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Half-Heusler nanostructures of CoFeAl alloys, synthesized via coprecipitation route, were found to contain both hard- and soft-phases magnetic grains, mapped using first-order reversal curves (FORCs) diagrams. The obtained results confirmed that these powders are highly interacting as a single-domain magnetizing system. A significant dependence of the morphology and particle size on the annealing rate was represented by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM images. The presence of the strong magnetizing interaction between the nanoparticles led to the formation of chain-like structure stabilized by PVP polymer. By increasing the annealing rate from 278.15 K/min to 288.15 K/min (5 °C/min to 15 °C/min), the grain shape changed from long nanochain to nonuniform agglomerated grains. Additionally, the magnetic characteristics of the prepared alloys were found to be affected by tuning the annealing rate. [ABSTRACT FROM AUTHOR]

A systematic study of the size effect on the structural and magnetic properties of CoFeAl ternary alloys with different particle sizes has been performed in this work. The average particle size was controlled in a range from a few nanometers to micrometers by tuning the annealing rate. Upon annealing process at 700 °C in the presence of the surfactant matrix of CTAB, the B2-ordered structures with an average particle size of 35 nm were obtained under heating rate of 15 °C/min. Decreasing the reaction rate provided a well-arranged crystallization, leading to an enhanced saturation magnetization as well. For studying the effect of surfactant, samples were also synthesized in the absence of CTAB. A higher agglomeration is clearly observed in these samples compared to the previous ones, and the particle size was found to be significantly affected by the presence of surfactant, in spite of the magnetization. First-order reversal curve analysis revealed the presence of low- and high-coercive field particles in both samples, indicating that the products were composed of an assembly of particles with different sizes. By isolating the reversible and irreversible components of the magnetization, it was found that the behavior of the prepared samples is reversible (more than 59 %) as the percentage of the reversibility increased with decreasing the average particle size. [ABSTRACT FROM AUTHOR]

Highlights • Using a cost-effective polyol method, CoNi binary alloy nanoparticles were synthesized. • Effect of Cu additive on morphology, structure and magnetic properties was investigated. • The FORC analysis was employed to study the magnetic characteristics in details. • Increasing the Cu content increased the separation between soft and hard phases. • The magnetic interaction between particles was reduced when increasing the Cu content. Abstract CoNi binary alloy nanoparticles were prepared by using a polyol method. The effect of the Cu additive (acting as the third element) on structural and magnetic properties of the CoNi 50−x Cu x (10 ≤ x ≤ 40) alloy was then studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), magnetometry and first-order reversal curve (FORC) analyses. It was found that a combination of Co-Ni alloy and Cu phases is formed when increasing the Cu content by x = 10 and 20. However, for x = 30 and 40, the resulting compound is obtained in the form of a single-phase ternary alloy. Increasing the Cu content increases the separation between soft and hard phases in the FORC diagram, leading to two distinct magnetic phases in CoNi 10 Cu 40. The FORC data showed that the magnetic interaction between particles was reduced when increasing the Cu content. The reversible and irreversible components of the compounds were also estimated. The FESEM images showed the formation of ordered spherical CoNi alloy grains with a diameter of about 400 nm, comprising tight nanoparticles with sizes below 100 nm. Moreover, in the presence of the element Cu, a variation in the nanoparticle size and morphology was seen clearly. [ABSTRACT FROM AUTHOR]