Magnetic, structural and dc electrical resistivity studies on the divalent cobalt substituted Ni–Zn ferrite system

Abstract

Polycrystalline cobalt substituted Ni – Zn ferrite with composition Ni 0.65-x Co x Zn 0.35 Fe 2 O 4(x = 0.00–0.25 insteps of 0.05) have been prepared through the conventional solid state ceramic method. Calcination and sintering have been performed in air atmosphere at 950°C and 1250°C for 4 h and 2 h, respectively followed by natural cooling to room temperature. X-ray diffraction patterns of all samples indicated the formation of the single spinel structure and the accurate lattice parameter for each composition has been determined using the Nelson–Riley error function. The increase in lattice constant on cobalt substitution is attributed to the ionic radius difference between the displaced and the substituted ion. The variation in lattice constant on incorporation of Co 2+ ion indicates its solubility into the spinel lattice and noticeable modification in structural properties have been observed. The observed increase in the saturation magnetization and Curie temperature with the increase in the Co 2+ substitution is due to its higher magnetic moment compared to that of Ni 2+, improvement in the A–B exchange interaction mechanism and large positive contribution to magnetic anisotropy due to presence of Co 2+ when they are at the octahedral sites. The observed variation in the initial magnetic permeability and the magnetic loss factor with cobalt substitution measured at a low frequency of 1 KHz have been attributed to the modification in the density, porosity, grain size and anisotropy contributions. A nearly comparable variation is observed in the room temperature dc electrical resistivity and activation energy for conduction and is attributed to the modification in structure, role and nature of cobalt ions and the microstructure aspects like grain size and pore concentration. The activation energy values in the range of 0.28 to 0.36 eV suggest a possible electron hopping. The observed changes in the structural and the magnetic and electrical properties have all been discussed in the light of exiting understanding.