Magnetism on Au Oxide Surfaces and O-Adsorbed Au and Ag Surfaces, and Work Functions

Abstract

We reveal magnetic ordering in vacancy-containing Au2O3, on Au2O3 surfaces, and on O-adsorbed Au surfaces, using density functional theory and hybrid functional theory. O 2p holes, enriched by reduced Au−O coordination, induce magnetization 0.2−0.8 μB per surface O atom, whereas Au−O coordination tends to favor ferromagnetic (FM) ordering. The balance between these effects depends on surface reconstruction, thereby forming two-dimensional local FM ordering. On extended surfaces, these local FM orderings mostly manifest as antiferromagnetic (AF) nanoarrangements, outlined by chemical-bonding units, and, in a few cases, FM arrangements. These AF arrangements provide a magnetic field region that can be utilized by molecules, e.g., in catalysis. Further, the small free-energy differences between the various AF arrangements offer potential for manipulating these nanoregions in applications. On Au and Ag surfaces, adsorbed O atoms transition from chemisorption to physisorption-like with increasing O-layers, and at 200% O coverage, O atoms resemble O2 molecules and exhibit typical AF ordering. We also report the magnetic properties of O-covered Ag surfaces and resolve existing discrepancies between theory and experiments on magnetism. Additionally, work functions of different facets of Au2O3 and Au2O are also reported.