Mechanism of grain size refinement of Fe3B/Nd2Fe14B nanocomposite permanent magnet by Cu addition

Minor addition of Cu to Nd4.5Fe77B18.5 melt-spun alloy is effective on redu cing the grain size of the Fe3B/Nd2Fe14B nanocomposite permanent magnet pro duced via the crystallization route from the amorphous phase, thereby impro ving hard magnetic properties. Three-dimensional atom probe and transmissio n electron microscopy observations have shown that Cu clusters with a numbe r density of similar to 10(24) m(-3) is formed prior to the nucleation even t of the Fe3B primary crystal. In the nucleation and growth stage of the Fe 3B primary crystals, Cu clusters are in direct contact with the primary par ticles, suggesting that Cu clusters serve as heterogeneous nucleation sites for the Fe3B primary particles, thereby increasing the number density of t he particles. (C) 1999 American Institute of Physics. [S0021-8979(99)03504- 5].