Growth of ultrafine Co-Mn ferrite and magnetic properties by a sol-gel method

Ultrafine Co0.9Mn0.1Fe2O4 particles are fabricated by a sol-gel method. Mag netic and structural properties of powders are investigated with x-ray diff raction, vibrating samples magnetometer, and Mossbauer spectroscopy. Co-Mn ferrite powders which were fired at and above 673 K have only a single phas e spinel structure and behave ferrimagnetically. Powders annealed at 673 K have a typical spinel structure and the paramagnetic and ferrimagnetic natu re, simultaneously. The formation of nanocrystallized particles is confirme d when Co-Mn ferrite is annealed at 623 K. The magnetic behavior of Co-Mn f errite powders fired at and above 823 K shows that an increase of the annea ling temperature yields a decrease of the coercivity and an increase of the saturation magnetization. The maximum coercivity and the saturation magnet ization of Co-Mn ferrite powders are 1523 Oe and 66.7 emu/g, respectively. Fe-57 Mossbauer spectra of Co-Mn ferrite have been taken at various tempera tures from 13 to 850 K. The isomer shifts indicate that the valence states of the Fe ions have a ferric character. (C) 1999 American Institute of Phys ics. [S0021-8979(99)53608-6].