Abstract
Ultrafine $Co_{0.9}Mn_{0.1}Fe_2O_4$ 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.at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Nel temperature $T_N$ was found to be 850 $\pm$ 2 K. Debye temperatures far A and B sites were found to be $\Theta_A = 757 \pm$5K and $Theta_B = 282 \pm$5 K, respectively.
