Anisotropic SmCo₅ flakes and nanocrystalline particles by high energy ball milling

This work is focused on the evolution of structure, texture and magnetic properties in SmCo₅ powders during high energy ball milling (HEBM) in heptane with and without oleic acid (OA). Single-crystal micron SmCo₅ flakes were formed in the early stage of HEBM (0–0.5 h). However, HEBM of 1–2 h without OA led to the formation of a mixture of single-crystal microflakes and loosely agglomerated polycrystalline microparticles with the highest coercivity of 15.7 kOe. HEBM of 3–5 h without OA led to the formation of isotropic, more or less equiaxed SmCo₅ particles with a size of 2–30 μm and a polycrystalline nanostructure due to the coalescence of flakes and particles. In the case of HEBM in heptane with 15 wt. % OA, prolonged milling (from 1 to 5 h) led first to the formation of SmCo₅ single-crystal submicron flakes and later to submicron- and nanosize-nanocrystalline flakes with a [001]-out-of-plane texture. OA plays an essential role in the formation of anisotropic SmCo₅ flakes via the impediment of cold welding and agglomeration of flakes. The highest coercivity of 17.7 kOe was obtained in a flake sample milled for 5 h with a thickness of 8–80 nm, an average grain size of 8 nm and an aspect ratio of 10²–10³.