INFLUENCE OF PLASMA SYNTHESIS CONDITIONS ON THE ABSORPTION PROPERTIES OF CoyNi1-yFe2O4 FERRITE

Abstract

Cobalt and nickel ferrite nanoparticles have attracted the attention of scientists in recent decades due to their active applications in high-density magnetic recording, magnetic fluids, data storage, solar cells, sensors, and photocatalysis. Cobalt ferrite modified with nickel cations has been widely studied due to its high electromagnetic characteristics, chemical stability, mechanical hardness, and high magnetocrystalline anisotropy. Since most of the magnetic properties of Co_yNi_1-yFe₂O₄ ferrite significantly depend not only on the nickel content, but also on the size and shape of the nanoparticles, the development of new methods for obtaining cobalt ferrites is an important scientific task. In the presented work, the synthesis of Co_yNi_1-yFe₂O₄ by the plasma method was performed. Using a full factorial experiment based on the results obtained by electron paramagnetic resonance (EPR) spectroscopy and X-ray phase analysis, the influence of the pH of the reaction medium, temperature, and duration of plasma treatment was determined. The resonance field from the EPR spectrum and the absorption coefficient from the EPR spectra, crystallite size were used as response functions. The phase composition of the dried powders was determined by the X-ray phase analysis method. The EPR spectra were obtained using a Radiopan SE/X-2543 radio spectrometer. Statistical analysis made it possible to quantitatively assess the influence of synthesis parameters on the selected response functions. Mathematical equations adequately describe the obtained dependencies. The results showed that with increasing treatment time, the intensity of peaks in the EPR spectra decreases significantly, which correlates with the results of X-ray phase analysis and is associated with the formation of non-magnetic phases a-FeOOH, a-CoOOH, Fe₂O₃ H₂O. At the same time, the asymmetry of the EPR spectra increases. The single-component and rather narrow  EPR spectrum of the samples can be explained by the single-phase structure. The highest values of the absorption coefficient correspond to high temperatures in the entire pH range and to the combination of high temperatures and short-term plasma treatment.