Effect of different surfactants on the formation and morphology of SmCo5 nanoflakes Original Research Article

The effect of the amount and types of surfactants and milling time on the formation of SmCo5 nanoflakes by surfactant-assisted high-energy ball milling in heptane has been investigated. The majority of the as-milled SmCo5 samples had the shape of flakes with a high degree of texture. Among the surfactants used, oleylamine (OY), trioctylamine (TOA) and oleic acid (OA), OA and OY have similar effects on the formation of SmCo5 nanoflakes, with the highest coercivity of 20.1 kOe obtained after 5 h of milling with 2 wt.% OA. Textured poly-nanocrystalline SmCo5 nanoflakes were formed even with as little as 2 wt.% OA. The coercivity of the specimens prepared with 2–10 wt.% of OA increased from 10.8 to 20.1 kOe when the milling time increased from 0.25 to 5 h. However, the same amount of OA had little effect on the coercivity and grain size when the milling time was kept for 5 h. In the case of TOA, a higher amount of surfactant is required to form the nanoflakes. The evolution of thickness, structure and magnetic properties of SmCo5 flakes with increasing milling time has a similar trend with all surfactants used. The [0 0 1] texture was found to be reduced either with decreasing the amounts of OA from 10 to 2 wt.% when the milling time was 5 h or with increasing the milling time from 0.25 to 5 h when the amount of OA was kept at 5 wt.%. Another interesting result is that the majority of jet-milled SmCo5 powders became more uniform and had a smaller size in the range of 0.3–3 μm when using milling balls with a single diameter of 4 mm. The small size and uniform nanoflakes are very promising for the development of anisotropic nanocomposite magnets.