Unusual Structure and Magnetism in MnO Nanoclusters*

We report an unusual structural and magnetic evolution in stoichiometric MnO nanoclusters by an extensive and unbiased search through the potential energy surface within density functional theory. The $(MnO)_n$ nanoclusters adopt two-dimensional structures in size ranges in which $Mn_n$ nanoclusters are three-dimensional and regardless of the size of the nanocluster, the magnetic coupling is found to be antiferromagnetic, and is strikingly different from Mn-based molecular magnets. Both of these features are explained through the inherent electronic structures of the nanoclusters.