Low-temperature FCC to L1 phase transformation in CoPt(Bi) nanoparticles

This work is focused on the effects of Bi substitution on the synthesis of CoPt nanoparticles with the L10 structure using a modified organometallic approach. The structural and magnetic properties of the nanoparticles have been studied and compared directly with those of CoPt nanoparticles synthesized by the same technique but in the absence of Bi substitution. The as-synthesized particles at 330 °C have an average size of 11.7 nm and a partially ordered L10 phase with a coercivity of 1 kOe. The coercivity is increased to 9.3 kOe and 12.4 kOe after annealing for 1 hour at 600 and 700 °C. The structural and magnetic properties suggest that Bi promotes the formation of ordered L10 phase at low temperatures leading to the development of high coercivities.