Giant Magnetic Moments and Magnetic Bistability of Stoichiomatric MnO Clusters

{ital Abthinspthinspinitio} calculations based on density functional theory and generalized gradient approximation reveal many unusual features of stoichiometric (MnO){sub x} (x{le}9) clusters that contrast with their bulk behavior. The clusters are ferromagnetic and carry atomiclike magnetic moments ranging from 4{mu}{sub B} to 5{mu}{sub B} per MnO unit, and the moments are localized at the Mn sites. The (MnO){sub 8} cluster, in particular, exhibits nearly degenerate ferromagnetic and atypical antiferromagnetic solutions with the ferromagnetic structure carrying a moment of 40{mu}{sub B} . The structures of (MnO){sub x} clusters are also unique with cubic and hexagonal forms competing for stability. (MnO){sub 2} and (MnO){sub 3} are unusually stable and form the foundation for further growth. {copyright} {ital 1998} {ital The American Physical Society}