Energetics of Co adatoms on the Cu(001) surface

Abstract

By using an N-body potential scheme constructed by fitting the interaction parameters to accurate firstprinciples calculations, we investigate the structural stability of Co atoms and clusters deposited on Cu͑100͒. We found that Co atoms and clusters prefer to be embedded inside the substrate, in a way compatible with the formation of a surface alloy observed experimentally. Enhanced stability is achieved when Co atoms are deposited on a preformed Co cluster embedded on the uppermost layer of the substrate. Co atoms deposited on Co islands are best stabilized when they concur to complete the islands, by promoting layer-by-layer growth.Ultrathin films of ferromagnetic metals have found considerable interest in recent years due to their technological applications in the area of magneto-optical and transport properties. [1][2][3] In particular the growth of Fe and Co films on Cu͑001͒, which takes place pseudomorphically on the fcc substrate, has been investigated extensively.4-10 The quality of the grown layers and of the interfaces has a strong influence on properties like giant magnetoresistance, 5 magnetic anisotropy, 6,7 and oscillatory interlayer exchange coupling. 8,9Kief and Egelhoff 10 have reported the observation of nonideal film growth, characterized by the formation of compact Co clusters and the segregation of substituted Cu on the surface. Recently, the interfacial intermixing of ultrathin Co films on a Cu͑001͒ was observed, 11 despite the fact that Co and Cu are immiscible in the bulk. 12 The intermixing in the upper layers might not only be favored kinetically, but also energetically. 13In this paper we resort to a newly developed n-body interatomic potential scheme to ascertain the energetics of atoms and clusters of Co on the Cu͑001͒. A strong tendency for a direct exchange mechanism into the Cu layer is found. Our results demonstrate that at the initial stage of monolayer growth small Co clusters are formed in the Cu surface. We investigate the mechanism of adatom-cluster interactions and show how heteroepitaxial thin film growth takes place.Our approach is based on accurate first-principles calculations of selected cluster-substrate properties, which have been employed in the fitting of the potential parameters. This results in a manageable and inexpensive scheme able to account for structural relaxation and including implicitly magnetic effects, crucial for a realistic determination of interatomic interactions in systems having a magnetic nature.The potentials are formulated in the second moment tightbinding approximation ͑TB-SMA͒.14,15 The attractive term ͑band energy͒ E B i contains the many-body interaction. The repulsive term E R i is described by pair interactions ͑Born-Mayer form͒. The cohesive energy E coh is the sum of the band energy and repulsive part:. ͑3͒ r i j is the distance between the atoms i and j. r 0 ␣␤ is the first neighbor distance in the crystalline structures of the pure metals for atom-like interactions and becomes an adjustable parameter in the case of the cross interac...

Magnetic anisotropy of vicinal (001) fcc Co films: Role of crystal splitting and structure relaxation in the step-decoration effect

“…(5) It includes the band energy E B and the pair potentials V P which are given by the analytical formulae with parameters fitted 39 to reproduce various elastic properties either known from experiment for Cu or found with firstprinciple methods for Co and Co/Cu systems. This semi-empirical model, based on the second moment tightbinding approximation, was previously used to find strain relief and shape evolution for a Co island on Cu surface.…”

Co diffusion in the near-surface region of Cu

“…A detail theoretical work by Levanov et al shows that the locations of a single Co atom in the first two atomic layers of Cu(001) provide higher energies than the locations in the deeper layers [45]. In that work, they show that the difference of energy due to the embedding in the first and second layer is larger than it is due to the embedding in the second and deeper layers.…”

“…The energetics of the Co-Cu(001) system favors Co to be located below the first layer rather than on the surface or in the first layer [45,46]. A detail theoretical work by Levanov et al shows that the locations of a single Co atom in the first two atomic layers of Cu(001) provide higher energies than the locations in the deeper layers [45].…”

Genetic programming for multitimescale modeling

“…We model the atomic interactions with a simple Morse potential [17] and a tight-binding potential with secondmoment approximation (TB-SMA) [18]. To validate interactions, we model vacancy-assisted migration on (100)-surface of Cu and consider only first n.n.…”