PREPARATION AND CHARACTERIZATION OF SmCo<SUB>2</SUB> NANOCRYSTALLINE ALLOY WITH PERMANENT MAGNETIC PROPERTIES

The nanocrystalline SmCo2 bulk alloy with an average grain size of about 22 nm was prepared by combining high-energy ball milling and spark plasma sintering (SPS), in preparation the amorphous alloy powder obtained by milling was densified and crystallized during the SPS process. The microstructure, crystal structure and phase structure of such SmCo2 were determined. These results show that the nanocrystalline SmCo2 is not able to exist stably as a single phase at room temperature and decomposes into SmCo3 and Sm9Co4 phases, different from the conventional coarse- grained SmCo2 phase, which exists stably at room temperature. Phase stability and transformation behavior have been explained by the nanoscale thermodynamic simulation. Comparing with the coarse- grained SmCo2 with very weak magnetic properties, the nanocrystalline SmCo2 exhibits remarkable permanent magnetism and good overall magnetic properties.