Structure and magnetic properties of Ni0.64Zn0.36Fe2O4 nanoparticles synthesized by high-energy milling and subsequent heat treatment

High energy ball milling and subsequent annealing were applied to synthesize nanocrystalline Ni0.64Zn0.36Fe2O4 ferrite from a powder mixture of pure metal Zn, Fe2O3 and NiO in an oxygen atmosphere. The structural and phase evolution of powder particles after different milling times were studied by X-ray diffractometry. The XRD results showed that a Ni-Zn ferrite was formed with some residual Fe2O3 by annealing a 30-h-milled sample at as low as 400 degrees C for 2 h. The average crystallite size of the 30 h-milled powder was estimated to be about 15 nm which grew to 21 nm after annealing at 500 degrees C for 2 h. TEM image showed an agglomerated state of particles for 30 h-milled powders. FT-IR analysis indicated two absorption bands in the Ni-Zn ferrite structure related to octahedral and tetrahedral sites, respectively, in the range of 400-600 cm(-1). Thermogravimetric analysis showed a mass loss about 2 % for as-received powder mixture below 400 degrees C; after that, it was almost stable. The Ni-Zn ferrite formation mechanism was detected to be in three stages: oxidation of zinc, diffusion of ZnO in Fe2O3 and the formation of ZnFe2O4, and diffusion of NiO in ZnFe2O4 and the formation of Ni-Zn ferrite. Vibrating sample magnetometery results revealed that a saturation magnetization of the 30 h-milled sample was about 5 emu/g which increased to 16 emu/g after annealing at 400 degrees C due to a reduction in density of lattice imperfections and strain.