Ferromagnetic L1₀-Structured CoPt Nanoparticles for Permanent Magnets and Low Pt-Based Catalysts

CoPt nanoparticles were successfully synthesized following a one-step liquid-phase chemical approach in the presence of a bismuth additive. The presence of bismuth enhanced the structural ordering, the particle morphology, and suppressed the sintering of nanoparticles during the postannealing. The effect of bismuth addition was studied extensively, and the synthesized nanoparticles were characterized by a plethora of techniques determining their crystal structure, particle size and morphology, while the magnetic properties were measured by vibrating sample magnetometry. The CoPt nanoparticles even in the as-made state reveal a relatively high room-temperature coercivity, up to 1.7 kOe, while after thermal annealing at 700 °C for 1 h, the coercivity reaches ∼14.6 kOe; these values are among the highest observed for CoPt nanoparticles. Furthermore, the excess bismuth phases could be removed by a simple acid treatment, leaving the structure and magnetic properties nearly unchanged for the annealed nanoparticles. These L1₀-structured CoPt nanoparticles have potential applications in the fields of permanent magnets as well as low Pt-based catalysts.