Magnetic properties of interacting CoPt nanoparticles synthesized through polyol process

Co₄₀Pt₆₀ nanoparticles with an average particle size of 3.9 nm were prepared by polyol pathway without incorporating any capping agents or surfactants. The as-prepared nanoparticles were superparamagnetic having disordered A1-face centered cubic structure, which transforms to face centered tetragonal (L1₀) phase on heat treatment, without the requirement of a reducing gas. The Curie temperature of the Co₄₀Pt₆₀ nanoparticles was determined to be 482 °C from the thermomagnetic analysis. Coercivity upto 7 kOe was obtained on annealing at a relatively lower temperature of 600 °C. Anomalous variation in coercivity has been observed with annealing. Annealing temperature dependent two phase behavior was studied by δM measurements. The CoPt samples exhibited dipolar coupling on annealing up to 700 °C and strong exchange coupling was evident with further increase in annealing temperature. - Highlights: • A simplified one-step one-pot polyol process to synthesis CoPt nanoparticles. • Coercivity upto 7 kOe obtained on annealing at a relatively lower temperature of 600 °C. • Curie temperature determined by thermo-magnetic analysis. • Inter-particle interactions studied by δM analysis