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Structural characteristics, electrical conduction and dielectric properties of gadolinium substituted cobalt ferrite

Fine particles of lithium ferrite were synthesized by the sol-gel method. By subsequent heat treatment at different temperatures, lithium ferrites of different grain sizes were prepared. A structural characterization of all the samples was conducted by the x-ray diffraction technique. A grain size of around 12 nm was observed for Li0.5Fe2.5O4 obtained through the sol-gel method. Magnetic properties of lithium ferrite nanoparticles with grain size ranging from 12 to 32 nm were studied. Magnetization measurements showed that Li0.5Fe2.5O4 fine particles exhibit a deviation from the predicted magnetic behaviour. The as-prepared sample of lithium ferrite showed a maximum saturation magnetization of 75 emu g−1. Variation of coercivity is attributed to the transition from multi-domain to single domain nature. Dielectric permittivity and ac conductivity of all the samples were evaluated as a function of frequency, temperature and grain size. Variation of permittivity and ac conductivity with frequency reveals that the dispersion is due to the Maxwell–Wagner type interfacial polarization.

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Structural, magnetic and electrical properties of the sol-gel prepared Li0.5Fe2.5O4 fine particles

Nickel Spinel Ferrites: A review

Nanoparticles of manganese ferrite were prepared by the chemical co-precipitation technique. The dielectric parameters, namely, real and imaginary dielectric permittivity ($\varepsilon'$ and $\varepsilon"$), ac conductivity $(\sigma_{ac})$ and dielectric loss tangent $(tan \delta)$, were measured in the frequency range of 100 kHz–8 MHz at different temperatures. The variations of dielectric dispersion $(\varepsilon')$ and dielectric absorption $(\varepsilon")$ with frequency and temperature were also investigated. The variation of dielectric permittivity with frequency and temperature followed the Maxwell–Wagner model based on interfacial polarization in consonance with Koops phenomenological theory. The dielectric loss tangent and hence $\varepsilon"$ exhibited a relaxation at certain frequencies and at relatively higher temperatures. The dispersion of dielectric permittivity and roadening of the dielectric absorption suggest the possibility of a distribution of relaxation time and the existence of multiple equilibrium states in manganese ferrite. The activation energy estimated from the dielectric relaxation is found to be high and is characteristic of polaron conduction in the nanosized manganese ferrite. The ac conductivity followed a power law dependence $\sigma_{ac} = B\omega^n$ typical of charge transport assisted by a hopping or tunnelling process. The observed minimum in the temperature dependence of the frequency exponent n strongly suggests that tunnelling of the large polarons is the dominant transport process.

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Evidence for polaron conduction in nanostructured manganese ferrite

Temperature and frequency-dependent dielectric properties of Zn substituted Li-Mg ferrites

Infrared spectral studies of Zn-substituted Li–Mg ferrites

Dielectric properties of Cu substituted Ni0.5−xZn0.3Mg0.2Fe2O4 ferrites

Electrical resistivity and thermoelectric power studies on Zn-substituted Li–Mg ferrites

Polycrystalline Li0.5-x/2CdxFe2.5-x/22O4 ferrites wherex = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared by a double sintering ceramic technique and characterized by X-ray diffraction and scanning electron microscopy (SEM). The lattice parameter is found to increase monotonically with the cadmium content. It is explained in terms of the sizes of component ions. The grain size of the samples increases up tox = 0.3 and then it decreases for higher values ofx. A similar trend is observed in the variation of Ms with Cd2+ content. The initial permeability (μi) is however found to increase continuously withx. The increase in μi is attributed to decrease of anisotropy constant K1 and higher grain size of the samples.

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A. M. Shaikh

Papers

Temperature and frequency-dependent dielectric properties of Zn substituted Li-Mg ferrites

Infrared spectral studies of Zn-substituted Li–Mg ferrites

Dielectric properties of Cu substituted Ni0.5−xZn0.3Mg0.2Fe2O4 ferrites

Electrical resistivity and thermoelectric power studies on Zn-substituted Li–Mg ferrites

Cadmium substituted high permeability lithium ferrite