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 1C in air, and had poor magnetic properties. However, Fe2O3 and Mn2O3 were dissolved after ferrites annealing above 1100 1C. Moreover, the 1200 1C annealed sample showed pure ferrite phase, larger saturation magnetization (Ms=48.15 emug ) and lower coercivity (Hc=51Oe) compared with the auto-combusted ferrite powder (Ms=44.32 emug , Hc=70Oe). The 600 1C air annealed sample had the largest saturation magnetization (Ms=56.37 emug ) and the lowest coercivity (Hc=32Oe) due to the presence of pure ferrite spinel phase, its microstructure and crystalline size. & 2009 Elsevier B.V. All rights reserved.