Variation in magnetic and structural properties of Co-doped Ni–Zn ferrite nanoparticles: a different aspect

Cobalt-substituted nickel–zinc ferrite nanoparticles (Ni_0.6−x Zn_0.4Co _x Fe₂O₄) (x = 0, 0.0165, 0.033, 0.264 and 0.528) have been synthesized and characterized with respect to their structural and magnetic properties. Exceptionally in spite of the reported literature where the saturation magnetization increases with Co doping that attributes to Co²⁺ ions distribution in octahedral sites, the saturation magnetization in our samples decreases by increasing Co contents as revealed by vibrating sample magnetometer measurements. To know the structural properties such as phase identification, measurement of crystallite size and other structural parameters, prepared samples have been performed by X-ray diffraction technique. The X-ray diffraction spectra measurements show that samples have single-phase spinel cubic structure at x = 0, 0.033, 0.264 and 0.528, and at x = 0.0165, there is partial formation of hematite phase. The uncommonly decreased saturation magnetization, variation in retentivity, coercivity and magneto-crystalline anisotropy and also variation in structural properties with Co doping are explained on the basis of Co²⁺ ions distribution in tetrahedral and octahedral sites in place of Ni²⁺ and Zn²⁺ ions having different magnetic moments and different ionic radii, respectively. Using transmission electron microscopy, the particles size has been calculated. The morphology and stoichiometry of prepared samples have been investigated by field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy techniques, respectively. The structural and magnetic measurement results are well co-related with each other with respect to Co²⁺ ions doping and its distributions. The moderate saturation magnetization and low coercivity values of all samples show soft magnetic behavior and attribute the usefulness of these materials in magnetic recording devices.