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