High coercivity SmCo₅ synthesized with assistance of colloidal SiO₂

SmCo₅ is one of the most promising candidates for achieving a hard magnet with a high coercivity. Usually, composition, morphology, and size determine the coercivity of a magnet, however, it is challenging to synthesize phase pure SmCo₅ with optimal size and high coercivity. In this paper, we report on the successful synthesis of phase pure SmCo₅ with spherical/prolate spheroids shape. Size control is obtained by utilizing colloidal SiO₂ as a template preventing aggregation and growth of the precursor. The amount of SiO₂ nanoparticles (NPs) in the precursor tunes the average particle size (APS) of the synthesized SmCo₅ with particle dimension from 740 to 504 nm. As-prepared pure SmCo₅ fine powder obtained from using 2 ml SiO₂ suspension possesses an APS of 625 nm and exhibits an excellent coercivity of 2986 kA m^-1 (37.5 kOe) without alignment of the particles prior to magnetisation measurements. Comparing with a reference sample prepared without adding any SiO₂ NPs, an enhancement of 35% of the coercivity was achieved. The improvement is due to phase purity, stable single-domain (SSD) size, and shape anisotropy originating from the prolate spheroid particles.