Structural stability and magnetic properties of metastable Fe-Cu alloys studied byab initiocalculations and molecular dynamics simulations

For the equilibrium immiscible Fe-Cu system, ab initio calculations using the projector augmented wave method identify the relatively stable structures of the metastable Fe₂₅Cu₇₅ and Fe₅₀Cu₅₀ alloys to be both of fcc and determine their corresponding lattice constants and cohesive energies. Some of the ab initio calculated properties are used in deriving an embedded-atom Fe-Cu potential. Based on the proven realistic potential, the structural stability of the FeₓCu_100-x alloy is studied for the entire composition range of the system through molecular dynamics simulations. The simulations predict that a fcc structure is more stable than a bcc one when $0<~x<~60,$ while the bcc structure becomes energetically favored when $60<x<~100,$ and that the prediction confirms the verdict from ab initio calculations for the Fe₂₅Cu₇₅, Fe₅₀Cu₅₀, and Fe₇₅Cu₂₅ alloys. Moreover, ab initio calculations are also performed to determine the magnetic moments of some metastable Fe-Cu alloys and the results are reasonably compatible with the experimental observations.