The structural and magnetic properties of the nano-CoFe₂O₄ ferrite prepared by sol-gel auto-combustion technique

Single-phased nano-crystalline CoFe₂O₄ ferrite has been prepared using the sol-gel auto-combustion technique. The refinement analyses of X-ray diffraction patterns confirm crystallization of the sample in the (Fd3̅m) space group. The corresponding lattice constant was estimated to be a_exp = 8.37 Å. Theoretical values of other structural parameters such as the ionic radii, bond lengths and the electronegativity at the tetrahedral and octahedral sites have been calculated and compared with values of other spinel systems. The cation distributions indicate that the present system is a partially inversed spinel with inversion factor 0.68. The FT-IR transmittance spectrum has been measured in the range (400–4000) cm⁻¹. It shows the transmittance bands at (575, 1638, 2900 and 3465) cm⁻¹. The 575 cm⁻¹ band has been attributed to the oxygen-metal vibration at the tetrahedral sites. The Energy dispersive X-ray spectroscopy (EDXS) shows the consistency of the weight percentages of the Co and Fe ions with stoichiometric contents within 3% accuracy. Transmission electron microscopy (TEM) has been used in the estimation of the average particle size. The average particle sizes were estimated to be around 95 nm. Values of isomer shifts were found to be in the range (0.29–0.46) mm/s, which indicate that Fe³⁺ oxidation state is dominant and probably low percentage of ferrous Fe²⁺ ions. The saturation magnetization at room temperature was determined to be 69 emu/g and the reduced remanent magnetization value (Mr/Ms) was found to be 0.35. The Yafet-Kittel angle, the blocking (T_B) temperature and Curie (T_C) temperatures were estimated to be 33°, 724 K and 810 K respectively. The high values of T_B and T_C were attributed to the strength of the A-B super-exchange interactions experienced in the CoFe₂O₄ sample.