Elastic and chemical contributions to the stability of magnetic surface alloys on Ru(0001)

Abstract

We have used density functional theory to study the structural stability of surface alloys. Our systems consist of a single pseudomorphic layer of MxN1−x on the Ru(0001) surface, where M = Fe or Co, and N = Pt, Au, Ag, Cd, or Pb. Several of the combinations studied by us display a preference for atomically mixed configurations over phase-segregated forms. We have also performed further ab initio calculations to obtain the parameters describing the elastic interactions between atoms in the alloy layer, including the effective atomic sizes at the surface. We find that while elastic interactions favor alloying for all the systems considered by us, in some cases chemical interactions disfavor atomic mixing. We show that a simple criterion (analogous to the Hume-Rothery first law for bulk alloys) need not necessarily work for strain-stabilized surface alloys, because of the presence of additional elastic contributions to the alloy heat of formation, that will tend to oppose phase segregation.

Magnetism of surface alloys of the type MxN1−x/Rh(111)

“…2) that some of these pairs (Co-Ag, Fe-Ag) do not quite mix on Rh(1 1 1) too. Our finding for Co-Ag is similar to the experimental finding by Thayer et al on Ru(0 0 0 1) [25] as well as corresponding first-principles calculations [24,25]. In the experiment they found that Ag and Co on Ru(0 0 0 1) do not show atomic-level mixing.…”

“…In earlier work, we have already reported on the mixing and some magnetic properties of two-dimensional magnetic surface alloys of the form M x N 1 À x on Ru(0 0 0 1) [24]. In this paper, we present results on the magnetic properties of similar surface alloys on a Rh(1 1 1) substrate.…”

“…So we separate out the contribution of elastic and chemical effects to DH. In order to do this, we follow a procedure similar to that carried out for the surface alloys on Ru(0 0 0 1) [24].…”

Mixing and magnetic properties of surface alloys: The role of the substrate

“…We have already reported a study of the mixing and magnetic properties of (i) systems of the type M x N 1Àx /S, where M is a magnetic element (Fe or Co), N is a non-magnetic element (Pt, Au, Ag, Cd or Pb), and S is Ru(0 0 0 1) [10], and (ii) Co-Ag on Rh(1 1 1) [11] and (iii) Ni-Pt on Rh(1 1 1) [12]. These studies were performed using ab initio density functional theory calculations.…”

Structural Order-Disorder Transitions and Phonon Conductivity of Partially Filled Skutterudites

“…We use the Morse and three-cosine potentials, parameterized for two-body (Co-Sb, Co-Co, Sb-Sb, and Ba-Sb) and three-body (Co-Sb-Sb) interactions [20,22,28]. Interatomic potentials are simplified fields and the CRs are approximations, therefore these potentials cannot accurately predict, for example, formation energy.…”