Formation of SmCo 5 single-crystal submicron flakes and textured polycrystalline nanoflakes

Abstract

Surfactant-assisted high-energy ball milling (HEBM) of malleable materials has been found to lead to the formation of flakes. However, SmCo 5 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 SmCo 5 by one-step surfactant-assisted HEBM in heptane with 15 wt.% oleic acid. Single-crystal micron flakes were first formed via a basal cleavage along the easy glide (0 0 1) 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 SmCo 5 nanoflakes were formed with [0 0 1]-out-of-plane texture, thicknesses of 6–80 nm, average grain sizes of 7–8 nm, an aspect ratio of 10 2–10 3 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.