Giant magnetic moments and magnetic bistability of stoichiometric MnO clusters

Ab initio calculations based on density functional theory and generalized gradient approximation reveal many unusual features of stoichiometric (MnO)(x) (x less than or equal to 9) clusters that contrast with their bulk behavior. The clusters are ferromagnetic and carry atomiclike magnetic moments ranging from 4 mu(B) to 5 mu(B) per MnO unit, and the moments are localized at the Mn sites. The (MnO)(8) cluster, in particular, exhibits nearly degenerate ferromagnetic and atypical antiferromagnetic solutions with the ferromagnetic structure carrying a moment of 40 mu(B). The structures of (MnO)(lambda) clusters are also unique with cubic and hexagonal forms competing for stability. (MnO)(2) and (MnO)(3) are unusually stable and form the foundation for further growth.