Multiply twinned morphologies of FePt and CoPt nanoparticles

Area of Science:

• Computational materials science
• Condensed matter physics
• Surface science

Background:

• Iron-platinum (FePt) and cobalt-platinum (CoPt) alloys are crucial for magnetic storage media due to their high magnetocrystalline anisotropy.
• Understanding the size-dependent properties of nanoscale clusters is essential for designing advanced magnetic materials.
• The energetic order and magnetic characteristics of different cluster morphologies significantly influence their performance.

Purpose of the Study:

• To systematically investigate the size dependence of energetic order and magnetic properties for FePt and CoPt clusters.
• To compare the stability of various cluster morphologies, including multiply twinned structures and the L1_(0) phase.
• To elucidate the electronic origins of compositional trends in these bimetallic clusters.

Main Methods:

• Large-scale density functional theory (DFT) calculations were employed.
• Simulations covered FePt and CoPt clusters with diameters up to 2.5 nm.
• Analysis focused on energetic stability and magnetic properties across different morphologies.

Main Results:

• For FePt clusters, ordered multiply twinned icosahedra and decahedra were found to be more energetically favorable than the L1_(0) phase across all investigated sizes.
• CoPt clusters predominantly exhibited segregated morphologies, with significantly larger energy differences compared to the L1_(0) structure.
• Compositional trends were correlated with differences in the partial electronic density of states of the 3d elements within various morphologies.

Conclusions:

• Multiply twinned structures are energetically preferred for FePt clusters at the nanoscale.
• Segregated morphologies are dominant for CoPt clusters, indicating a different stability landscape compared to FePt.
• The electronic structure of 3d elements plays a key role in determining the stability and properties of these bimetallic clusters.