A FORC investigation into the effect of Cu additive on magnetic characteristics of Co-Ni alloy nanoparticles

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−xCu_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 CoNi₁₀Cu₄₀. 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.