Rare earth–cobalt hard magnetic nanoparticles and nanoflakes by high-energy milling

Abstract

High-energy ball milling has been shown to be a promising method for large-scale fabrication of rare earth-transition metal nanoparticles. In this work, we report crystallographically anisotropic SmCo(5), PrCo(5) and Sm(2)(Co, Fe)(17) nanoparticles (particle size smaller than 10 nm) obtained by surfactant-assisted ball milling and study their size and properties as a function of the milling conditions. By milling nanocrystalline precursor alloys, we obtained SmCo(5) platelets (flakes) approximately 100 nm thick with an aspect ratio as high as 10(2)-10(3). The unusual shape evolution of this brittle material is attributed to its increased plasticity in the nanocrystalline state. The nanoflakes are susceptible to re-crystallization annealing and exhibit a room-temperature coercivity of up to 19 kOe. The successful fabrication of rare earth-cobalt nanoparticles and ultra-thin flakes provides hope for the development of nanocomposite permanent magnets with an enhanced energy product.

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

“…Finally, textured polynanocrystalline SmCo 5 nanoflakes are formed. It should be mentioned that the continuous decrease in thickness of the polynanocrystalline nanoflakes during the HEBM is believed to be mainly due to the significant ductility exhibited by brittle materials in a nanocrystalline state [22] rather than the basal cleavage of the easy glide (0 0 1) planes which dominates in the stage of formation of single-crystal micron and submicron flakes.…”

Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl

“…Sintered Nd 2 Fe 14 B is easily subjected to grain boundary corrosion and the polymer-bonded Nd 2 Fe 14 B magnets have a significantly lower energy. Sm-Co magnets on the other hand are quite brittle and can fracture from thermal shock [4]. Other RE-free magnets are more commonly used, but these magnets generally have lower coercivity, H C .…”

Generation and Characterization of Anisotropic Microstructures in Rare Earth-Iron-Boron Alloys

“…A more recent method of inducing texture through a process known as surfactant-assisted ball milling has been attempted by several groups [49][50][51][52][53]. In this process, isotropic (or large-grained) particulate, milling balls, and an organic surfactant (often oleic acid) is placed within a ball mill jar and high energy ball-milled.…”