Electronic and magnetic structure of idealized metallic multilayers:Ni3Fe-FeMn system

We have studied the magnetic structure of three different superlattices composed of alternating layers of ${\mathrm{Ni}}_3$Fe and FeMn, arranged in real as well as hypothetical ordered phases. Since the constituent compounds have the fcc structure and nearly the same lattice constant, we consider alternating lattice-matched slabs as idealizations of multilayered systems. By carrying out spin-polarized self-consistent linear muffin-tin orbital band-structure calculations, we have determined the magnetic and electronic properties of superlattices composed of Fe, Ni, and Mn atoms located on a common fcc sublattice. For reasons of computational economy, we limited ourselves to heterostructures modulated along the [001] direction and to very thin slabs. For each of the structures studied, the superlattice unit cell contains eight atoms, with two atoms each on four successive atomic planes. The essential results are as follows: First, the individual atomic moments are not very different from their corresponding values in bulk ${\mathrm{Ni}}_3$Fe and FeMn compounds. Second, the spins in the atomic planes parallel to the interfaces are ferromagnetically coupled to one other, with, for instance "up" spins for the ${\mathrm{Ni}}_3$Fe planes and alternating "up" and "down" spins for the FeMn planes. In view of these results, we can expect exchange anisotropy to occur in such multilayers. This theoretical conclusion is consistent with experimental observations of unidirectional anisotropy in two-phase systems composed of Permalloy and FeMn alloys.