A comparative study on the effects of different milling atmospheres and sintering temperatures on the synthesis and magnetic behavior of spinel single phase Ni_0.64Zn_0.36Fe₂O₄ nanocrystals

Abstract

Synthesis of Ni_0.64Zn_0.36Fe₂O₄ ferrite nanoparticles via mechanical alloying and subsequent heat treatment was investigated. The pure metal powder of Zn, Fe₂O₃ and NiO were ball milled in three different atmospheres including argon, oxygen and air. The X-ray diffraction results showed that after a long time of 30 h milling a desired ferrite was not produced, but heating the 30 h-activated powders in as low a temperature as 400 °C for 2 h led to the formation of Ni–Zn ferrite nanocrystals with some residual Fe₂O₃ phase. The particle size and lattice parameter of the Ni–Zn ferrite samples were strongly affected by the milling atmospheres. TEM results indicated that the average particle size of the milled samples in the argon atmosphere was the smallest and in the range of 5–67 nm. FT-IR spectra for the Ni–Zn ferrite samples showed two absorption bands associated with tetrahedral and octahedral sites around 600 and 400 cm⁻¹, which depend on the milling atmosphere; their wave-number positions were different. The VSM results indicated that the magnetic properties i.g. M_s were not only affected by the milling atmosphere but also by the sintering temperature. Although increasing sintering temperature caused an increase of the M_s value in all the three atmosphere-milled samples, the milled-sintered samples in the argon atmosphere had the biggest M_s value about 96 emu/g after sintering at 1000 °C.