Orbital magnetism of transition-metal adatoms and clusters on the Ag and Au(001) surfaces

Abstract

We present ab initio calculations of the orbital moments and magnetocrystalline anisotropy energies for 3d, 4d, and 5d transition-metal adatoms and for some selected small clusters on the ͑001͒ surfaces of Ag and Au. The calculations are based on the local density approximation of density functional theory and apply a fully relativistic Koringa-Kohn-Rostoker Green's function method. Due to the reduced coordination of the adatoms and the weak hybridization with the substrate, we find fairly large orbital moments, in particular for the elements towards the end of the series. The general trend can be understood from a simple tight-binding model. The orbital moments are connected with very large anisotropy energies. While the orbital moments are on the Ag substrate somewhat larger than on Au, the magnetic anisotropy has about the same size for both substrates. Calculations for small clusters of Fe, Ru, and Os adatoms show, that due to interaction effects the orbital moments are strongly reduced, e.g., by 50% for the dimer atoms. The size of the reduction correlates well with the coordination number. Similar reductions also occur for the magnetic anisotropy energies.

Evolution of magnetism of Cr nanoclusters on Au(111): First-principles electronic structure calculations

“…1 Magnetic transition-metal nanostructures on nonmagnetic substrates have attracted recently large attention due to their unusual magnetic properties. 2,3 The supported clusters experience both the reduction of the local coordination number, as in free clusters, as well as the interactions with the electronic degrees of freedom of the substrate, as in embedded clusters, which may lead to the Kondo effect. 4 The complex magnetic behavior is usually associated with the competition of several interactions, such as interatomic exchange and bonding interactions, the Kondo effect, and in some cases noncollinear effects, which can give rise to several metastable states close in energy.…”

Extremely long-lived magnetic excitations in supported Fe chains

“…The very long lifetimes in the system are very sensitive to small variations in the magnetic structure parameters (exchange coupling and anisotropies). Computation of magnetic structure parameters have been performed via configuration interaction or DFT approaches for a variety of nanostructures at surfaces systems 15,18,19,20,43,44,45,46,47 . Further studies by ab initio approaches on the present system could be highly conclusive, despite the current difficulties in accurately computing magnetic structure parameters 48,49 .…”

Ensemble magnetic behavior of interacting CoFe nanoparticles

“…Several studies in recent years have considered the enhanced orbital moment predicted [12,13] and observed [14,15] in sub 12 nm diameter single domain particles. The enhancement of the orbital moment is highly size dependent and clearly marks the territory between magnetic atoms obeying Hund's rules, and bulk-like ferromagnetism with highly quenched orbital magnetism.…”