Ni substitution effect on the structure, magnetization, resistivity and permeability of zinc ferrites

Abstract

Zn_1−xNi_xFe₂O₄ ferrites up to x = 1.0 with Δx = 0.2 have been synthesized via solid state reactions and the sol–gel autocombustion technique with step-by-step co-firing. Data on the chemical composition and the surface morphology of the samples have been obtained using a scanning electron microscope. An X-ray powder diffractometer has been used to establish the phase purity and to determine the unit cell parameters. It has been found that the obtained samples had a spinel structure with the Fdm (No. 227) space group. The unit cell parameters decrease with increasing nickel concentration. The a unit cell parameter decreases almost linearly from ∼8.443 Å for x = 0.0 down to ∼8.337 Å for x = 1.0. The V unit cell volume decreases almost linearly from ∼601.72 ų for x = 0.0 down to ∼579.52 ų for x = 1.0. The magnetic characteristics of the obtained samples are determined and discussed. The Curie point of obtained samples varies in the range of 803.5–572.7 K. The maximum spontaneous magnetization of ∼74.6 emu g⁻¹ at room temperature was fixed for the solid solution with x = 0.6. Ac-resistivity drops by more than 3 orders of magnitude in the frequency range 1–10⁶ Hz. The composition with x = 0.6 has the minimum ac-resistivity of 5.3 kOm cm at a frequency of 10⁶ Hz. The maximum value of the (μ′) real part of ∼11.2 and (μ′′) imaginary part of ∼5.2 of the permeability in the frequency range of 50 MHz–10 GHz is observed for the composition with x = 0.4. The composite samples for the microwave study were prepared by mixing of the ferrite powders with molten paraffin wax. The volume fraction of the ferrite filler in the composites was 25%. The largest value of the (μ′) real part of ∼3 and (μ′′) imaginary part of ∼0.63 of permeability is found for the x = 0.4 composite. The formation of the composite significantly reduces permeability.