Heat treatment effects on microstructure and magnetic properties of Mn-Zn ferrite powders

Mn-Zn ferrite powders (Mn0.5Zn0.5Fe2O4) were prepared by the nitrate-citrate auto-combustion method and subsequently annealed in air or argon. The effects of heat treatment temperature on crystalline phases formation, microstructure and magnetic properties of Mn-Zn ferrite were investigated by X-ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy and vibrating sample magnetometer. Ferrites decomposed to Fe2O3 and Mn2O3 after annealing above 550 degrees C in air, and had poor magnetic properties. However, Fe2O3 and Mn2O3 were dissolved after ferrites annealing above 1100 degrees C. Moreover, the 1200 degrees C annealed sample showed pure ferrite phase, larger saturation magnetization (M-s=48.15 emu g(-1)) and lower coercivity (H-c=51Oe) compared with the auto-combusted ferrite powder (M-s=44.32 emu g(-1), H-c=70 Oe). The 600 degrees C air annealed sample had the largest saturation magnetization (M-s=56.37 emu g(-1)) and the lowest coercivity (H-c=32 Oe) due to the presence of pure ferrite spinel phase, its microstructure and crystalline size. (C) 2009 Elsevier B.V. All rights reserved.