Temperature dependent structural, optical, magnetic and dielectric characteristics of cobalt nanoferrites

Spinel nanoferrites have gained tremendous research interest in the field of biomedical applications and memory devices. We present detailed studies on the microstructure and nanoscale properties of high purity cobalt ferrite nanomaterials, which were prepared by the citrate precursor method at varying annealing temperatures. XRD measurements showed an increase in the crystallite size from 29 to 40 nm with the increase in annealing temperature from 500 to 700°C. Field emission scanning electron microscopy (FESEM) and transmission eletron microscopy (TEM) analysis revealed the average grain size between 0.092 and 0.129 µm and particle size of 102 nm of the synthesized cobalt nanoferrite. Energy dispersive X-ray (EDX) analysis confirmed the presence of Co, Fe and O with appropriate stoichiometric ratio in synthesized nanoferrite. Fourier-transform infrared spectroscopy identified the metal oxide bonds between 465 and 579 cm⁻¹ in these nanoferrites. The energy band gaps decrease from 3.77 to 3.26 eV with the increase in annealing temperature as measured using UV–Visible spectroscopy. Photoluminescence study indicates the radiative defects and oxygen voids in CoFe₂O₄ nanocrystals present in the synthesized samples. With the increase in temperature, the magnetic parameters like saturation magnetization, coercivity, etc. shows significant changes. The increase in annealing temperature resulted in the reduction of capacitance, dielectric constant and loss tangent values in the frequency range of 100 Hz–5 MHz which is measured using impedance analyser on the palette samples. The observed magnetic parameters, oxygen vacancies and low dielectric loss may facilitate these materials for their possible use in bio-inspired nanorobotic, hydroelectric cells and high frequency applications.