Effect of milling parameters on SmCo₅ nanoflakes prepared by surfactant-assisted high energy ball milling

In this study, we discuss the effect of different milling parameters, such as the type and concentration of surfactants, milling energy, and milling time on the structural, morphological and magnetic properties of hard magnetic SmCo₅ nanoflakes prepared by surfactant assisted high energy ball milling. Two kinds of surfactants, polyvinylpyrolidone (PVP) with ethanol and oleic acid (OA) with n-heptane, were used as milling media. Increase in surfactants concentration and decrease in milling energy result in the decrease of degree of amorphization and reduction in grain size with milling time. Milling at 200 rpm results in more homogeneous and thicker flakes with fewer fractions of nanoparticles as compared to milling at 800 rpm. Increase in surfactants concentration results in the increase of the aspect ratio of flakes. Due to better capping ability of OA, the degree of flaking is higher when milling in OA than that in case of PVP. A maximum coercivity of 2.3 T was obtained after milling for 1.0 and 2.0 h for 10 and 50 wt. % of OA, respectively, at 800 rpm. A maximum (BH)_max of 23.8 MGOe (188.9 kJ m⁻³) and degree of texture of 93% were obtained for 10 wt. % OA after 10 h of milling at 200 rpm. The pronounced anisotropy and high coercivity of the nanoflakes should prove advantageous for the preparation of textured exchange spring magnets.