s-Electron Ferromagnetism in Gold and Silver Nanoclusters

Ferromagnetic (FM) ordering in transition-metal systems (solids, surface layers, nanoparticles) arises from partially filled d shells. Thus, recent observations of FM Au nanoclusters was unexpected, and an explanation has remained elusive. Here we report first-principles density-functional spin-polarized calculations for Au and Ag nanoclusters. We find that the highest-occupied level is highly degenerate and partially filled by s electrons with spins aligned according to Hund's rule. The nanoclusters behave like "superatoms", with the spin-aligned electrons being itinerant on the outer shell of atoms.