Temperature-Dependent Variations in Structural, Magnetic, and Optical Behavior of Doped Ferrites Nanoparticles

Nanocrystalline Mn-Zn ferrite nanopowders (Mn_0.5Zn_0.5Fe₂O₄) were synthesized by co-precipitation technique and post-fabrication annealing has been performed at different temperature ranges from 400 to 700 °C for 2 h. The effect of annealing on morphology, crystalline phase formation, cation distribution, lattice constant, particle size, magnetic properties, and optical properties was studied by scanning electron microscopy (SEM), x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and UV-visible spectroscopy (UV-Vis) respectively. The crystallite size increased from 14 to 24 nm with the annealing temperature owing to the grain growth process or more technically we say Ostwald ripening mechanism. The decomposition of ferrites at low-temperature results in the formation of hematite Fe₂O₃ eventually reduced the magnetic properties of ferrites. The hematite, impurity phase, started to dissolve or converted into the ferrite phase after 600 °C. The sample annealed at 700 °C shows a better crystalline structure, phase formation, and larger magnetization compared to the other ferrite samples. The improved magnetic behavior after heat treatment is due to the better alignment of domains at the cost of the grain growth process. The UV-Vis spectroscopy result revealed the maximum absorbance at 380 nm.