Chemical ordering phenomena in nanostructured FePt: Monte Carlo simulations.

Area of Science:

• Materials Science
• Computational Materials Science
• Nanotechnology

Background:

• FePt alloys exhibit the L10 superstructure, crucial for high-density magnetic recording media.
• Surface effects significantly influence the ordering behavior of nanomaterials.
• Understanding nanoscale ordering is key to developing advanced magnetic materials.

Purpose of the Study:

• To investigate free-surface-induced L10 chemical long-range ordering in FePt nanostructures (nanolayer, nanowire, nanoparticle).
• To model and quantify the nucleation and stability of L10 variants under different dimensionalities.
• To elucidate the role of surfaces in initiating chemical ordering.

Main Methods:

• Monte Carlo simulations using interatomic pair interactions derived from ab initio calculations.
• Modeling of vacancy-mediated atomic migration via the Glauber algorithm below the order-disorder transition temperature.
• Development of a parameterization to quantify volume fractions of specific L10 variants.

Main Results:

• Observed (100)-type surface-induced heterogeneous nucleation of L10-order domains across all studied nanostructures.
• Identified the c-L10 variant as the most stable in cubic nanoparticles due to surface interactions.
• Demonstrated that chemical ordering initiates at free surfaces, leading to surface domain structures and bulk ordering.

Conclusions:

• Free surfaces play a critical role in initiating and stabilizing L10 chemical ordering in FePt nanostructures.
• Nanostructure dimensionality and surface characteristics dictate the preferred L10 variant and overall ordering stability.
• The findings provide insights into the design and fabrication of FePt-based nanomagnetic materials.