Control of structural and magnetic characteristics of cobalt ferrite by post-calcination mechanical milling

Abstract

The possibility to control the structural parameters of nanostructured spinel cobalt ferrite paves the way to prepare the ferrite with the anticipated magnetic properties for broad applications. This study is aimed at elucidating the correlation between structural parameters and magnetic properties of cobalt ferrite nanoparticles subjected to post-calcination high-energy ball milling. The milling energy was predicted at four different levels, using the standard collision model. The samples produced were characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometry (VSM). Both FTIR studies and Rietveld refinement of the XRD data shows re-distribution of cations in the spinel structure, induced by a critical level of milling energy. Also, the presence of the three ionization peaks, Co−2p, Fe−2p and O−1s, revealed by XPS confirms the formation of spinel ferrite structure in the cobalt ferrite nanoparticle. The maximum energy products (BH)max of the sample milled under high level ball milling energy was 2.18 MGOe which is almost 5 times higher than that of the un-milled calcined sample. Additionally, the magnetic anisotropy constant was calculated by the Law of Approach to Saturation (LAS) method and indicates a direct correlation between lattice strain and coercivity of samples.