Effect of magnetism on lattice dynamical properties in the Ni–Cu alloy from first principles

Abstract

We have studied the lattice dynamical properties of the magnetic intermetallic Ni1−xCux alloy within the framework of density functional perturbation theory using a mixed-basis pseudopotential method and the self-consistent virtual crystal approximation for modeling the alloy. A transition from a ferromagnetic (FM) to a non-magnetic (NM) state is found at a critical concentration xc=0.45. Phonon spectra as a function of x for both FM and NM states obtained for the entire range of Cu content show good agreement with available experimental data. The magnetic order for x<xc has only a subtle influence on the phonon modes, but induces important changes in the dynamical coupling of first- and second-nearest neighbor bonds. While variations in the first-nearest neighbor coupling are linked to structural, chemical and magnetic changes along the alloy series, the second-nearest neighbor is almost entirely sensitive to the magnetic order only.