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

The SrFe/sub 12/O/sub 19/ powders prepared by a sol-gel method were annealed at temperatures ranging from 400(degree)C to 900(degree)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(degree)C by XRD. In the sample annealed at 800(degree)C, lattice constants are a/sub 0/=5.9227 A c/sub 0/=23.2368 A and particle size was about 74 nm. The coercivity of the samples increased from 6.2 Oe for the powder annealed at 500(degree)C to 7000 Oe for annealed powder at 800(degree)C. The saturation magnetization increased from 30.7 emu/g to 63.0 emu/g as annealing temperature is increased from 500(degree)C to 800(degree)C.