The role of magnetism in the formation of the two-phase miscibility gap in β Cu–Al–Mn

A theoretical study of the ground state properties of alloys with compositions along the pseudobinary line Cu₃Al–Cu₂AlMn is presented. Cohesive energies, lattice parameters and magnetic moments of the two limiting compounds and three intermediate compositions are calculated by means of density functional theory. In order to evaluate the role of magnetism, both the spin-polarized (SP) and the non spin-polarized (NSP) cases have been considered. It is shown that magnetism plays a central role on the stabilization of the L2₁ crystal structure in Cu₂AlMn, and in the formation of the miscibility gap in Cu₃Al–Cu₂AlMn. The considerable lattice mismatch between the end compounds can be attributed also to magnetic effects. - Highlights: • Alloys with compositions Cu_3−xAlMn_x were studied by first principles methods. • Both spin-polarized (SP) and non-spin-polarized (NSP) calculations were done. • Cohesive energies, lattice parameters and magnetic moments were determined. • The phase separation Cu₃Al+Cu₂AlMn is attributable to magnetic effects. • In the NSP case, L2₁ Cu₂AlMn is predicted to be unstable against the F43m structure