The physical properties of iron-rich Fe-Co alloys: Analysis from the perspective of Co concentration

Abstract

Although the ground-state structure and magnetism of Fe-Co alloys are well known, the physical properties such as lattice dynamics, elasticity, and magnetocrystalline anisotropy are rarely reported. Here, the physical properties of Fe_16-xCo_x (x = 1–8) alloys are systematically investigated using first-principles calculations, with emphasis on the composition-property relationship. As Co concentration increases, the lattice volume, total magnetic moments (saturation magnetization), and first magnetocrystalline anisotropy constants of the alloys initially increase and subsequently decrease, with Fe₁₃Co₃ alloy exhibiting an extremum. The dynamical and mechanical properties change with Co concentration in non-specific trends. Most alloys are both mechanically and dynamically stable. The Fe₁₂Co₄ and Fe₉Co₇ are dynamically and mechanically unstable, respectively. The elastic modulus, ductility/brittleness, and elastic anisotropy are explored in detail. Finally, the magnetic hardness parameters show that Fe₁₃Co₃ alloy is a semi-hard magnet, while other alloys are soft magnetic materials. This research provides a theoretical basis for the application of Fe-Co alloys.