Ab Initio Studies of Segregation, Ordering, and Magnetic Behavior in (Fe–Pt)_n, n = 55 and 147: Design of Fe₇₅Pt₇₂ Nanoparticle

Abstract

We report results of a systematic study on atomic and electronic structure of 55-atom and 147-atom Fe−Pt nanoparticles with different compositions using ab initio calculations. Our results on 55-atom nanoparticles suggest icosahedral structure and segregation of Pt on the surface to be favorable. Also, there is a tendency for Fe−Pt ordering on the surface and maximization of the unlike bonds similar to the bulk, while the core is made of pure Fe 13 , giving it a core−shell structure. Using these considerations, we designed a unique 147-atom icosahedral Fe 75 Pt 72 nanoparticle in which a 55-atom core is made of Fe atoms and 72 Pt atoms are on the outer shell of the icosahedron. Twenty Fe atoms are on the centers of the Pt hexagons on the faces of the icosahedron. This nanoparticle has 260 μ B magnetic moments, and the local magnetic moments on Fe and Pt atoms are higher compared with the values in bulk FePt. The free Fe 55 cluster has a distorted icosahedral structure to be most favorable, with large magnetic moments (∼3 μ B /atom), which we also find in the core of the nanoalloy particle, but the surface Fe atoms have higher magnetic moments of about 3.4 μ B /atom. All the Pt atoms are on the surface with Fe−Pt ordering in a nearly symmetric icosahedral structure, and the heat of formation is the highest, which makes it an optimal nanoparticle. The overall composition of this nanoparticle is FePt-like, but it decomposes to Fe core and Fe−Pt shell.

Ab Initio Insights into the Formation Mechanisms of 55-Atom Pt-Based Core–Shell Nanoalloys

“…The core–shell arrangement can start with small nanoclusters; for example, it has been shown that various compositions of PtCu nanoalloys of up to 14 atoms resemble core–shell structures, which are favorable due to the strain released by allocating the smaller atom on the core region . Furthermore, the stability trends related to the preference of certain elements for the surface or core regions can hold for a range of compositions, for example, PtFe nanoalloys are generally more stable with all or most Pt atoms on the surface region. − …”

A perspective on the controlled synthesis of iron-based nanoalloys for the oxygen reduction reaction

“…The effects of nanoalloy particle size, physical phase, and other parameters on the FePt nanoalloys structure and properties have also been investigated with simulation methods. [44][45][46] For example, an embedded atom model with a classical molecular dynamics simulation method has been applied to study the size of 2-6 nm and temperature of 300-2700 K on the FePt nanoalloys' stability and local structural evolutions. 47 The simulation results reveal that the most stable atomic configurations are the deformed bcc and deformed icosahedron structures regardless of the liquid state at 1700 K or the glassy state at 300 K. As for the structure revolution, the phase separation at about 300 K and at the nano scale would result in the core-shell structure with Fe-rich shell and Pt-Fe-rich core, which means the FePt nanoalloys are core-shell structures instead of homogenous element distribution.…”

Co₁₃Cu₈₇ and Fe₃O₄ Nanoalloys for Ultrahigh Density Magnetic Storage

“…This leads to the conclusion that nanoparticle-containing devices have a lot of potential for storing data. 2 On inspecting the properties of Fe, Pt, Co, Cu, etc, it can be understood that the magnetic properties of FeO and CuCo nanoalloys suit the best for this purpose.…”