The effect of heat treatment temperature on the microstructure and magnetic properties of Ba₂Co₂Fe₁₂O₂₂ (Co₂Y) prepared by sol-gel method

Ferroxplana type hexagonal ferrite with composition Ba₂Co₂Fe₁₂O₂₂ (Co₂Y) was prepared by polymeric sol-gel method from the aqueous solution of their corresponding metal salts. All the samples were characterized by using X-ray diffraction and scanning electron microscopic technique. The formation and the microstructure of the Ba₂Co₂Fe₁₂O₂₂ was studied as a function of heat treatment temperature and it was observed that well defined hexagonal plate-like fine particles with particle sizes between 130 and 400 nm were formed at relatively lower temperature (900 °C) as compared to conventional solid state reaction method (1100 °C). Magnetic properties of the samples were also studied as a function of heat treatment temperature and it showed large saturation magnetization (M_s) ranging from 30.9 to 47.6 emu/g and a wide range of coercivity (130∼1566 Oe) depending on the heat treatment temperature. The very high saturation magnetization at relatively lower temperature (say 800 °C) arises due to the presence of several high magnetic impurities, such as BaFe₁₂O₁₉ and CoFe₂O₄. The saturation magnetization increases with increasing heat treatment temperature above 900 °C, while the coercivity showed a reversed order.