Dielectric properties such as dielectric constant (ε ε′ ′) and dielectric loss tangent (tan δ δ) of mixed Mn-Zn-Er ferrites having the compositional formula Mn0⋅ ⋅58Zn0⋅ ⋅37Fe2⋅ ⋅05-xErxO4 (where x = 0⋅ ⋅2, 0⋅ ⋅4, 0⋅ ⋅6, 0⋅ ⋅8 and 1⋅ ⋅0) were measured at room temperature in the frequency range 1-13 MHz using a HP 4192A impedance analyser. Plots of dielectric constant (ε ε′ ′) vs frequency show a normal dielectric behaviour of spinel ferrites. The frequency dependence of dielectric loss tangent (tan δ δ) was found to be abnormal, giving a peak at certain frequency for all mixed Mn-Zn-Er ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. Plots of dielectric constant vs temperature have shown a transition near the Curie temperature for all the samples of Mn-Zn-Er ferrites. However, Mn0⋅ ⋅58Zn0⋅ ⋅37Er1⋅ ⋅0Fe1⋅ ⋅05O4 does not show a transition. On the basis of these results an explanation for the dielectric mechanism in Mn-Zn-Er ferrites is suggested.

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The magnetic particles of nickel-zinc ferrite with chemical composition Ni 1−x Zn x Fe 2 O 4 were synthesized successfully by citrate precursor auto-combustion method using high purity nitrates and citric acid as chelating agent. The prepared powder of nickel-zinc ferrites was sintered at 1000˚C for 1 hr to obtain good crystalline phase and was used for further study. The X-ray diffraction technique was employed to confirm the single phase formation of nickel ferrite. The X-ray diffraction pattern shows the Bragg's peak which belongs to cubic spinel structure. The values of lattice constant, X-ray density, bulk density, and porosity were calculated. The temperature dependence of the electrical conductivity plot shows the kink, which can be attributed to ferromagnetic-paramagnetic transition. The activation energy obtained from resistivity plots in paramagnetic region is found to be more than that in ferrimagnetic region. The conduction mechanism in nickel-zinc ferrite particles has been discussed on the basis of hopping of electrons.

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