Magnetism of linear chains

Accurate self-consistent local spin density electronic structure calculations for linear chains of Ni and Fe atoms are presented which realistically treat three-dimensional nature. The one-dimensional character of the bands manifests itself in high density of states arising from van Hove singularities. Both transition metals are "strong" Stoner ferromagnets with large magnetic moments (3.3 and 1.1μ_B for Fe and Ni, respectively) and have large s- and d-exchange splittings. From fits of our results to simple tight-binding models, we find that the d-d effective exchange interaction is similar to that in bulk. However, the use of standard bulk tight-binding parameters is found to be inappropriate since they qualitatively change the results by, for example, misplacing the Fermi level with respect to the band edges. Moreover, in contrast to the bulk, the linear chains also show a rather large s-exchange interaction and hence a large and positive valence contribution to the contract hyperfine field; for Fe this results in a positive contact hyperfine field of the same magnitude as in the bulk. The unique signatures of these linear systems should make their characterization experimentally feasible.