Spectroscopy studies of NIFe_2O_4 nanosized powders obtained using coconut water

摘要

High-quality NiFe_2O_4 nanosized powders were prepared by a new route using a natural proteic solution of coconut water and metal ions. The transition from the superparamagnetic to the ferrimagnetic state was observed with the increase of the heat-treatment temperature from 400 deg C to 800 deg C. In this work, Electron Paramagnetic Resonance (EPR), a.c. magnetic susceptibility (Xa.c.) measurements, infrared (FT-IR) and Raman spectroscopy have been employed to obtain additional information about the structural evolution of the NiFe_2O_4 nanoparticles, with the increase of the heat-treatment temperature. The obtained results show that the heat-treatment temperature makes remarkable changes in the structure of the samples. The NiFe_2O_4 nanocrystallite samples, treated at 1200 deg C, exhibit a large a.c. magnetic susceptibility which was related with the formation of a mixed spinel phase. This is in agreement with the Mossbauer spectroscopy results. The increase of the volume of the nickel ferrite leads to an increase of the magnetic susceptibility. The magnetic properties of these nanoparticles are clearly size dependent.