Anisotropic Nd_2Fe_(14)B nanoparticles and nanoflakes by surfactant-assisted ball milling

摘要

Anisotropic Nd_2Fe_(14)B nanoparticles and nanoflakes have been produced by surfactant-assisted high-energy ball milling (SA-HEBM) of precursor nanocrystalline alloys. A two-stage high-energy ball milling was performed to obtain the nanopowders and nanoparticles; first the coarse powders were subjected to a wet milling followed by a wet surfactant-assisted milling. Different shaped nanoparticles have been obtained by varying the time of the first stage of the milling process and then separated by sonication. For a surfactant-free wet milling of 4 h, followed by the SA-HEBM, the nanopowders consisted of a mixture of Nd_2Fe_(14)B flakes with a thickness below 200 nm and an aspect ratio as high as 10~2-10~3, and anisotropic square nanoparticles with a size of 10 nm. However, for a shorter wet milling, nearly spherical nanoparticles with a size of 2.7 nm were obtained. Low-temperature coercivities have been obtained with maximum values of 4 kOe for square nanoparticles and 2.5 kOe for the nearly spherical nanoparticles.