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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 coexistence 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.

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Magnetic hollow nanoparticles (HNPs) are of particular interest owing to their broad applications including targeted drug delivery and magnetic resonance imaging. Here, hollow Co2FeAl full-Heusler NPs were successfully synthesized using polyethylene glycol polymer as a capping agent, followed by thermal annealing at 700 °C with heating rates ranging between 5 and 15 °C/min. Increasing heating rate up to 15 °C/min decreased the mean particle size, as characterized by scanning and transmission electron microscopies (TEM). High resolution TEM images revealed the highly crystalline nature of the HNPs with different grain size. A maximum saturation magnetization of 95 emu/g and coercivity of 730 Oe were obtained using heating rates of 5 and 10 °C/min, respectively. Alternatively, first-order reversal curve (FORC) measurements at room temperature revealed the formation of a mixture of single-domain and superparamagnetic (SP) grains due to the presence of a wide range of particle size. With the increase in the heating rate, the SP contribution increased, which resulted in a decrease in the inter-particle magnetostatic interactions, thereby approaching the average coercivity obtained from hysteresis curve to FORC coercivity.

Nanoparticles of Co 2 FeAl magnetic alloy was successfully fabricated in the presence of a well-known capping agent, polyvinyl alcohol, as a polymer template. The magnetic properties were studied using hysteresis curve and firstorder reversal curve (FORC) measurements at room temperature. FORC diagrams demonstrated a wide distribution of the coercive field owing to the presence of different particle sizes in products. TEM image also showed that the synthesized samples are composed of some large clusters containing a few smaller particles. The maximum value of magnetization (*76 emu/g) and coercivity (573 Oe) were obtained in the annealed sample with 5°C/min. A wider distribution of grain size with a smaller average of 20.5 nm as well as lower-degree of crystallinity was observed in the sample annealed with higher rate of 10°C/min.