Evolution of Nd2Fe14B nanoparticles magnetism during surfactant-assisted ball-milling

The aim of this work was the fabrication of Nd2Fe14B nanoparticles, through a “top-down” technique like surfactant-assisted high-energy ball-milling, and the monitoring of the milling-process stages with respect to the structure and magnetism. The ball-milling of a 40 μm powder under Ar atmosphere, in an organic solution of oleic acid/oleylamine, resulted in 15 nm isolated nanoparticles after 20 h, presenting improved magnetocrystalline anisotropy compared to the initial material. By extending the mechanical process up to 100 h a gradual formation of elongated nanoparticles followed by structural amorphization was observed.

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► Monitoring of surfactant-assisted ball-milling process for Nd2Fe14B nanoparticles.
► Milling time and surfactants determine the size, shape, structure and magnetism.
► Optimum energy product is achieved in the size range 50–100 nm.
► Particles are isolated at sizes lower than 20 nm after 15 h of milling.
► Further treatment affects the shape and the crystallinity.