Polycrystalline Nd2Fe14B/α-Fe nanocomposite flakes with a sub-micro/nanometre thickness prepared by surfactant-assisted high-energy ball milling

A surfactant-assisted high-energy ball milling technique was employed to synthesize Nd2Fe14B/α-Fe nanoparticles and nanoflakes from melt-spun nanocrystalline powders. The microstructure evolution in ball milling process was investigated. In the beginning stage (0-4 h) of ball milling, raw powders were crushed into micrometre-sized particles. While flakes were mainly formed by reducing thickness of particles via peeling layer by layer along preferential planes in the late stage (8-16 h). The selected area electron diffraction and high-resolution transmission electron microscopy images show that preferential cleavage planes are basal planes. With ball milling proceeding, more and more defects were induced by ball milling. As a result, the coercivity and remanence decreased to 1.6 kOe and 3.2 kGs, respectively. After 16 h ball milling, the exchange decoupling occurred due to severe amorphorization. A weakly-textured nanocomposite magnet was fabricated after 12 h ball milling and the anisotropy in magnetic properties can be further improved by employing settling down process to select particle size and aligning particles in external field.