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

Abstract

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 °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 °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 °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 °C due to a reduction in density of lattice imperfections and strain.