Phase Formation and Crystallinity-Dependent Magnetic Parameters of Co1-xFe2+xO4 Nanoparticals

Abstract

Nano crystalline cobalt ferrite CoFe2O4 powders were synthesized using the coprecipitation method. The effect of the calcination temperature and the Fe3+/Co2+ molar ratio on the phase formation, macro and microstructure and magnetic properties was studied systematically. The Fe3+/Co2+ was controlled to equal 2 and 2.75 while the annealing temperature (Ta) was adjusted to vary from 600 to 1000Co. the obtained powders were investigated using x-ray diffraction (XRD) analysis, Field emission scanning electron microscope (FESEM), Fourir transformation infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). For both the Fe3+/Co2+ ratios, the XRD results indicat the formation of well crystallized cubic spinel cobalt ferrite phase for the precursors annealed at 600Co up to 1000Co. However a second rhombohedral hematite phase whose content varies respectively from 3% and 15% was formed as the Fe3+/Co2+ varied from 2 to 2.75 at Ta=800 and 1000Co. The crystallite size (Dβ) as determined applying the win-fit program was found also to decrease from 54.5 to 48.6nm accompanied by an increase of the root mean square strain < eg>. Using Rditveld analysis no effect on the value of the lattice parameter (a) was detected. The FESEM micrographs reveal the formation of highly agglomerated particles for Fe3+/Co2+ =2.75 and Ta =1000Co. The FTIR analysis confirm the formation of the spinel structure phase for both Fe3+/Co2+ ratios at 1000Co, however the absorption bands shift to higher frequencies for Fe3+/Co2+ =2.75. Other bands at 1663 and 3472cm-1 ascribed to free or absorbed water molecules were also detected for this ratio. The Fe3+/Co2+ molar ratio was found to have a significant effect on the magnetic properties of the produced cobalt ferrite. The calculated magnetic parameters: the saturation magnetization (MS= 71.219emu/g), the coricivity (HC= 1443.8Oe) and the remanence ratio (Mr/MS= 0.405) were recorded to decrease as the Fe3+/Co2+ increases except for the curie temperature (TC) which increase from 405 to 410Co.