FePt and CoPt nanoparticles co-deposited on silicon dioxide-a comparative study

Area of Science:

• Materials Science
• Nanotechnology
• Magnetism

Background:

• Nanoparticles offer unique magnetic properties due to their size.
• Ordered intermetallic phases, like L1(0), are crucial for high-performance magnetic materials.
• Controlling phase transitions in nanoparticles is key for advanced applications.

Purpose of the Study:

• To compare the growth and magnetic hardening of CoPt and FePt nanoparticles.
• To investigate the role of annealing in forming the L1(0) phase in these nanoparticles.
• To determine the coercivity differences between annealed CoPt and FePt nanoparticles.

Main Methods:

• CoPt and FePt nanoparticles were synthesized via electron beam co-evaporation on oxidized Si substrates.
• High vacuum conditions and a substrate temperature of 1023 K were employed during growth.
• Samples underwent an immediate post-growth annealing step to induce phase transformation and magnetic hardening.

Main Results:

• Nanoparticles with mean diameters of 17-22 nm were formed.
• Annealing led to grain size enlargement and significant magnetic hardening in both CoPt and FePt.
• Maximum perpendicular coercivities reached ~6.6 kOe for CoPt and ~10.2 kOe for FePt nanoparticles.
• A progressive transition to the L1(0) ordered phase was observed in both materials during annealing.

Conclusions:

• Annealing is essential for CoPt nanoparticles to crystallize into the hard magnetic L1(0) phase.
• FePt nanoparticles also transition to the L1(0) phase upon annealing, exhibiting higher coercivity than CoPt.
• The study highlights the importance of post-growth annealing for optimizing magnetic properties of CoPt and FePt nanoparticles.