Structural and Magnetic Properties of Co - Mn Ferrite Prepared by a Sol - gel Method

Ultrafine Co_(0.9)Mn_(0.1)Fe₂O₄ powders have been fabricated by a sol-gel method. Structural and magnetic properties of the powders were investigated by x-ray diffractometry, transmission electron microscopy (TEM), Mossbauer spectroscopy, and vibrating sample magnetometry (VSM). Co-Mn ferrite powders that were fired at and above 773 K contained only a single spinel phase and behaved ferrimagnetically. Powders fired at 673 and 723 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. The magnetic behavior of Co-Mn ferrite powders fired at and above 873 K showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum saturation magnetization and coercivity of Co-Mn ferrite powders were 66.7 emu/g and 1523 Oe, respectively. Mossbauer spectra of the powder fired at 923 K were taken at various temperatures ranging from 13 to 850 K. The iron ions oat both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Neel temperature T_N was found to be 850±2 K. Debye temperatures for A and B sites were found to be Θ_A=757±5 K and Θ_B=282±5 K, respectively.