Study on structural, optical and magnetic properties of cobalt substituted magnetite nanoparticles for ferrofluid applications

Abstract

Cobalt substituted magnetite nanoparticles having the composition CoxFe3−xO4 (0.0 ≤ x ≤ 0.4 in steps of 0.2) have been prepared using co-precipitation method. Various structural, microstructural, optical and magnetic characterizations have been carried out using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FESEM), UV–Visible spectroscopy and Vibrating sample magnetometer (VSM) respectively. The spinel structure of the synthesized nanoparticles has been confirmed using XRD technique and Rietveld refinement techniques. Crystallite size calculated from Scherrer’s and Williamson – Hall (W-H) methods are in agreement and found to decrease from 15 nm to 10 nm with increase in cobalt substitution. The ultrafine nano crystallite is desirable for ferrofluid preparation. Lattice strain is obtained from the slope of the linear fit in the W-H plot. FTIR spectra reveals two absorption bands around 540–420 cm−1 which corresponds to the vibrations of the MO bonds at the tetrahedral and octahedral sites respectively, and is characteristic of the ferrite samples. The average particle size obtained from FESEM measurement is found to be in the range 15 nm to17 nm. UV–Visible spectroscopy shows maximum absorption around 380–400 nm. Optical band gap of the samples estimated using Tauc plot is found to be in the range 2.10 eV to 2.55 eV. The saturation magnetization of the samples is found to be in the range 57 emu/g to 60 emu/g. Stable aqueous ferrofluids of the nanoparticles have been obtained using tetramethyl ammonium hydroxide as the ionic surfactants.