Low temperature hydrothermal synthesis of Ni_(75)Fe_(25) nanostructured powders: Microstructure, morphology and magnetic behaviour

摘要

We have successfully synthesised Ni75Fe25 nanostructured powders by means of low temperature (150 degrees C) hydrothermal method using sodium hydroxide (NaOH) as co-reduction agent. The powders are in fact large agglomerations of small nanoparticles with average diameters below 30 nm. The concentration of NaOH seems to play an important role in the final microstructure and morphology of the samples as deduced from scanning electron microscopy images. Although x-ray diffraction patterns reveal that the samples are single-phase with a face centered cubic crystal structure, the analysis of Mossbauer spectra suggests the existence of different local environments for the iron atoms. The room temperature saturation magnetization shows similar values for all the samples ( approximate to 90 Am-2/kg), in contrast with the coercive field that is clearly influenced by the morphology of the samples, ranging from 60 Oe (spherical-shaped samples) to 150 Oe (denditric-shaped powders).