Reversible enhancement of the magnetism of ultrathin Co films by H adsorption

TL;DR

This study uses ab initio calculations to explore how hydrogen adsorption affects the structural, electronic, and magnetic properties of ultrathin cobalt films on Ru(0001), revealing conditions that enhance surface magnetism.

Contribution

It demonstrates that partial hydrogen coverage can selectively increase the magnetic moments of surface Co atoms, a novel insight into tuning magnetic properties via H adsorption.

Findings

Hydrogen prefers hollow sites, maintaining 3-fold symmetry.

Complete H overlayers stabilize the surface with strong H-Co bonds.

Partial H coverage enhances magnetism of non-bonded surface Co atoms.

Abstract

By means of ab initio calculations, we have investigated the effect of H adsorption in the structural, electronic and magnetic properties of ultrathin Co films on Ru(0001). Our calculations predict that H occupies hollow sites preserving the two-dimensional 3-fold symmetry. The formation of a complete H overlayer leads to a very stable surface with strong H-Co bonds. H tends to suppress surface features, in particular, the enhancement of the magnetic moments of the bare film. The H-induced effects are mostly confined to the Co atoms bonded to H, independent of the H coverage or of the thickness and the structure of the Co film. However, for partial H coverages a significant increase occurs in the magnetic moment for the surface Co atoms not bonded to H, leading to a net enhancement of surface magnetism.