Electrical and magnetic characterization of nanocrystalline Ni–Zn ferrite synthesis by co-precipitation route

Magnetic nanocarriers: Evolution of spinel ferrites for medical applications.

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

The dielectric properties of MnxNi0.5−xZn0.5Fe2O4 ferrites with x varying from 0.05 to 0.4 synthesized by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. An increase in the dielectric constant is observed with the increase in Mn concentration except for x=0.3. Dispersion in the dielectric constant with frequency in the range of 100 Hz–1 MHz is observed. Resonance peaks were observed in tan δ∈ versus frequency curves for all samples. A shift in the resonance frequency towards higher frequency is observed with increase in temperature. The peak height also increases with increase in temperature. Possible mechanisms contributing to these processes have been discussed. From the temperature variation of the dielectric relaxation, activation energies for various samples have been calculated and compared with those obtained from dc resistivity.

Dielectric properties of Mn-substituted Ni–Zn ferrites

We have investigated the magnetic and electrical response of the sol-gel synthesized NiFe2O4 nanoparticles. Changes in the impedance plane plots with temperature have been discussed and correlated to the microstructure of the material. Thermally activated hopping carriers between Fe3+-Fe2+ and Ni2+-Ni3+ ions have been determined for a decrease in the resistance of the sample and a change in the conduction mechanism around 318 K. The mixed spinel structure and broken exchange bonds due to small size effects are due to the canted spin structure at the surface of the nanoparticles. The magnetization is found to be influenced by the surface spin canting and anisotropy. We have established the semiconducting to metallic transition (SMT) temperature to be around 358 K in terms of localized and delocalized eg electrons along with a transition from less conductive [Fe3+–O2−–Fe3+] and [Ni2+–O2−–Ni2+] linkage to more conductive [Fe3+–Fe2+] and [Ni2+–Ni3+] linkage at the octahedral B site. A decrease in the dielectr...

Metal-semiconductor transition in NiFe2O4 nanoparticles due to reverse cationic distribution by impedance spectroscopy

Temperature dependence of resistivity, dielectric constant and dielectric loss have been investigated for four different compositions of nickel-zinc ferrites, Nii_IZnIFe2O4 (x = 0.2, 0.35, 0.5 and 0.6), prepared by the citrate precursor technique. Activation energies calculated from the resistivity versus temperature curves for the compositions sintered at 1200 °C and 1300 °C range from 0.55 eV to 0.73 eV. Samples sintered at 1200 °C exhibit higher activation energies and low dielectric losses compared to those sintered at 1300 °C. Samples of the composition with x = 0.6 show low dielectric losses up to a measurement temperature of around 200 °C at higher frequencies as compared to samples of other compositions. The variations in activation energy with composition and sintering temperature have been explained on the basis of the site occupancy in ferrites and the atomic radii of the constituent metal ions.

Temperature dependence of electrical properties of nickel–zinc ferrites processed by the citrate precursor technique

Nickel zinc ferrite of composition Ni0·5 Zn0·5 Fe2O4 was prepared by the citrate precursor method at temperatures as low as 100°C This is much lower than those used in the conventional ceramic method for the preparation of ferrites (~1000°C) The dc resistivity of the sintered specimens was observed to be ~108 Ω cm which is greater, by at least two orders of magnitude, than that for specimens prepared by the conventional method Although the initial permeability values are similar to those for conventionally prepared specimens, the losses are lower and the operational frequency range is larger The significance of the citrate method lies, therefore, in producing ferrites with better properties at reduced processing temperatures

R.G. Mendiratta

Papers

Temperature dependence of electrical properties of nickel–zinc ferrites processed by the citrate precursor technique

Low temperature processing of NiZn ferrite by citrate precursor method and study of properties