Structural, Magnetic and DC Electrical Resistivity Studies of Ni–Zn–Cr Ferrites Prepared by the Citrate-Gel Auto-Combustion Method

Abstract

Nanocrystalline chromium substituted Ni–Zn nanoferrites with composition Ni0.5Zn0.5CrxFe2−xO4 (0 ≤ x ≤ 0.25, in steps of 0.05) have been synthesized using citrate-gel auto-combustion method. The as synthesized powder of the starting composition has been characterized by using TG–DTA in air atmosphere for the temperature up to 800 °C and X-ray diffraction for its structure. Upon confirming the spinel phase for the starting composition, the chromium substituted Ni–Zn ferrite nano powders were synthesized by the similar procedure. The as synthesized powders were pressed into pellets and toroids under uniaxial pressure followed with sintering in air atmosphere for 4 h at 1100 °C for electrical and magnetic characterizations. The X-ray diffraction studies revealed a decrease of the lattice constant and considerable modification in the structure of Ni–Zn ferrite with the substitution of Cr3+ for Fe3+ ions. The room temperature FT-IR spectra displayed three significant IR absorption bands in the wave number range of 350–600 cm−1 which is a characteristic of the spinel structure. The band positions and intensities were found to vary with chromium substitution in Ni–Zn ferrite. The room temperature DC electrical resistivity and activation energy for conduction in the Ni–Zn–Cr ferrite samples were measured by using the two-probe method while the AC resistivity studies were carried out in the frequency range of 1 kHz to 13 MHz and the all the observations have been discussed in the light of existing understanding.