GIANT MAGNETIC-MOMENTS AND MAGNETIC BISTABILITY OF STOICHIOMETRIC MNOCLUSTERS

Ab initio calculations based on density functional theory and generali zed gradient approximation reveal many unusual features of stoichiomet ric (MnO)(x) (x less than or equal to 9) clusters that contrast with t heir bulk behavior. The clusters are ferromagnetic and carry atomiclik e magnetic moments ranging from 4 mu(B) to 5 mu(B) per MnO unit, and t he moments are localized at the Mn sites. The (MnO)(8) cluster, in par ticular, exhibits nearly degenerate ferromagnetic and atypical antifer romagnetic solutions with the ferromagnetic structure carrying a momen t of 40 mu(B). The structures of (MnO)(lambda) clusters are also uniqu e with cubic and hexagonal forms competing for stability. (MnO)(2) and (MnO)(3) are unusually stable and form the foundation for further gro wth.