The annealing temperature dependence of magnetic properties in Sr-ferrite nanoparticles

The SrFe₁₂O₁₉ powders prepared by a sol-gel method were annealed at temperatures ranging from 400°C to 900°C for 3 h and 6 h in air. Magnetic and structural properties of the powders were characterized with a vibrating sample magnetometer (VSM), X-ray diffractometer (XRD), scanning electron spectroscopy (SEM), Mossbauer spectroscopy, thermogravimetry (TG), and differential thermal analysis (DTA). M-type hexagonal phase is observed in the samples annealed at temperatures above 600°C by XRD. In the sample annealed at 800°C, lattice constants are a₀=5.9227 Å c₀=23.2368 Å and particle size was about 74 nm. The coercivity of the samples increased from 6.2 Oe for the powder annealed at 500°C to 7000 Oe for annealed powder at 800°C. The saturation magnetization increased from 30.7 emu/g to 63.0 emu/g as annealing temperature is increased from 500°C to 800°C.