Formation of SmCo5 single-crystal submicron flakes and textured polycrystalline nanoflakes

Surfactant-assisted high-energy ball milling (HEBM) of malleable materials has been found to lead to the formation of flakes. However, SmCo5 magnetic materials are inherently brittle and, therefore, are not expected to "flake" during ball milling. In this study, we report the fabrication of high-aspect-ratio single-crystal flakes with a submicron thickness and textured polynanocrystalline flakes with a submicron or nanosize thickness of SmCo5 by one-step surfactant-assisted HEBM in heptane with 15wt.% oleic acid. Single-crystal micron flakes were first formed via a basal cleavage along the easy glide (001) planes of the initial irregular and large single-crystal particles during the first stage of HEBM. Subsequently, single-crystal submicron flakes were formed by continuous cleavage. With further ball milling, polycrystalline submicron flakes with small-angle grain boundaries were formed. Finally, crystallographically anisotropic polycrystalline SmCo5 nanoflakes were formed with [001]-out-of-plane texture, thicknesses of 6-80nm, average grain sizes of 7-8nm, an aspect ratio of 102-103 and coercivities of 16.3-17.7 kOe. The mechanism responsible for unusual formation of single-crystal submicron flakes and anisotropic nanocrystalline nanoflakes from initial inherently brittle polycrystalline ingots with irregular grains of tens of microns in size is discussed.