Influence of the surfactant and annealing rate on the morphology, magnetic and structural characteristics of Co2FeAl nanoparticles

This research focuses on the synthesis and characterization of the attractive magnetic alloys, full-Heusler Co2FeAl nanoparticles. A modified co-precipitation method has been developed in a template of chitosan biopolymer. XRD pattern of the product confirmed the high crystalline quality of the L21‒ordered nanoparticles, refined by Rietveld analysis. It was found that using different annealing rates can be surprisingly effective to achieve different morphologies from granular microstructure to fibrous-shaped nanostructure. Based on the obtained results of the high resolution TEM image, the presence of both populations of large single crystal grains and polycrystalline clusters containing several small particles (about 10 nm) can be found in the sample annealed up to 700 °C with 5 °C/min. This particle size distribution led to the co-existence of high and low coercive-field phases in the related FORC diagram. Major hysteresis loops showed that the using of chitosan biopolymer resulted in a smaller magnetic saturation compared to that of the control sample, probably due to presence of the oxide shell around the surface of nanoparticles when exposed to air.