studied as a function of zinc ion concentration. The sample was prepared by co-precipitation method from corresponding metal sulphates. X-ray diffraction patterns were used to confirm the structure of synthesized samples. The calculated and theoretical values of average lattice constant, tetrahedral bond, tetrahedral edge and unshared octahedral edge were found to increase, while the shared octahedral edge and octahedral bond decrease as the Zn ion concentration increases. The dielectric constant (ε′) and dielectric loss tangent (tan δ) were measured at a constant frequency 1 kHz as a function of temperature. The dielectric constant and loss tangent were found to increase with rise in temperature. The conduction mechanism in these ferrites is discussed on the basis of electron exchange between Fe²⁺ and Fe³⁺ ions. The temperature dependent dc resistivity was carried out in the temperature range 300 to 800 K. The plots of log ρ versus 10³/T are linear showing two regions, corresponding to ferrimagnetic and paramagnetic regions.

The editorial board discovered that the data points in several sections of the Mossbauer spectra as given in Figs. 3(a) and 3(b) are exactly identical. This is impossible and nonphysical for the measurement of two different samples (or for that matter not even for the same sample!). The only conclusion we can draw from this figure is that some of the data is fabricated. As a result, the results and conclusions as described in the paper are unacceptable. This article is retracted from its publication in Int. J. Mod. Phys. B.

In this paper we report influence of titanium substitution on the structural properties and d.c. conduction behavior of Li-Zn ferrites. The samples having the compositional formula Li_0.45+0.5tZn_0.1Ti_tFe_2.45-1.5tO₄ with t varying from 0 to 1.2 in steps of 0.2 were prepared by the conventional dry ceramic method. XRD analysis showed all the samples to be single phase spinel and the lattice parameter was found to increase with increasing t. D.C. resistivity increases with Ti concentration. The possible mechanisms involved are discussed.

Li_0.45Ni_0.1Mn_0.1Fe_2.35O₄ ferrite samples were prepared by microwave-sintering (MS) and conventional (CS) techniques. XRD studies have confirmed the single-phase spinel structure of the sample. The lattice constant was found to be 8.334 Å which is lower than that of the conventionally sintered (CS) sample. Upon microwave sintering, improved physical and electrical properties (like density, resistivity etc.) were obtained. A comparative study has been made on the dielectric behavior of samples processed by both techniques. The possible mechanisms are discussed.

The effect of cadmium substitution and sintering temperature on the microstructure and dielectric properties of nano ZnCd_xFe_2-xO₄ ferrites (x=0.0, 0.05, 0.1, 0.2, 0.3 and 0.5) has been investigated and prepared by egg-white technique. Electrical conductivity and dielectric measurements have been analysed in the frequency range from 100 Hz to 10 MHz. The variation of the real (ε′) and imaginary (ε″) part of dielectric constant, AC conductivity (σ_AC) and loss tangent (tan δ) with frequency has been studied. It follows the Maxwell–Wagner model based on the interfacial polarization in consonance with the Koop's phenomenological theory. It is found that the permittivity of ZnCd_xFe_2-xO₄ ferrites improved and shows a maximum value (~9 × 10³) at 100 Hz for the x=0.1 sample.

Ni substituted Li–Zn ferrites with compositional formulas Li_0.4-0.5xZn_0.2Ni_xFe_2.4-0.5xO₄, where x = 0.02 ≤ x ≤ 0.1 in steps of 0.02, is synthesized by a chemical method using citrate precursors. The prepared ferrites are investigated for their structural, electrical and magnetic properties. Ni substitution significantly changes the characteristic properties of Li–Zn ferrites. There is an increase in grain growth as determined from SEM measurements. An increase in the room temperature DC resistivity is observed with the addition of Ni. The room temperature initial permeability shows an overall decrease with Ni concentration, which is explained with respect to saturation magnetization and supplemented by nuclear hyperfine field obtained from Mössbauer analysis. The variation of the complex permeability with frequency is measured over the frequency range of 100 Hz–1 MHz and dispersion is found. A possible mechanism contributing to the above process is discussed.

Ni–Cu–Zn ferrite materials have been extensively used in multilayer chip inductors because of their remarkable properties at higher frequencies. In the present work, single phase Ni_0.35Cu_0.05Zn_0.60Fe_1.98O_4-δ ferrite, has been prepared by microwave sintered (MS) method. In comparison with the conventional sintering method (CS), the sintering temperature and time for this MS method were significantly reduced to 30 min and 950°C from 5 h and 1250°C for the CS process. The frequency dependence of the dielectric properties such as dielectric constant (ε'), dielectric loss (tan δ) were studied. The temperature dependence of magnetic initial permeability (μ_i) was studied. The saturation magnetization was also studied as a function of magnetic field. These microwave sintered ferrites results were compared with the properties of ferrites prepared by conventional sintering method in normal heating. Microwave sintering improves structural as well as electromagnetic parameters measured and thus makes the ferrite more suitable in microwave applications and electromagnetic devices.

Li–Co nanoferrites (Li${}_{0.5-x/2}$Co${}_x$Fe${}_{2.5-x/2}$O₄) with x = 0.00, 0.03, 0.06, 0.09, and 0.12, were synthesized by chemical sol–gel method. Two different sintering techniques viz. conventional technique (CT) and microwave technique (MT) were employed to heat treat the synthesized samples with an aim to study the effect of sintering technique on the properties of the nanoferrites. Structural and microstructural properties of the samples were investigated using XRD and scanning electron microscopy (SEM) technique, respectively. The variation of room temperature dielectric constant and dielectric loss were measured as a function of frequency in the range 100 Hz–1 MHz and the normal dispersive behavior was observed. Magnetic properties were investigated using Vibrating Sample Magnetometer (VSM), while Soohoo’s method was used to measure Curie temperature. The results obtained have been discussed in the paper.

The structural properties of Vanadium Ferrite VFe₂O₄ are reported for temperature range 0–1000 K using Density Functional Theory. A comparative study with the available experimental and theoretical data in the literature is also presented. Effects of temperature on lattice constant, volume and bulk modulus are deduced that with the increase in temperature, bulk modulus decreases and lattice constant slightly increases. This proves that the material VFe₂O₄ remains in the same cubic phase for temperature range 0–1000 K. In addition, the optical response is observed with six optical constants like absorption, reflectivity, eloss, dielectric functions, refraction and optical conductivity. Band structures and electronic density of states are also computed by using TB-mBJ potential. We hope that our findings would provide a help to experimentalists in fabricating VFe₂O₄ for temperature-sensitive optical devices.

Superparamagnetic (SP) crystalline cobalt ferrite (CoFe₂O₄) nanoparticles are synthesized by chemical co-precipitation method. Grown nanoparticles are annealed in air at various temperatures in the range 373 K to 1173 K to understand the variation in properties in nanoregion. Physical properties are analyzed for crystalline phase, crystallite size, particle size, shape, magnetization and relaxation behavior by using various characterization techniques viz. X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR). Annealing effect on various physical properties of particles are investigated. Particles are used in the development of stable ferrofluid.

The scope of the present work is in enhancing the particle size, and dielectric properties of Mg-substituted Cobalt ferrites nanoparticles prepared by sol–gel auto combustion method. The different ratios of Mg-substituted Co Ferrites (Co${}_{1-x}$Mg_xFe₂O₄($x=0.00$, 0.05, 0.10, 0.15, 0.20 and 0.30)) are calcinated at 850${}^{\circ }$C. The synthesized nanoparticles were characterized by powder XRD, FTIR, FE-SEM, EDX techniques and dielectric behavior. The structural parameters were confirmed from powder XRD and the average particle size is obtained from 39 to 67 nm due to the substitution of Mg${}^{2+}$ which was calculated by Debye Scherrer’s formula. FE-SEM showed the surface morphology of the different ratio of the sample. The dielectric loss has measured the frequency range of 50Hz–5MHz. From electrical modulus, conductivity relaxation and thermal activation of charge carriers has been discussed.

Ferrite nanoparticles of Ni${}_{0.35}$Mn${}_{0.35}$Zn${}_{0.3}$Fe${}_{2-x}$Ce_xO₄ ferrite system were produced using sol–gel auto combustion technique. X-ray diffraction analysis confirms the single phase cubic spinel structure of the samples with space group Fd-3m. Replacement of Fe${}^{3+}$ ions by Ce${}^{3+}$ ions increases the lattice parameter 8.4105 Å to 8.4193. Average crystallite size obtained from Scherrer method varies from 21.73nm to 22.71nm with replacement of Fe${}^{3+}$ ions by Ce${}^{3+}$ ions. Williamson–Hall and strain-size plot analysis confirms the nanocrystalline nature of the samples and the micro-strain induced in the cubic crystals is of tensile type. Cation distribution suggests that Zn${}^{2+}$ ions occupy tetrahedral — A-site while Ni${}^{2+}$ ions occupy octahedral — B-site. Majority of the Mn${}^{2+}$ ions prefer A-site and majority of the Ce${}^{3+}$ ions replace Fe${}^{3+}$ ions at octahedral — B-site. High resolution transmission images confirm the homogeneity and nanoparticle nature of the samples. Two main characteristics absorption bands corresponding to spine structure are observed in the Fourier transmission infra-red spectra within the wavenumber range of 350–600cm${}^{-1}$. Stiffness constant, Young’s modulus, rigidity modulus, bulk modulus and Debye temperature were estimated using FTIR data. Debye temperature obtained from the Waldron equation varies from 676K to 692K with the addition of Ce${}^{3+}$ ions. Higher values of elastic moduli are suitable for industrial applications due to increased mechanical strength.

The multiferroic (Bi_0.95RE_0.05)(Fe_0.95Mn_0.05)O₃ (where RE = Pr, Tb and Dy) has been synthesized using solid-state reaction technique. Effects of Pr, Tb and Dy substitution on the structure, electrical and ferroelectric properties of (Bi_0.95RE_0.05)(Fe_0.95Mn_0.05)O₃ samples have been studied by performing X-ray diffraction, dielectric measurements and magnetic measurements. The crystal structure of the ceramic samples have a monoclinic phase. The vibrating sample magnetometer (VSM) measurement shows a significant change in the magnetic properties of Pr-, Tb- and Dy-doped (Bi_0.95RE_0.05)(Fe_0.95Mn_0.05)O₃. It is seen that coercive field (H_c) and remanent magnetization (M_r) increases for Pr but decreases for Dy and Tb.

The compositional dependence of ac conductivity (${\sigma }_{\mathrm{\text{ac}}}$), real ($\sigma$′) and imaginary ($\sigma$′′) parts of complex electric conductivity ($\sigma$*) was investigated as a function of temperature ($T$) and frequency ($f)$ for Mn${}_{0.7{+x}_{}}$Zn${}_{0.3}$Si_xFe${}_{2–{2x}_{}}$O₄, $x=0.0$, 0.1, 0.2 and 0.3 spinel ferrite system. The compositional dependence of lattice constant values suggested that the most of the substituted Si${}^{4+}$-ions reside at grain boundaries and only a few Si-ions are inside grains. The variation of ${\sigma }_{\mathrm{\text{ac}}}(x$, $f$, $T)$ is explained on the basis of segregation and diffusion of Si${}^{4+}$ ions at grain boundaries and grains, respectively, and the electrode effect. Thermal variation of ac conductivity at fixed frequency suggested two different mechanisms which could be responsible for conduction in the system. It is found that $\sigma$* is not the preferred presentation for dielectric data and the scaling process of real part of conductivity by normalized frequency and the scaled frequency were found unsuccessful. The fitting results of ac conductivity data with path percolation approximation were found suitable in low-frequency regime while in high-frequency regime, effective medium approximation (EMA) was found successful.

Spinel ferrite ${\text{Ni}}_{0.08}$${\text{Mn}}_{0.90}$${\text{Zn}}_{0.02}$Fe₂O₄ was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050${}^{\circ }$ C, 1100${}^{\circ }$ C and 1150${}^{\circ }$ C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm${}^{-1}$ to 400 cm${}^{-1}$. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 $\mu$m to 0.88 $\mu$m. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity ($H_c)$ and saturation magnetization ($M_s)$. Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature ($T_c)$ and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.

Single phase nanocrystalline soft magnetic Mg_0.7-xNi_0.3Zn_xFe₂O₄, ferrites with x = 0.0 − 0.7 were prepared by sol gel auto-combustion method. X-ray diffraction confirms the formation of single phase nano-crystalline cubic spinel ferrites with average grain diameter ranging between 12.9 nm to 23.9 nm. Formation of the ferrite phase without subsequent heat treatment makes sol-gel auto combustion technique especially suitable and economical for the large scale industrial production of the nano-crystalline ferrites for multilayer chip inductor applications (MLCI). Both, lattice parameter and X-ray density shows a linear increase with increasing Zn²⁺ concentration, attributed to the difference in ionic radii and density of Mg and Zn. Increase in Zn content enhances the soft magnetic behavior, exhibiting linear decrease of coercivity from 122.34 Oe to 72.45 Oe, explained by increase of density with Zn addition. The maximum magnetization (M_max)increases up to 0.106 Tesla (for x = 0.4) and. then decreases with increase of Zn content, discussed on the basis of increase of the occupancy of A-site in spinel ferrite by non-magnetic Zn²⁺ ion.

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.

The influence of iron non-stoichiometry variation on structural, magnetic and dielectric properties in Cobalt ferrite is reported. Cobalt ferrite with compositional formula CoFe${}_{2\pm x}$O₄ ($x=0$, $\pm 0.02$) was prepared through sol-gel synthesis route and sintered at 900^oC/2h. X-ray diffraction confirms the phase evolution of ferrite with additional impurities belonging to $\alpha$-Fe₂O₃ phase and this additional phase disappears for iron deficient sample. The (311) peak shifts towards lower angle for the excess iron sample, whereas it shifts towards higher angle for iron deficient one, confirming the variation in the iron non-stoichiometry. Raman data substantiate the presence of vibrational bands assigned to metal ions in the cobalt ferrites. Change in the peak intensities and peak angle in Raman spectra clearly suggests the movement of cations among octahedral and tetrahedral sites leading to dilution of magnetic character of the samples. Saturation magnetization drastically drops by $\sim 20$% for iron rich and deficient samples but an improvement in coercivity for the iron deficient cobalt ferrite clearly hints the role of anisotropy. A change in dielectric constant value further alludes to the change of iron ions in different valency states.