On the Question of Thermal Stability and Magnetic Properties of Mn0.6Zn0.4Fe2O4 Nanoparticles Prepared by Sol-Gel Method

Mn-Zn ferrite nanoparticles of Mn_0.6Zn_0.4Fe₂O₄ composition were synthesized through sol-gel auto combustion process. The phase formation, thermal stability, morphology, and magnetic properties of as-prepared and heat treated samples have been investigated. It is observed that as-prepared spherical particles (10-40 nm) transform into single phase spinal structure of ~500 nm long cylindrical rods of 60 nm diameter, when annealed at 1200 °C in air. Interestingly, when the samples were annealed at 600 °C in air Fe₂O₃, Mn₂O₃ impurity phases appear along with poor quality ferrite phase. On the other hand, samples annealed at 600 °C, under inert gas conditions showed well-ordered single phase spinal structure with large M_s = 60 emu/g and H_c = 55 Oe. Furthermore, it is shown that on rapid cooling, the sample from 1200 °C yields a good quality spinel structure with enhanced soft magnetic properties (M_s = 62.3 emu/g; H_c = 3 Oe).